Context: Table II. Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity. For loam, very fine sandy loam, or silt loam topsoil which is silty clay loam or silty clay subsoil, the available water in 1 foot of soil at 100% of available water is 2.0 in/ft, the available water in top 4 feet at 100% of available water is 8.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 3.2 in/ft. For loam, very fine sandy loam, or silt loam topsoil which is medium textured subsoil, the available water in 1 foot of soil at 100% of available water is 2.5 in/ft, the available water in top 4 feet at 100% of available water is 10.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 4.0 in/ft.

Question: what is the available water in 1ft of soil at 100% of available water for loam, very fine sandy loam, or silt loam topsoil which is silty clay loam or silty clay subsoil?

Answer: 2.0 in/ft,

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: For dry edible beans in the emergence-10% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.07 inches and the estimated water use during the week of June 19-25, 2023 is 0.50 inches. For dry edible beans in the 10-50% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.07 inches.

Question: what was the estimated water usage for dry edible beans during emergence ~10% cover crop growth stage during the week of June 12-18 in 2023?

Answer: 0.07 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: Keep in mind that the plants next to the probes are an integral part of the sensor and must be protected so they can represent all the other plants in the field. Do not install sensors when the soil is too wet and make as few footprints as possible to prevent soil compaction.

Question: when should sensors not be installed?

Answer: when the soil is too wet

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Different methods can be used to determine how many gallons/hour (gph) the chemigation injection pump should be set to inject. We are going to talk about two of them today. The first one is using the 'speed chart' (water application depth per pass chart) in the 'sprinkler chart' for the pivot or looking up circle time on the computer panel or the pivot app. The second one involves calculating the chemical injection rate using a spreadsheet. This method gives you more details about the system and is still easy to figure. You will just need to enter the basic information for the pivot. If you are interested, download the spreadsheet from UNL Water.

Question: where can an irrigator find a useable spreadsheet that will help determine the chemigation injection pump setting?

Answer: UNL Water

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Percent of fields that became wetter moving from August to Sept. 15. The dry years 2020, '21 and '22 fields are much drier than the other years in the fall.  In 2019, 54% of fields with soil in the 15-25 in zone became wetter from August to Sept. 15, 54% of fields with soil in the 25-36 in zone became wetter from August to Sept. 15, and 38% of fields with soil in both zones became wetter moving from August to Sept. 15.

Question: what percentage of fields with soil in the 25-36 inch zone became wetter from August to Sept. 15 in 2019?

Answer: 54%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Carefully Consider Decisions to Apply Water in May and June. Decisions to irrigate in May and June need to be considered very carefully. Long-term averages show May and June to be two of the highest rainfall months in Nebraska. The rainfall is usually more than needed to refill the soil profile for fields that were irrigated the previous year.

Question: why should the decision to irrigate a field in Nebraska in May and June be carefully considered?

Answer: Long-term averages show May and June to be two of the highest rainfall months in Nebraska

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Percent of fields that became wetter moving from August to Sept. 15. The dry years 2020, '21 and '22 fields are much drier than the other years in the fall.  In 2018, 58% of fields with soil in the 15-25 in zone became wetter from August to Sept. 15, 58% of fields with soil in the 25-36 in zone became wetter from August to Sept. 15, and 47% of fields with soil in both zones became wetter moving from August to Sept. 15.

Question: what percentage of fields with soil in the 15-25 inch zone and 25-36 inch zone became wetter from August to Sept. 15 in 2018?

Answer: 47%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Support for People Wanting to Improve Their Irrigation Management For those who have not collected data in the past or would like to hone their scheduling skills, take some time now to figure out what will work best for your operation. Many resources are available to help. A great five-part video series on this topic can be found on the CropWatch YouTube channel at: How to Schedule Irrigations with Soil Water Data.

Question: where can a grower find a great five-part video series on the topic of crop irrigation management?

Answer: CropWatch YouTube channel

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: For pasture grass in the actively growing crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.00 inches and the estimated water use during the week of June 19-25, 2023 is 1.50 inches.

Question: what is the estimated water usage for pasture grasses during the actively growing crop growth stage during the week of June 12-18 in 2023?

Answer: 1.00 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: Both methods require the basic information for the pivot. All the needed details can be found on the sprinkler chart for the center pivot. The sprinkler chart is the documentation that came with the sprinkler package for the pivot and describes the basic layout of the pivot, water flow rate, pressure, size of each sprinkler, etc. If the current sprinklers on the pivot came with the machine when it was new, the pivot dealer should be able to provide a copy. Otherwise, ask the company that sold the current sprinkler package for it. If you do not have the sprinkler chart, then you will need to determine the needed data by measuring the pivot.

Question: who can provide a copy of the sprinkler chart if the current sprinklers on the pivot came with the machine when it was new and the pivot dealer can't provide a copy?

Answer: the company that sold the current sprinkler package for it

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: For alfalfa in the stage 4 crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.22 inches and the estimated water use during the week of June 19-25, 2023 is 2.05 inches. For alfalfa in the maturity crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.30 inches. For alfalfa in the full cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.18 inches.

Question: what is the estimated water usage for alfalfa during the full cover crop growth stage during the week of June 12-18 in 2023?

Answer: 1.18 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: Differences in Late-Season Irrigation Timing for Corn/Sorghum and Beans: Corn/sorghum and beans are somewhat different in respect to crop water use as they approach maturity. For example, if hot dry windy conditions are experienced in September, daily crop water use will increase. However, since corn/sorghum develop based on heat units, they will use more water per day, but will mature in fewer days using about the average amount of water shown in the chart.

Question: what are two crops that develop based on heat units?

Answer: corn/sorghum

Melvin, S. (2017). Predicting Late-Season Irrigation Needs. UNL Water. https://water.unl.edu/article/agricultural-irrigation/predicting-late-season-irrigation-needs


Context: To learn more about the secondary aquifers of Nebraska, download the Conservation and Survey Division publication titled 'An Overview of Secondary Aquifers in Nebraska' available at http://digitalcommons.unl.edu/conservationsurvey/138. Questions regarding western Nebraska aquifers may be directed to xxxxx xxxxxx atxxxxxxxxxxxxx; questions regarding eastern Nebraska aquifers may be directed to xxxx xxxxxx atxxxxxxxxxxxxx.

Question: how can xxxx xxxxxx be contacted?

Answer: xxxxxxxxxxxx

Divine, D. (2017). An Overview of Secondary Aquifers in Nebraska | UNL Water. https://water.unl.edu/article/agricultural-irrigation/overview-seondary-aquifers-nebraska


Context: Getting the crop off to a great start is essential for a successful season. On dry years, it is sometimes necessary to start irrigating in May and June. However, it is critical to monitor soil moisture to balance crop needs with the risk of losing nitrogen and other valuable crop inputs. Monitoring will also help prevent unnecessary irrigation expenses, and if you have a water allocation, avoid using up water that is critical for later growth stages.

Question: if a grower has water allocation what should they avoid doing?

Answer: using up water that is critical for later growth stages

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: The description of a static VRI irrigation prescription is that this prescription stays the same or changes only a few times during the season. Considerations include that it is relatively simple to apply. Does not account for change in spatial variability over a season. Example uses include avoiding irrigation on uncrossed areas, mining differences in soil available water capacity, and variable rate chemigation.

Question: what is a description for a static VRI irrigation prescription?

Answer: prescription stays the same or changes only a few times during the season

Barker, J. B. (2017). Considerations in Adopting Variable Rate Irrigation for Center Pivots and Lateral Systems. http://extensionpublications.unl.edu/assets/pdf/ec2000.pdf.


Context: Percent of fields that became wetter moving from August to Sept. 15. The dry years 2020, '21 and '22 fields are much drier than the other years in the fall.  In 2021, 44% of fields with soil in the 15-25 in zone became wetter from August to Sept. 15, 48% of fields with soil in the 25-36 in zone became wetter from August to Sept. 15, and 37% of fields with soil in both zones became wetter moving from August to Sept. 15.

Question: what percentage of fields with soil in the 15-25 inch zone and 25-36 zone became wetter from August to Sept. 15 in 2021?

Answer: 37%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Table II. Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity. For fine sands, the available water in 1 foot of soil at 100% of available water is 1.0 in/ft, the available water in top 4 feet at 100% of available water is 4.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 1.6 in/ft. For loamy sands, the available water in 1 foot of soil at 100% of available water is 1.1 in/ft, the available water in top 4 feet at 100% of available water is 4.4 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 1.8 in/ft. For sandy loams, the available water in 1 foot of soil at 100% of available water is 1.4 in/ft, the available water in top 4 feet at 100% of available water is 5.6 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.2 in/ft.

Question: what is the amount of available water in units of (in/ft) for fine sands at 100% of available water in 1 ft of soil?

Answer: 1.0 in/ft

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2019, out of 15 reports, 20% were ranked good, 7% were fair, 40% were wet late, 7% were wet early, 0% were wet all season, and 27% were very wet all season.

Question: In 2019 out of 15 reports, what percentage of Nebraska fields were ranked fair?

Answer: 7%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: For soybeans in the V1 1st Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.24 inches and the estimated water use during the week of June 19-25, 2023 is 1.30 inches. For soybeans in the V2 2nd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.47 inches. For soybeans in the V3 3rd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.71 inches.

Question: what was the estimated water usage for soybeans during the V2 second node crop growth stage during the week of June 12-18 in 2023?

Answer: 0.47 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: To determine the actual cost, we would recommend the use of the IrrigateCost app. The app, which is available for both Apple and Android products, allows users to input their specific information such as acres irrigated, pumping lift, system PSI, pump and pivot life, and inches applied as well as related costs such as for the well and engine, labor, energy, district fees, and taxes. The app then calculates total irrigation cost as well as total ownership and total operating costs.  It also breaks down costs by irrigation well, pump, gear head, pump base, diesel engine and tank and system and calculates per acre annual cost and per acre-inch annual cost.

Question: what related costs does the IrrigateCost app allow user to input in?

Answer: the well and engine, labor, energy, district fees, and taxes

Nygren, A. (2017). Value of Using Sensors to Manage Irrigation and Tips for Proper Installation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/value-using-sensors-manage-irrigation-and-tips-proper-installation


Context: When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.02, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.96. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.03, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.94. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.04, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.92. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.05, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.91. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.06, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.89. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.07, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.87. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.08, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.86. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.09, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.84. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.1, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.83. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.11, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.81. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.12, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.8. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.13, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.78. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.14, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.77. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.15, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.76. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.16, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.74. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.17, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.73. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.18, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.72. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.19, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.71. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.2, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.69.

Question: what is the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) when the ratio of the end gun throw (Rg) to the pivot length (R) is 0.02?

Answer: 96

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: The analysis focused on dividing the fields into one of six categories based on the soil water levels in the heart of the season (July and August) and on Sept. 15. The six categories were developed based on the readings from the Watermark sensors. The sensors generate data reported in centibars and have a range from 0 (wet) to 240 (dryer) centibars (cb). Centibar is a unit of measure that refers to the force required by the plant to pull the water out of the soil and into the plant. Typically, installations use a set of three sensors, with one sensor installed at six to 12 inches, one at 18-24 inches, and one at 30-36 inches.

Question: what does the centibar unit represent?

Answer: force required by the plant to pull the water out of the soil and into the plant

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2017, out of 86 reports, 28% were ranked good, 10% were fair, 13% were wet late, 13% were wet early, 22% were wet all season, and 14% were very wet all season.

Question: In 2017 out of 86 reports, what percentage of Nebraska fields were considered very wet all season?

Answer: 14%

Heeren, D., Barker, J. B., Lo, T. H., Melvin, S., Martin, D., & Luck, J. (2017). Considerations in Adopting Variable Rate Irrigation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/considerations-adopting-variable-rate-irrigation


Context: Once the system is up to pressure it is a good idea to check the system for leaks and operation of the sprinklers.  If you find missing or inoperable sprinklers refer to the sprinkler chart that was developed for the system to find the correct replacement.  If the system is on rolling or hilly terrain, regulators are also needed for uniform application and definitely should be checked.

Question: If you find any missing inoperable sprinkler what should an irrigator check to find the correct replacements?

Answer: the sprinkler chart that was developed for the system

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Context: Using this information for a center pivot that is set to apply one inch of water per irrigation, the suggested recommendation would be that the system should be off for the next few days to use some of the remaining water. The next inch of water should be applied within the next seven days. Then, the next irrigation should be recalculated using updated soil water readings. The best way to use the remaining water is to delay the start of the last few irrigations a few days each time and react to any rain that might occur during the period. Slowly using the water in the lower portion of the root zone starting in early to mid-August is much better than keeping the profile full until the very end and expecting the crop to use the water all at once.

Question: what is slowly using the water in the lower portion of the root zone starting early to mid-August much better than?

Answer: keeping the profile full until the very end and expecting the crop to use the water all at once.

Melvin, S. (2017). Predicting Late-Season Irrigation Needs. UNL Water. https://water.unl.edu/article/agricultural-irrigation/predicting-late-season-irrigation-needs


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In the weighted average dry years, 2020, 2021, 2022, 64% were ranked good, 11% were fair, 3% were wet late, 15% were wet early, 3% were wet all season, and 4% were very wet all season.

Question: what percentage of Nebraska fields were wet late in the dry years of 2020, 2021, and 2022?

Answer: 3%

Heeren, D., Barker, J. B., Lo, T. H., Melvin, S., Martin, D., & Luck, J. (2017). Considerations in Adopting Variable Rate Irrigation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/considerations-adopting-variable-rate-irrigation


Context: Table II. Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity. For silt clay or clay, the available water in 1 foot of soil at 100% of available water is 1.6 in/ft, the available water in top 4 feet at 100% of available water is 6.4 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.6 in/ft. For fine sandy loam, silty clay loam, or clay loam, the available water in 1 foot of soil at 100% of available water is 1.8 in/ft, the available water in top 4 feet at 100% of available water is 7.2 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.9 in/ft. For sandy clay loam, the available water in 1 foot of soil at 100% of available water is 2.0 in/ft, the available water in top 4 feet at 100% of available water is 8.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 3.2 in/ft.

Question: what is the minimum balance for water in the top 4ft of fine sandy loam, silty clay loam, or clay loam soils at 40% of available water?

Answer: 2.9 in/ft

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Soil water monitoring data is easier to analyze once the crop has taken up water at the 16- to 24-inch depth during the vegetative growth stage. This drier zone can then be monitored with sensors to see if the area gets wetter or drier. If it keeps getting drier, the irrigation system needs to keep running. However, if it starts to get wetter, then stop irrigating for a few days. Ideally, the drier zone should slowly expand deeper with the crop using most of the subsoil water by the time the crop matures. For more information on this scheduling strategy, watch the Advanced Irrigation Scheduling Techniques video.

Question: ideally what should the drier zone do as the crop matures?

Answer: slowly expand deeper with the crop using most of the subsoil water by the time the crop matures

Yonts, C. D., Lyon, D. J., Harveson, R. M., Hergert, G. W., Hein, G. L., & Santra, D. (2009). Producing Irrigated Winter Wheat. https://extensionpubs.unl.edu/publication/ec731/pdf/view/ec731-2009.pdf


Context: The top foot will go above field capacity (30cb) after every irrigation or heavy rain. However, if the second foot gets above 30 cb, it would indicate that over-irrigation is occurring. The data in the chart indicated that the field was this dry on a given day and not how many days the soil was drier than 70 cb. The 70 cb level is equal to about 70% of plant available water (PAW) and stress should not start until below 50% of PAW during the summer and 40% in late August and September. Soil types such as those with high sand or clay content would require different levels other than 30 and 70 cb.

Question: what is PAW short for?

Answer: plant available water

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Also, keep in mind the corn roots grow about an inch each day into soil that is at field capacity, providing much of the water the plants need for that day. Generally, irrigation needs to be delayed until the soil begins to dry down. Furthermore, research conducted in the North Platte area has shown that irrigation could be reduced by one to four inches, compared to a fully irrigated crop, during the vegetative period without a significant yield reduction and can stimulate deeper root growth. For more information, go to "Vegetative Growth Stage Irrigation, Is It Needed This Year?"

Question: generally, when does irrigation need to be delayed?

Answer: until the soil begins to dry down

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: Many irrigators apply more water than necessary toward the end of the irrigation season because the crop is using less water per day. The crop is getting more mature and the days are getting shorter and cooler. The average crop water use rate drops from around 2.1 inches per week at silking to only about 1.2 inches per week by the full dent stage. This 40% reduction requires irrigators to adjust their thinking about how much water needs to be applied each week.

Question: what are contributing factors to a crop using less water per day late in the season?

Answer: The crop is getting more mature and the days are getting shorter and cooler

Melvin, S. (2017). Predicting Late-Season Irrigation Needs. UNL Water. https://water.unl.edu/article/agricultural-irrigation/predicting-late-season-irrigation-needs


Context: The Nebraska Extension NebGuide G888, Flow Control Devices for Center Pivot Irrigation Systems, describes the working principles of pressure regulators and provides guidelines for selecting a regulator. When regulators stop functioning properly, due to a worn out diaphragm and/or spring, they no longer provide the desired constant outlet pressure, and consequently flow rate.

Question: where can you find descriptions of the working principles of pressure regulators and provides guidelines for selecting a regulator?

Answer: The Nebraska Extension NebGuide G888, Flow Control Devices for Center Pivot Irrigation Systems

Rudnick, D. (2016). Sprinkler Irrigation System Maintenance for Improved Uniformity and Application Efficiency | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2016/sprinkler-irrigation-system-maintenance-improved-uniformity-and-application-efficiency


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2018, out of 50 reports, 40% were ranked good, 18% were fair, 16% were wet late, 12% were wet early, 10% were wet all season, and 4% were very wet all season.

Question: In 2018 out of 50 reports, what percentage of Nebraska fields were ranked good?

Answer: 40%

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Question: what is the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) when the ratio of the end gun throw (Rg) to the pivot length (R) is 0.06?

Answer: 0.89

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: The categories are as follows: Good - At least one sensor out of the three depths drier than 70 cb early and one sensor drier than 70 cb on 9/15. Fair - At least one sensor drier than 70 cb early and one sensor drier than 30 cb on 9/15. Wet Late - At least one sensor drier than 70 cb early but no sensor drier than 30 cb on 9/15. Wet Early - No sensor drier than 70 cb early, but one sensor drier than 30 cb on 9/15. Wet All Season - Both sensors measuring the second and third foot not drier than 70 cb all year, but one sensor between 30 to 70 cb on Sept. 15. Very Wet All Season - Both sensors measuring second and third foot not drier than 70 cb all year and no sensor drier than 30 cb on Sept. 15.

Question: what is the criteria for a field to be considered "wet all season"?

Answer: Both sensors measuring the second and third foot not drier than 70 cb all year, but one sensor between 30 to 70 cb on Sept. 15

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Both methods require the basic information for the pivot. All the needed details can be found on the sprinkler chart for the center pivot. The sprinkler chart is the documentation that came with the sprinkler package for the pivot and describes the basic layout of the pivot, water flow rate, pressure, size of each sprinkler, etc. If the current sprinklers on the pivot came with the machine when it was new, the pivot dealer should be able to provide a copy. Otherwise, ask the company that sold the current sprinkler package for it. If you do not have the sprinkler chart, then you will need to determine the needed data by measuring the pivot.

Question: if you don't have a sprinkler chart how can you determine the necessary data for estimating the chemigation irrigation pump setting?

Answer: by measuring the pivot

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Question: during what stage of crop growth does the research in the North Platte area indicate irrigation can be reduced without a significant yield reduction and stimulate deeper root growth?

Answer: vegetative period

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2020, out of 39 reports, 64% were ranked good, 21% were fair, 0% were wet late, 3% were wet early, 5% were wet all season, and 8% were very wet all season.

Question: In 2020 out of 39 reports, what percentage of Nebraska fields were ranked good?

Answer: 64%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Carefully Consider Decisions to Apply Water in May and June. Decisions to irrigate in May and June need to be considered very carefully. Long-term averages show May and June to be two of the highest rainfall months in Nebraska. The rainfall is usually more than needed to refill the soil profile for fields that were irrigated the previous year.

Question: what does the rainfall in May and June do for the fields?

Answer: refill the soil profile for fields that were irrigated the previous year

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: The key to early water management is to apply irrigation only when it is needed to get the crop off to a good start, while keeping in mind over-irrigation enables crop input losses. Precision water and nitrogen management can help guide your early season irrigation decisions.

Question: what is the key to early water management while keeping in mind over-irrigation enables crop input losses?

Answer: to apply irrigation only when it is needed to get the crop off to a good start

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: Leave Room for Storing Rainfall Monitoring soil moisture and leaving it moderately dry during the vegetative growth states also leaves room for the soil to store any rainfall that may come. Too wet and you'll lose that rainfall as runoff or deep percolation. Each inch of rainfall you store saves irrigation, input costs and prevents nitrate leaching.

Question: what can leave room for the soil to any rainfall that may come in the future?

Answer: Monitoring soil moisture and leaving it moderately dry during the vegetative growth states

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: June 19,2023  The estimated crop water use for Nebraska Panhandle crops for the previous week and the upcoming week is shown in this table. It is based on data gathered and calculations made by xxxx xxxxx, Nebraska Extension educator, and Dr. xxx xxxx, extension irrigation and water management specialist, both based at the UNL Panhandle Research and Extension Center in Scottsbluff.

Question: where do they work and what two people retrieved data across the Panhandle region in Nebraska to estimate crop water use?

Answer: xxxx xxxxx, Nebraska Extension educator, and Dr. xxx xxxx, extension irrigation and water management specialist, both based at the UNL Panhandle Research and Extension Center in Scottsbluff

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.02, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.96. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.03, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.94. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.04, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.92. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.05, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.91. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.06, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.89. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.07, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.87. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.08, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.86. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.09, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.84. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.1, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.83. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.11, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.81. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.12, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.8. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.13, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.78. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.14, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.77. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.15, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.76. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.16, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.74. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.17, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.73. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.18, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.72. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.19, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.71. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.2, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.69.

Question: what is considered the variable for the pivot speed with the end gun off?

Answer: S

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Soil Sensor Install Tips: If you are installing Watermark sensors, remember to check them before installation to ensure that they are reading properly. When dry, sensors should read 199 kPa. After soaking in water for 10-15 minutes, sensors should read between 0-10 kPa. Values higher than this likely indicate that the sensor needs to be replaced. Before you go to the field to install Watermark sensors, be sure to put the sensors in water and install them wet to eliminate air in the sensor.

Question: what should a Watermark sensor read in kPa when dry?

Answer: 199 kPa

Nygren, A. (2017). Value of Using Sensors to Manage Irrigation and Tips for Proper Installation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/value-using-sensors-manage-irrigation-and-tips-proper-installation


Context: Internal combustion engines need quite a bit more attention.  Change engine oil and all filters.  Check engine hours and refer to the manufactures service interval on valve adjustments and other service that may be needed.  It would also be a good idea to run the Nebraska Extension App IrrigatePump to see where your well stacks up against the Nebraska Pumping Plant Criteria.  This will give you an idea on the efficiency of the power unit and pump.  In the current economic climate we want to be as efficient as possible.

Question: what will checking the using the Nebraska Extension App IrrigatePump give you a better understanding of?

Answer: the efficiency of the power unit and pump

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Question: what is considered the variable name for the end gun throw?

Answer: Rg

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Table II. Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity. For fine sands, the available water in 1 foot of soil at 100% of available water is 1.0 in/ft, the available water in top 4 feet at 100% of available water is 4.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 1.6 in/ft. For loamy sands, the available water in 1 foot of soil at 100% of available water is 1.1 in/ft, the available water in top 4 feet at 100% of available water is 4.4 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 1.8 in/ft. For sandy loams, the available water in 1 foot of soil at 100% of available water is 1.4 in/ft, the available water in top 4 feet at 100% of available water is 5.6 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.2 in/ft.

Question: what is the amount of available water in units of (in/ft) for sandy loam soils at 100% of available water in the top 4ft of soil?

Answer: 5.6 in/4 ft

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Soil water monitoring data is easier to analyze once the crop has taken up water at the 16- to 24-inch depth during the vegetative growth stage. This drier zone can then be monitored with sensors to see if the area gets wetter or drier. If it keeps getting drier, the irrigation system needs to keep running. However, if it starts to get wetter, then stop irrigating for a few days. Ideally, the drier zone should slowly expand deeper with the crop using most of the subsoil water by the time the crop matures. For more information on this scheduling strategy, watch the Advanced Irrigation Scheduling Techniques video.

Question: what is considered the drier zone?

Answer: 16- to 24-inch depth

Yonts, C. D., Lyon, D. J., Harveson, R. M., Hergert, G. W., Hein, G. L., & Santra, D. (2009). Producing Irrigated Winter Wheat. https://extensionpubs.unl.edu/publication/ec731/pdf/view/ec731-2009.pdf


Context: Other secondary aquifers in eastern Nebraska include the Niobrara aquifer (230 wells, mostly in Cedar County), the Codell aquifer (70 wells in Knox and Boyd counties), and the Western Interior Plains Aquifer System. Only one active well is currently installed in the Western Interior Plains Aquifer System in Nebraska, but the aquifer system was a historic source of water to the Omaha area, and still supplies huge volumes of water to Iowa and other states to our east.

Question: What is one aquifer in eastern Nebraska that supplies huge amount of water to Iowa?

Answer: the Western Interior Plains Aquifer System

Divine, D. (2017). An Overview of Secondary Aquifers in Nebraska | UNL Water. https://water.unl.edu/article/agricultural-irrigation/overview-seondary-aquifers-nebraska


Context: Crop water use will vary across the Panhandle due to variations in temperature and precipitation events. Crop water use will assist growers with irrigation scheduling and efficient water use.

Question: what will crop water use data assist growers with?

Answer: irrigation scheduling and efficient water use

Stone, G., & Qiao, X. (2024). Estimated Crop Water Use for May 27-June 2, 2024 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2024/estimated-crop-water-use-may-27-june-2


Context: To illustrate this, let's look at some data from the Upper Big Blue NRD. The NRD requires growers in six areas that have an increased median nitrate-nitrogen level in the groundwater, to use soil water monitoring equipment in one irrigated field and report the data collected annually. Most of the producers impacted by this rule use Watermark sensors that measure soil matric potential; thus, this study has largely focused on Watermark data for easy comparison. The soils in the NRD are mostly a silt loam or similar soil texture, making the field-to-field data comparable as well. The assumption was made that the farmers using Watermark sensors would represent all irrigators in the area. To protect privacy, the NRD removes names from the information prior to group analysis; therefore, the location for each field is an unspecified area in the Upper Big Blue NRD.

Question: how did the NRD protect the privacy of irrigators that provided data in the Upper Big Blue area?

Answer: the NRD removes names from the information prior to group analysis

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Question: what is the minimum balance for water in the top 4ft of sandy loam soils at 40% of available water?

Answer: 2.2 in/ft

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Question: what is the amount of available water in units of (in/ft) for fine sands at 100% of available water in the top 4ft of soil?

Answer: 4.0 in/4 ft

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Table II shows the typical amount of water that will be in the different soils types and can be used to help estimate the volume of water. Remember to use the top 4 ft of soil for the active root zone and plan to use the soil water down to 40% of plant available water (60% depletion) after the dough stage for corn/sorghum and the R5 stage for soybeans/dry beans.

Question: what percentage of plant available water should be used for corn/sorrghum when estimating the volume of water?

Answer: 40%

Melvin, S. (2017). Predicting Late-Season Irrigation Needs. UNL Water. https://water.unl.edu/article/agricultural-irrigation/predicting-late-season-irrigation-needs


Context: The chemigation injection pump setting can be easily determined using the sprinkler chart. The method is very simple to use if one has the chart, or at least the speed chart part of it. The information can also be gained from looking at the readout on a computer-style pivot panel or the pivot control app.

Question: where can the chemigation injection pump setting information be found if a sprinkler chart is not used?

Answer: readout on a computer-style pivot panel or the pivot control app

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Table I. Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska. For Corn R2 crop stage, the stage of growth is known as blister, the approximate days to maturity is 45, and the water use to maturity is 10.5 inches. For Corn R4 crop stage, the stage of growth is known as dough, the approximate days to maturity is 34, and the water use to maturity is 7.5 inches. For Corn R4.7 crop stage, the stage of growth is known as beginning dent, the approximate days to maturity is 24, and the water use to maturity is 5.0 inches. For Corn R5 crop stage, the stage of growth is known as 1/4 milk line, the approximate days to maturity is 19, and the water use to maturity is 3.75 inches. For Corn R5 crop stage, the stage of growth is known as 1/2 milk line - full dent, the approximate days to maturity is 13, and the water use to maturity is 2.25 inches. For Corn R5 crop stage, the stage of growth is known as 13/4 milk line, the approximate days to maturity is 7, and the water use to maturity is 1.0 inches. For Corn R6 crop stage, the stage of growth is known as physiological maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.

Question: what is the approximate water use to maturity for corn in the R4.7 crop stage, the stage of growth that is known as beginning dent?

Answer: 5.0 inches

Yonts, C. D., Melvin, S., & Eisenhauer, D. E. (2008). Predicting the Last Irrigation of the Season. UNL Extension Publications. https://extensionpubs.unl.edu/publication/g1871/html/view


Context: Table I. Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska. For Grain Sorghum stage 6 crop stage, the stage of growth is known as half bloom, the approximate days to maturity is 34, and the water use to maturity is 9.0 inches. For Grain Sorghum stage 7 crop stage, the stage of growth is known as soft dough, the approximate days to maturity is 23, and the water use to maturity is 5.0 inches. For Grain Sorghum stage 8 crop stage, the stage of growth is known as hard dough, the approximate days to maturity is 12, and the water use to maturity is 2.0 inches. For Grain Sorghum stage 9 crop stage, the stage of growth is known as physiological maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.

Question: what is the approximate days to maturity for grain sorghum in the stage 7 crop stage, the stage of growth that is known as soft dough?

Answer: 23

Yonts, C. D., Melvin, S., & Eisenhauer, D. E. (2008). Predicting the Last Irrigation of the Season. UNL Extension Publications. https://extensionpubs.unl.edu/publication/g1871/html/view


Context: The description of a static VRI irrigation prescription is that this prescription stays the same or changes only a few times during the season. Considerations include that it is relatively simple to apply. Does not account for change in spatial variability over a season. Example uses include avoiding irrigation on uncrossed areas, mining differences in soil available water capacity, and variable rate chemigation.

Question: what type of irrigation system is relatively easy to apply?

Answer: static VRI irrigation prescription

Barker, J. B. (2017). Considerations in Adopting Variable Rate Irrigation for Center Pivots and Lateral Systems. http://extensionpublications.unl.edu/assets/pdf/ec2000.pdf.


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In the weighted average dry years, 2020, 2021, 2022, 64% were ranked good, 11% were fair, 3% were wet late, 15% were wet early, 3% were wet all season, and 4% were very wet all season.

Question: what percentage of Nebraska fields were wet all season in the dry years of 2020, 2021, and 2022?

Answer: 3%

Heeren, D., Barker, J. B., Lo, T. H., Melvin, S., Martin, D., & Luck, J. (2017). Considerations in Adopting Variable Rate Irrigation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/considerations-adopting-variable-rate-irrigation


Context: Calculating the amount of water needed from rain and irrigation for the crop to reach maturity becomes important after early August. The objective is to leave the field as dry as possible without lowering the yield.

Question: what is leaving the field as dry as possible without lowering the yield considered?

Answer: The objective

Melvin, S. (2019). Scheduling the Last Irrigations in a Year with Delayed Crop Maturity | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2019/scheduling-last-irrigations


Context: Using the 40% recommendation, the data shows many irrigators are applying more water late in the season than is needed. Some years, a significant rain can cause the soil to be wetter in September, but it is usually due to applying more irrigation water than needed. The data shows that in 2017, 72% of fields were over-irrigated late in the season, and even in the drought year of 2022, 36% of fields were over-irrigated late in the year.

Question: what does data show about irrigators application of water late in the season?

Answer: many irrigators are applying more water late in the season

Melvin, S. (2023b). Optimize Those Last Few Irrigations | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/optimize-those-last-few-irrigations


Context: For soybeans in the V1 1st Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.24 inches and the estimated water use during the week of June 19-25, 2023 is 1.30 inches. For soybeans in the V2 2nd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.47 inches. For soybeans in the V3 3rd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.71 inches.

Question: what was the estimated water usage for soybeans during the V1 first node crop growth stage during the week of June 12-18 in 2023?

Answer: 0.24 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: 1) Pumping Plants - Electric motors account for the majority of the pumping plants in Nebraska, about 55% according to 2013 NASS Irrigation Survey.  They are relatively maintenance free but still need to be looked over.  It is a good idea to change the oil in the unit every year.  Next, open up the junction box and make sure the connectors are tight and have a good ground.  Also check for frayed wires and damage from rodents.

Question: when checking the junction box of an electric motor what should you make sure of?

Answer: the connectors are tight and have a good ground

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2017, out of 86 reports, 28% were ranked good, 10% were fair, 13% were wet late, 13% were wet early, 22% were wet all season, and 14% were very wet all season.

Question: In 2017 out of 86 reports, what percentage of Nebraska fields were considered wet late?

Answer: 13%

Heeren, D., Barker, J. B., Lo, T. H., Melvin, S., Martin, D., & Luck, J. (2017). Considerations in Adopting Variable Rate Irrigation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/considerations-adopting-variable-rate-irrigation


Context: The categories are as follows: Good - At least one sensor out of the three depths drier than 70 cb early and one sensor drier than 70 cb on 9/15. Fair - At least one sensor drier than 70 cb early and one sensor drier than 30 cb on 9/15. Wet Late - At least one sensor drier than 70 cb early but no sensor drier than 30 cb on 9/15. Wet Early - No sensor drier than 70 cb early, but one sensor drier than 30 cb on 9/15. Wet All Season - Both sensors measuring the second and third foot not drier than 70 cb all year, but one sensor between 30 to 70 cb on Sept. 15. Very Wet All Season - Both sensors measuring second and third foot not drier than 70 cb all year and no sensor drier than 30 cb on Sept. 15.

Question: what is the criteria for a field to be considered "wet late"?

Answer: At least one sensor drier than 70 cb early but no sensor drier than 30 cb on 9/15.

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: The Extremely Dry Winter/Spring 2022-23 Leaving the soil as dry as possible without lowering yields saves money on pumping costs and leaves room to store offseason precipitation. Most years, adequate precipitation will be received from October through May to refill the soil profile on fields that were fully irrigated the previous year in the entire state. A lot of years, even in the Panhandle, the two to four inches of recharge that fully irrigated fields can hold will be received from rainfall or snowfall. In addition to financial savings, leaving the soil drier will help reduce harvest delays due to mud if rain is received in the fall.

Question: in most years when will enough precipitation be received to refill the soil profile on fields that fully irrigated the year prior?

Answer: October through May

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: 2) Pump - The pump is a piece that is sometimes overlooked.  Before you start irrigating in the spring make sure you start the dripper to get the line shaft bearings lubed.  It needs 1 gallon of drip oil for every 100 feet of depth.  Set the dripper for 1 drip every 5 seconds.  The pump can only take oil so fast and you can't over oil them.  Also make sure the dripper line is attached and the fittings are tight.

Question: why should an irrigator not over oil a pump?

Answer: The pump can only take oil so fast

Yonts, C. D., Lyon, D. J., Harveson, R. M., Hergert, G. W., Hein, G. L., & Santra, D. (2009). Producing Irrigated Winter Wheat. https://extensionpubs.unl.edu/publication/ec731/pdf/view/ec731-2009.pdf


Context: As described in the video, walking and visually observing an irrigation system when it is running often can help locate where there are mechanical causes for poor uniformity. In some cases, obvious or easily noticeable issues can be identified, such as the broken gooseneck shown in the video. However, other instances such as stuck sprinklers or clogged nozzles may be less noticeable, especially if the sprinklers are on drops in a tall crop canopy.

Question: what can an irrigator do to help locate where there are mechanical causes for poor uniformity?

Answer: walking and visually observing an irrigation system when it is running

Rudnick, D. (2016). Sprinkler Irrigation System Maintenance for Improved Uniformity and Application Efficiency | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2016/sprinkler-irrigation-system-maintenance-improved-uniformity-and-application-efficiency


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2021, out of 53 reports, 57% were ranked good, 6% were fair, 6% were wet late, 25% were wet early, 4% were wet all season, and 4% were very wet all season.

Question: In 2021 out of 53 reports, what percentage of Nebraska fields were considered wet late?

Answer: 6%

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Context: How does CornSoyWater work in the background? CornSoyWater uses crop simulation models (Hybrid-Maize for corn and SoySim for soybean) to predict crop growth, development, crop water use, and soil water balance. Based on the location of the field, the program automatically determines the weather station that is closest to the field in the weather station network, and the soil texture for the field.

Question: how does the program determine the weather station that is closest to the field in the weather station network and the soil texture of the field in question?

Answer: Based on the location of the field

Yang, H. (2017). CornSoyWater: An Online App to Aid in Irrigation Management | UNL Water. https://water.unl.edu/article/agricultural-irrigation/cornsoywater-online-app-aid-irrigation-managemen


Context: Risk of Early Season Leaching Excess irrigation has its own risks. Generally, when the soil is above field capacity, excess water leaves the root zone, called deep percolation. This is an essential function of the soil for groundwater recharge. When deep percolation takes agrichemicals past the root zone, it is called leaching. May and June are the most critical time for leaching losses all year.

Question: what months are the most critical time for leaching losses all year?

Answer: May and June

Barker, J. B. (2017). Considerations in Adopting Variable Rate Irrigation for Center Pivots and Lateral Systems. http://extensionpublications.unl.edu/assets/pdf/ec2000.pdf.


Context: The Dakota aquifer (formally called the Maha Aquifer) is by far the largest of these secondary aquifers, supplying all of the water to more than 3,400 wells in eastern Nebraska. Seventy-five percent of these wells are domestic, although in places the aquifer is capable of supplying a sufficient volume of water for irrigation and commercial use. The biggest limitation to using the Dakota aquifer is potentially high salt concentrations.  Geologists think the salty water probably moves into the Dakota aquifer from underlying rocks, a hydraulic condition that is increased by heavy pumping.

Question: what is the biggest limitation to using the Dakota aquifer?

Answer: high salt concentrations

Divine, D. (2017). An Overview of Secondary Aquifers in Nebraska | UNL Water. https://water.unl.edu/article/agricultural-irrigation/overview-seondary-aquifers-nebraska


Context: These six categories were determined because the soil water level where deep percolation losses of water and nutrients slows to a low rate in a silt loam soil is about 70 cb; thus, it is recommended to keep at least one of the sensors in the second or third foot in this range or dryer. Yield losses would not be expected until all the sensors were approaching 140 cb, making the 70 cb level very achievable without any chance of causing yield loss. Field capacity in a silt loam is about 30 cb, so the goal is not to refill the soil above this level with irrigation in the second or third foot.

Question: when will yield losses be expected?

Answer: sensors were approaching 140 cb

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: To illustrate this, let's look at some data from the Upper Big Blue NRD. The NRD requires growers in six areas that have an increased median nitrate-nitrogen level in the groundwater, to use soil water monitoring equipment in one irrigated field and report the data collected annually. Most of the producers impacted by this rule use Watermark sensors that measure soil matric potential; thus, this study has largely focused on Watermark data for easy comparison. The soils in the NRD are mostly a silt loam or similar soil texture, making the field-to-field data comparable as well. The assumption was made that the farmers using Watermark sensors would represent all irrigators in the area. To protect privacy, the NRD removes names from the information prior to group analysis; therefore, the location for each field is an unspecified area in the Upper Big Blue NRD.

Question: what soils are typical in the Upper Big Blue NRD allowing for field to field data to be compared?

Answer: silt loam or similar soil texture

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Overall, our results indicate that an electric motor running at a constant 1770 rpm will use excess energy for much of the center pivot revolution. VFD operation includes the installation of a pressure sensor somewhere on the system. The controller part of the VFD adjusts the motor speed to maintain a set pipeline pressure wherever the sensor is positioned. Some sensors are placed at the pump outlet, but if the irrigated area has a lot of topography, that position is often the worst location for the sensor.

Question: if the irrigated area has alot of topography what is the worst location to place the sensor on the VFD?

Answer: the pump outlet

Yonts, C. D., Melvin, S., & Eisenhauer, D. E. (2008). Predicting the Last Irrigation of the Season. UNL Extension Publications. https://extensionpubs.unl.edu/publication/g1871/html/view


Context: For dry edible beans in the emergence-10% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.07 inches and the estimated water use during the week of June 19-25, 2023 is 0.50 inches. For dry edible beans in the 10-50% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.07 inches.

Question: what was the estimated water usage for dry edible beans during the 10%-50% cover crop growth stage during the week of June 12-18 in 2023?

Answer: 0.07 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: The description of a dynamic VRI irrigation prescription is that it changes frequently during the season, possible for each irrigation event. Considerations include that it may be complicated and increase management efforts and that it may provide maximum gross benefit. Example uses include varying irrigation to each part of the field as needed and adjusting areas as needs change over the season as well as variable rate chemigation.

Question: what is a description of a dynamic VRI irrigation prescription?

Answer: it changes frequently during the season, possible for each irrigation even

Barker, J. B. (2017). Considerations in Adopting Variable Rate Irrigation for Center Pivots and Lateral Systems. http://extensionpublications.unl.edu/assets/pdf/ec2000.pdf.


Question: what percentage wells in the Dakota aquifer are domestic?

Answer: Seventy-five percent

Divine, D. (2017). An Overview of Secondary Aquifers in Nebraska | UNL Water. https://water.unl.edu/article/agricultural-irrigation/overview-seondary-aquifers-nebraska


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2022, out of 60 reports, 70% were ranked good, 8% were fair, 3% were wet late, 15% were wet early, 2% were wet all season, and 2% were very wet all season.

Question: In 2022 out of 60 reports, what percentage of Nebraska fields were considered very wet all season?

Answer: 2%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: OK, That is Great, But I Want to Use My End Gun. The best answer may be to just not use the end gun because of its lower uniformity and the fact that it will lower the nitrogen application rate when it comes on. However, two methods of solving this problem come to mind. The first is to purchase a variable rate injection pump and the second is, if the pivot is equipped with a computer panel, keep using the lower cost fixed rate injection pump and simply slow the pivot down when the end gun turns on.

Question: what is a solution to the problem of end gun irrigation lowering the nitrogen application rate?

Answer: purchase a variable rate injection pump

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: 1) Pumping Plants - Electric motors account for the majority of the pumping plants in Nebraska, about 55% according to 2013 NASS Irrigation Survey.  They are relatively maintenance free but still need to be looked over.  It is a good idea to change the oil in the unit every year.  Next, open up the junction box and make sure the connectors are tight and have a good ground.  Also check for frayed wires and damage from rodents.

Question: what account for about 55% of the pumping plants in Nebraska according to the NASS irrigation survey in 2013?

Answer: Electric motors

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Context: When the pumping plant is designed for a center pivot installation, the pump impeller is selected that will deliver a desired flow rate and pressure to the highest elevation in the field with all sprinklers in operation.

Question: when a pumping plant is designed for a center pivot installation what is the selected pump impeller designed to deliver?

Answer: a desired flow rate and pressure to the highest elevation in the field with all sprinklers in operation

Kranz, B. (2018). Economics of Variable Frequency Drives for Irrigation Pumps. UNL CropWatch. https://cropwatch.unl.edu/2018/economics-variable-frequency-drives-irrigation-pumps


Context: If you need a refresher on how to prime the ETgage, please view the assembly video at http://water.unl.edu/cropswater/awmdnvideos. It is a good idea to replace the green covers and white wafers on a regular basis to ensure accurate readings, so if you don't have any on hand it may be a good idea to check with your local supplier.

Question: for a refresher on priming the ETgage what should an irrigator review?

Answer: the assembly video at http://water.unl.edu/cropswater/awmdnvideos

Nygren, A. (2017). Value of Using Sensors to Manage Irrigation and Tips for Proper Installation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/value-using-sensors-manage-irrigation-and-tips-proper-installation


Context: Getting the crop off to a great start is essential for a successful season. On dry years, it is sometimes necessary to start irrigating in May and June. However, it is critical to monitor soil moisture to balance crop needs with the risk of losing nitrogen and other valuable crop inputs. Monitoring will also help prevent unnecessary irrigation expenses, and if you have a water allocation, avoid using up water that is critical for later growth stages.

Question: what is critical to monitor to balance crop needs with the risk of losing nitrogen and other crop inputs?

Answer: soil moisture

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: Soil water monitoring data is easier to analyze once the crop has taken up water at the 16- to 24-inch depth during the vegetative growth stage. This drier zone can then be monitored with sensors to see if the area gets wetter or drier. If it keeps getting drier, the irrigation system needs to keep running. However, if it starts to get wetter, then stop irrigating for a few days. Ideally, the drier zone should slowly expand deeper with the crop using most of the subsoil water by the time the crop matures. For more information on this scheduling strategy, watch the Advanced Irrigation Scheduling Techniques video.

Question: if the drier zone, 16- to 24-inches in depth keeps getting drier what should an irrigator do with the irrigation system?

Answer: needs to keep running

Yonts, C. D., Lyon, D. J., Harveson, R. M., Hergert, G. W., Hein, G. L., & Santra, D. (2009). Producing Irrigated Winter Wheat. https://extensionpubs.unl.edu/publication/ec731/pdf/view/ec731-2009.pdf


Context: Table I. Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska. For Grain Sorghum stage 6 crop stage, the stage of growth is known as half bloom, the approximate days to maturity is 34, and the water use to maturity is 9.0 inches. For Grain Sorghum stage 7 crop stage, the stage of growth is known as soft dough, the approximate days to maturity is 23, and the water use to maturity is 5.0 inches. For Grain Sorghum stage 8 crop stage, the stage of growth is known as hard dough, the approximate days to maturity is 12, and the water use to maturity is 2.0 inches. For Grain Sorghum stage 9 crop stage, the stage of growth is known as physiological maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.

Question: what is the approximate water use to maturity for grain sorghum in the stage 7 crop stage, the stage of growth that is known as soft dough?

Answer: 5.0 inches

Yonts, C. D., Melvin, S., & Eisenhauer, D. E. (2008). Predicting the Last Irrigation of the Season. UNL Extension Publications. https://extensionpubs.unl.edu/publication/g1871/html/view


Context: VFDs are electronic monitor and control systems that alter the speed of pump rotation by adjusting the frequency of the electricity delivered to the motor. It turns out that the motor cares little about what frequency the power is and the speed of the motor changes linearly with the change in frequency.

Question: what are VFDs?

Answer: electronic monitor and control systems that alter the speed of pump rotation by adjusting the frequency of the electricity delivered to the motor

Kranz, B. (2018). Economics of Variable Frequency Drives for Irrigation Pumps. UNL CropWatch. https://cropwatch.unl.edu/2018/economics-variable-frequency-drives-irrigation-pumps


Context: One visual observation of a non-functioning regulator is when water is spraying out of the side of the regulator. If you have concerns that your regulators are approaching their usable life, contact your irrigation equipment dealer to have your regulators tested.

Question: what is a visual observation that can be made of a non-operational regulator?

Answer: when water is spraying out of the side of the regulator

Rudnick, D. (2016). Sprinkler Irrigation System Maintenance for Improved Uniformity and Application Efficiency | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2016/sprinkler-irrigation-system-maintenance-improved-uniformity-and-application-efficiency


Context: Table II. Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity. For silt clay or clay, the available water in 1 foot of soil at 100% of available water is 1.6 in/ft, the available water in top 4 feet at 100% of available water is 6.4 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.6 in/ft. For fine sandy loam, silty clay loam, or clay loam, the available water in 1 foot of soil at 100% of available water is 1.8 in/ft, the available water in top 4 feet at 100% of available water is 7.2 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.9 in/ft. For sandy clay loam, the available water in 1 foot of soil at 100% of available water is 2.0 in/ft, the available water in top 4 feet at 100% of available water is 8.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 3.2 in/ft.

Question: what is the amount of available water in units of (in/ft) for sandy clay loam soil at 100% of available water in the top 4ft of soil?

Answer: 8.0 in/4 ft

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.02, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.96. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.03, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.94. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.04, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.92. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.05, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.91. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.06, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.89. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.07, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.87. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.08, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.86. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.09, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.84. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.1, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.83. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.11, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.81. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.12, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.8. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.13, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.78. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.14, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.77. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.15, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.76. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.16, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.74. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.17, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.73. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.18, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.72. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.19, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.71. When the ratio of the end gun throw (Rg) to the pivot length (R) is 0.2, the the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) is 0.69.

Question: what is the pivot speed with the end gun on (Se) compared to the speed with the end gun off (S) when the ratio of the end gun throw (Rg) to the pivot length (R) is 0.09?

Answer: 0.84

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Percent of fields that became wetter moving from August to Sept. 15. The dry years 2020, '21 and '22 fields are much drier than the other years in the fall.  In 2020, 45% of fields with soil in the 15-25 in zone became wetter from August to Sept. 15, 21% of fields with soil in the 25-36 in zone became wetter from August to Sept. 15, and 21% of fields with soil in both zones became wetter moving from August to Sept. 15.

Question: what percentage of fields with soil in the 25-36 inch zone became wetter from August to Sept. 15 in 2020?

Answer: 21%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Table I. Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska. For Dry Beans R5 crop stage, the stage of growth is known as early seed fill, the approximate days to maturity is 35, and the water use to maturity is 7.0 inches. For Dry Beans R6 crop stage, the stage of growth is known as mid-seed fill, the approximate days to maturity is 25, and the water use to maturity is 4.2 inches. For Dry Beans R7 crop stage, the stage of growth is known as beginning maturity, the approximate days to maturity is 15, and the water use to maturity is 2.0 inches. For Dry Beans R8 crop stage, the stage of growth is known as harvest maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.

Question: what is the approximate days to maturity for dry Beans R6 crop stage or the stage of growth that is known as mid-seed fill?

Answer: 25

Yonts, C. D., Melvin, S., & Eisenhauer, D. E. (2008). Predicting the Last Irrigation of the Season. UNL Extension Publications. https://extensionpubs.unl.edu/publication/g1871/html/view


Context: Strategies for Early Season Irrigation Last year's irrigation will have left the soil fairly wet compared to dryland fields. On a typical year, a silt loam soil that was reasonably well irrigated the previously year (full yield) may only hold two to four inches of water from precipitation in the non-growing season. Sandy soils will hold even less. This means most years, irrigated fields will be at or above field capacity in May, particularly in the eastern two-thirds of Nebraska.

Question: what soils will hold less water from precipitation in the non-growing season than silt loam soils?

Answer: Sandy soils

Melvin, S., Power, C., Daigh, A., & Taghvaeian, S. (2023). Early Season Irrigation During Drought. UNL CropWatch. https://cropwatch.unl.edu/2023/early-season-irrigation-during-drought


Context: The two different speeds can be achieved by a simple setup in the computer pivot panel. The degree of rotation at which the end gun turns on, the program simply slows the speed down and then returns it to the faster speed at the time the end gun turns off. The idea is that we want the pivot to cover a constant number of acres per hour. The key is to know how to calculate the slower speed.

Question: where can you set up a pivot to operate on two different speeds?

Answer: computer pivot panel

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Question: what is one solution to the problem of end gun irrigation?

Answer: keep using the lower cost fixed rate injection pump and simply slow the pivot down when the end gun turns on

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2017, out of 86 reports, 28% were ranked good, 10% were fair, 13% were wet late, 13% were wet early, 22% were wet all season, and 14% were very wet all season.

Question: In 2017 out of 86 reports, what percentage of Nebraska fields were considered wet early?

Answer: 13%

Heeren, D., Barker, J. B., Lo, T. H., Melvin, S., Martin, D., & Luck, J. (2017). Considerations in Adopting Variable Rate Irrigation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/considerations-adopting-variable-rate-irrigation


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2022, out of 60 reports, 70% were ranked good, 8% were fair, 3% were wet late, 15% were wet early, 2% were wet all season, and 2% were very wet all season.

Question: In 2022 out of 60 reports, what percentage of Nebraska fields were considered wet early?

Answer: 15%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: Applying nitrogen fertilizer or crop protection products through a center pivot is an efficient and effective method. In fact, it is a well-documented best management practice to apply nitrogen fertilizer as close to the time the corn will use it to get the most efficient use of the fertilizer. Most of the products are injected into the pivot with a fixed rate injection pump. So, how does one figure the pumping rate to set the pump at, and what about the change the end gun causes when it's turned on and off? We will discuss both challenges in this article.

Question: what is a well documented best management practice for when to apply fertilizers to corn to get the most efficient use of the fertilizer?

Answer: as close to the time the corn will use it

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Percent of fields that became wetter moving from August to Sept. 15. The dry years 2020, '21 and '22 fields are much drier than the other years in the fall.  In the weighted average normal to wet years, 2017, 2018, 2019, 65% of fields with soil in the 15-25 in zone became wetter from August to Sept. 15, 66% of fields with soil in the 25-36 in zone became wetter from August to Sept. 15, and 37% of fields with soil in both zones became wetter moving from August to Sept. 15.

Question: what percentage of fields with soil in the 15-25 inch zone and the 25-36 inch zone became wetter from August to Sept. 15 in the wet years of 2017, 2018, and 2019?

Answer: 37%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: For soybeans in the V1 1st Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.24 inches and the estimated water use during the week of June 19-25, 2023 is 1.30 inches. For soybeans in the V2 2nd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.47 inches. For soybeans in the V3 3rd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.71 inches.

Question: what was the estimated water usage for soybeans during the V1 first node crop growth stage during the week of June 19-25 in 2023?

Answer: 1.30 inches

Stone, G., & Qiao, X. (2023). Estimated Crop Water Use for June 19-25, 2023 | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2023/estimated-crop-water-use-june-19-25-2023


Context: The Extremely Dry Winter/Spring 2022-23 Leaving the soil as dry as possible without lowering yields saves money on pumping costs and leaves room to store offseason precipitation. Most years, adequate precipitation will be received from October through May to refill the soil profile on fields that were fully irrigated the previous year in the entire state. A lot of years, even in the Panhandle, the two to four inches of recharge that fully irrigated fields can hold will be received from rainfall or snowfall. In addition to financial savings, leaving the soil drier will help reduce harvest delays due to mud if rain is received in the fall.

Question: what does leaving the soil as dry as possible without lowering yields save money on?

Answer: pumping costs

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: 1) Pumping Plants - Electric motors account for the majority of the pumping plants in Nebraska, about 55% according to 2013 NASS Irrigation Survey.  They are relatively maintenance free but still need to be looked over.  It is a good idea to change the oil in the unit every year.  Next, open up the junction box and make sure the connectors are tight and have a good ground.  Also check for frayed wires and damage from rodents.

Question: what types of motors are relatively maintenance free?

Answer: Electric motors

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Context: Check for proper operation by making sure there is not any water squirting from the side of any regulators.  This is a sign that the rubber bladder has failed.  Keep in mind that sprinklers and pressure regulators do have a life span.  If your system is approaching 10 years old you might need to take a closer look at them.  Uniformity of water application can suffer greatly if your sprinkler package is out of date.

Question: if your irrigation system is approaching 10 years old what components should you take a closer look at?

Answer: sprinklers and pressure regulators

Ingram, T. (2017). Is Your Irrigation System Ready For the Season? | UNL Water. https://water.unl.edu/article/agricultural-irrigation/your-irrigation-system-ready-season


Context: Thus, the pivot should operate at a 90% timer setting when the end gun is off and slow to 77.4% when it is on to apply the 30 lbs/acre nitrogen both when the end gun is off, as well as when it is on. The water application will be different - 0.29 inches when the end gun is off and about 0.33 inches when it is on - but the nitrogen rate will remain the same with the constant injection rate pump. The concept behind this method is that the pivot will irrigate the same number of acres per hour, thus the lower cost fixed-rate injection pump will work correctly.

Question: what will remain the same if the pivot system uses a timer and there is a constant injection rate pump?

Answer: the nitrogen rate

Divine, D. (2017). An Overview of Secondary Aquifers in Nebraska | UNL Water. https://water.unl.edu/article/agricultural-irrigation/overview-seondary-aquifers-nebraska


Context: 2) Pump - The pump is a piece that is sometimes overlooked.  Before you start irrigating in the spring make sure you start the dripper to get the line shaft bearings lubed.  It needs 1 gallon of drip oil for every 100 feet of depth.  Set the dripper for 1 drip every 5 seconds.  The pump can only take oil so fast and you can't over oil them.  Also make sure the dripper line is attached and the fittings are tight.

Question: what should an irrigator check on the pump prior to irrigating to ensure they're attached and tight?

Answer: make sure the dripper line is attached and the fittings are tight

Yonts, C. D., Lyon, D. J., Harveson, R. M., Hergert, G. W., Hein, G. L., & Santra, D. (2009). Producing Irrigated Winter Wheat. https://extensionpubs.unl.edu/publication/ec731/pdf/view/ec731-2009.pdf


Context: To determine the actual cost, we would recommend the use of the IrrigateCost app. The app, which is available for both Apple and Android products, allows users to input their specific information such as acres irrigated, pumping lift, system PSI, pump and pivot life, and inches applied as well as related costs such as for the well and engine, labor, energy, district fees, and taxes. The app then calculates total irrigation cost as well as total ownership and total operating costs.  It also breaks down costs by irrigation well, pump, gear head, pump base, diesel engine and tank and system and calculates per acre annual cost and per acre-inch annual cost.

Question: what is recommended to help determine the actual irrigation cost?

Answer: use of the IrrigateCost app

Nygren, A. (2017). Value of Using Sensors to Manage Irrigation and Tips for Proper Installation | UNL Water. https://water.unl.edu/article/agricultural-irrigation/value-using-sensors-manage-irrigation-and-tips-proper-installation


Context: Whenever the crop-available soil water amount falls below the threshold for irrigation or the crop is under water stress, the program will recommend irrigation if no significant rain is expected in the next three days. The message is displayed at the top of the screen (Figure 3).

Question: when will the CornSoyWater program recommend irrigation if no significant rain is expected in the next three days?

Answer: Whenever the crop-available soil water amount falls below the threshold for irrigation or the crop is under water stress,

Yang, H. (2017). CornSoyWater: An Online App to Aid in Irrigation Management | UNL Water. https://water.unl.edu/article/agricultural-irrigation/cornsoywater-online-app-aid-irrigation-managemen


Question: what will leaving the soil drier help reduce in addition to financial savings?

Answer: harvest delays due to mud if rain is received in the fall

Melvin, S. (2023c). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Question: what is a key calculation that needs to be made to use the computer pivot panel program?

Answer: slower speed

Melvin, S. (2023a). How to Determine the Chemigation Injection Pump Setting for a Center Pivot with the End Gun Off and On. UNL CropWatch. https://cropwatch.unl.edu/2023/how-determine-chemigation-injection-pump-setting-center-pivot-end-gun-and


Context: Average percent of fields by year fitting into the six categories. The dry years 2020, '21 and '22 are different than the other years. In 2020, out of 39 reports, 64% were ranked good, 21% were fair, 0% were wet late, 3% were wet early, 5% were wet all season, and 8% were very wet all season.

Question: In 2020 out of 39 reports, what percentage of Nebraska fields were considered very wet all season?

Answer: 8%

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: One visual observation of a non-functioning regulator is when water is spraying out of the side of the regulator. If you have concerns that your regulators are approaching their usable life, contact your irrigation equipment dealer to have your regulators tested.

Question: who should you contact to have your regulators tested if you have concerns that your regulators are approaching their usable life?

Answer: your irrigation equipment dealer

Rudnick, D. (2016). Sprinkler Irrigation System Maintenance for Improved Uniformity and Application Efficiency | CropWatch | University of Nebraska–Lincoln. https://cropwatch.unl.edu/2016/sprinkler-irrigation-system-maintenance-improved-uniformity-and-application-efficiency