bluuebunny/crossref_metadata_2025 huggingface dataset:
Intensifying Plant Density Response of Corn with Artificial Shade
Authors: Hashemi‐Dezfouli A. , Herbert S. J.
Published: July 2010

Competition among corn (Zea mays L.) plants for interception of photosynthetically active radiation (PAR) at high plant density can result in a reduction in kernel number per ear and complete ear barrenness. The response of field corn to long‐term shading as density increased was investigated. A single‐ear hybrid was grown at the Agricultural Experiment Station Farm, Univ. of Massachusetts, at three densities of 3, 7.5, and 12 plants m−2. Shading was provided by using black polypropylene fabric with 50% light penetration installed 44 d after emergence. The rate of apparent photosynthesis in ear leaves was reduced significantly by both increased plant density and shading. The reduction was attributed to reduced PAR in higher densities and shaded plots and to the decreased chlorophyll concentration measured in leaves of plants at high density in both ambient light and shaded plots. Tassel emergence was slightly delayed in high density and shaded plots. However, the time of silking was delayed significantly because of both high density and shading. Seven days after anthesis, 10% of plants in high densities and 50% of plants in shaded plots had no silk. The response of grain yield per unit area in ambient light to increasing density was parabolic. No increase in yield was obtained with density increase in the shaded plots. Shade reduced the number of productive ears per plant, and the number of kernels per row resulting in a 23 and 66% yield reduction in low and high plant densities respectively, when compared to ambient light. Weight per kernel was reduced 28% with increased plant density. Shading did not further decrease kernel weight. The number of kernel rows per ear was least sensitive to both high plant density and shading.
Corn Phosphorus and Potassium Uptake in Response to Soil Compaction
Authors: Dolan M. S. , Dowdy R. H. , Voorhees W. B. , Johnson J. F. , Bidwell‐Schrader A. M.
Published: July 2010

Soil compaction by heavy axle load farm machinery can inhibit optimum plant growth. Uptake of essential nutrients, like P and K, is influenced by soil compaction. This study describes plant P and K accumulation from a compacted Webster (fine‐loamy, mixed, mesic Typic Haplaquolls) soil. Whole plant samples of corn (Zea mays L.) were collected at the 75% vegetative‐tassel (VT) stage from 0, 9, and 18 Mg axle load subsoil compaction treatments, each with secondary interrow surface soil compaction of 0‐ or 4.5‐Mg axle loads. Subsoil compaction reduced P and K uptake as much as 22% during seasons when June and July rainfall was less than average. Subsoil compaction of 18 Mg did not consistently reduce P and K uptake more than did 9 Mg subsoil compaction. Surface soil compaction also reduced P uptake, but to a lesser extent than did subsoil compaction. Overall P and K uptake, across all treatments, was enhanced when June and July precipitation was average or wetter than the 30‐yr average.
Estimation of Solar Radiation Data Missing from Long‐Term Meteorological Records
Authors: Hook J. E. , McClendon R. W.
Published: July 2010

Solar radiation has a direct effect on plant growth and, thus, is used in most crop growth models. At most locations in the USA, though these measurements have been made only in recent years. At Tifton, GA, a 53‐yr (1938–1990) record was available with meteorological observations consisting of maximum/minimum temperature, precipitation, and pan evaporation. Only during the last 15 yr was solar radiation data available. To allow us to use these data to evaluate realistic scenarios for drought occurrence studies, we developed a method to estimate daily global solar radiation. Using a 13‐yr record of meteorological observations with solar radiation, a regression equation was developed to determine daily solar radiation from maximum and minimum air temperature, pan evaporation, precipitation, and calculated extraterrestrial radiation. A random component was added to express the variability associated with the unmeasured degree of cloudiness. The radiation estimate had the same variances and means as observed data and an overall correlation of 78%. The 53‐yr record with estimated solar radiation represents an intermediate step between computer generated radiation scenarios and fully measured data. The approach presented here should help to complete long‐term weather records so that crop growth and water balance models can be applied to historical data.
A Modular Structure for Crop Simulation Models: Implemented in the SIMPOTATO Model
Authors: Hodges Tom , Johnson Scott Lee , Johnson Brad S.
Published: July 2010

A highly modular structure has been developed for crop growth simulation models and implemented in the SIMPOTATO model, a model based on the standards of the IBSNAT (International Benchmarks Sites Network for Agrotechnology Transfer) project. The model structure features top‐down design, modularity, high cohesiveness, loose coupling, and data hiding. SIMPOTATO is composed of (i) an upper level module to run the model, (ii) an experiment selection module, (iii) an initialization module, (iv) a simulator module, (v) the crop and soil processes module, (vi) a start/stop module, (vii) a report writing module, and (viii) a graphic display module. Each module is composed of one or more subroutines and functions. Such a modular structure facilitates transferring improvements between models, combining models into multi‐crop models and crop/pest models, and modifying models for new applications.
Cultural Factors for Minimizing Bermudagrass Invasion into Tall Fescue Turf
Authors: Brede A. D.
Published: July 2010

Tall fescue (Festuca arundinacea Schreb.) is becoming increasingly popular for turf in areas where bermudagrass [Cynodon dactylon L. (Pers.)] has traditionally been grown. Volunteer bermudagrass can be a serious weed problem in tall fescue lawns, and presently there are no reliable herbicides to eradicate bermudagrass without injury to the fescue. The purpose of this study was to examine multiple cultural factors to see if a combination of treatments might be used to prevent bermudagrass invasion into fescue turf. Cutting height (19 and 57 mm), fescue cultivar (‘Kentucky‐31’ and ‘Mustang’), fescue seeding rate [2100, 12 900, and 34 400 pure‐live seeds (PLS) m−2], fertilization rate (49 and 244 kg N ha−1yr−1), and source of bermudagrass introduction [seed, rhizomes, or stolons (clippings)] were examined in this 2‐yr field study performed on Kirkland silt loam soil (fine, mixed, thermic, Udertic Paleustolls) in central Oklahoma. No bermudagrass invaded plots that were seeded to the two higher fescue seeding rates and mowed at the higher cutting height. The greatest number of bermudagrass originations (6 crowns m−2) and amount of stolon coverage (42%) occurred in plots of Mustang seeded to the lowest seeding rate, mowed at the lower cutting height, and fertilized at the heavier rate, with seed as the source of bermudagrass introduction. In conclusion, if tall fescue is managed like bermudagrass turf (closer mowing, higher fertilization), then the stand may eventually give way to invading bermudagrass.
Irrigating and Liming Alfalfa on Coastal Plain Soil
Authors: Morris D.R. , Caldwell A.G. , Corkern D.L.
Published: July 2010

Alfalfa (Medicago sativa L.) stands do not persist for longer than 2 or 3 yr in many regions of the southern USA. A 3‐yr experiment was conducted to determine if alfalfa yield and stand persistence could be improved by irrigating and liming. Water management treatments were no irrigation and spinkle irrigation with about 25 mm of water when soil moisture reached approximately 50% of available water. Dolomitic lime treatments included 0 lime, 2.2 Mg lime ha−1 applied before planting, and 4.4 Mg lime ha−1 applied before planting, and 2.2 Mg time ha−1 applied every year. Soil samples were taken and analyzed for pH, exchangeable Ca, Mg, and Al and available Mn. In addition, plant density was monitored. Annual dry matter yields averaged 13, 10, and 3 Mg ha−1 in 1987, 1988, and 1989, respectively. The progressive decrease in seasonal yield over time was due to a decline in plant population density from an average of 191 to 26 plants per square meter between Years one and three of the study. Dry matter yield was not changed by irrigation, but decreased by an average of 0.9 Mg ha−1 when lime was not applied. Crop annual dry matter yield showed a positive correlation with soil Ca, Mg, and pH and a negative correlation with soil Al. Growing conditions resulting from lime application and irrigation should have been favorable for alfalfa production; therefore, stand reduction was probably not due to acid condition or drought stress in the surface soil.
Yield and Quality of Silage Corn as Altered by Johnsongrass Infestation
Authors: Mueller J. P. , Lewis W. M. , Green J. T. , Burns J. C.
Published: July 2010

Dairy and beef producers in the southern piedmont region of the USA with limited land often grow corn (Zea mays L.), after corn, for silage even though stands gradually become infested with johnsongrass [Sorghum halepense (L.) Per.]. The objective of this study was to quantify the influence of johnsongrass infestation on the yield and quality of corn grown for silage. Seven field trials were conducted over a 6‐yr period in the piedmont region of North Carolina on clayey, kaolinitic, thermic, Typic Hapludult soils. Corn was planted each year into johnsongrass‐infested sites. Herbicides were used to produce johnsongrass‐free plots and plots where johnsongrass was the only weed present. Additionally, to assess the influence of johnsongrass infestation level on the subsequent silage quality, physical mixtures of corn and johnsongrass forage were made which represented an infestation range from 0 to 100% by weight. In five of seven trials, corn forage yield was significantly increased with johnsongrass control. Where johnsongrass was not controlled, corn plant population was reduced by 13% and silage quality, estimated by in vitro dry matter disappearance (IVDMD), was reduced by 8 to 21%. Silage IVDMD decreased linearly 2.37 g kg−1 (r2 = 0.95, P < 0.001) for each percentage unit increase in johnsongrass infestation by weight.
Nitrogen Management for Spring Wheat Grown Annually on Zero‐Tillage: Yields and Nitrogen Use Efficiency
Authors: Campbell C. A. , Zentner R. P. , Selles F. , McConkey B. G. , Dyck F. B.
Published: July 2010

Soil testing laboratories require predictive equations that provide accurate fertilizer recommendations to improve economic return to producers and reduce the risk of environmental pollution. Snow management by cereal trap strips and fertilizer N management involving rates, placement, and timing of application were studied in a 9‐yr experiment on a Swinton Loam (Aridic Haploboroll) in southwestern Saskatchewan. Spring wheat (Triticum aestivum L.) was grown annually using zero‐tillage management. Stepwise regression with backward elimination was used to develop the following relationship: Y = −781 + 3.11 WU + 6.88 FN − 0.053 FN2 − 0.33 SN2 + (0.23 SN × WU) − (0.25 SN × FN) + (0.035 FN × WU) + (0.00083 SN × FN × WU) + (1.60 Yr × SN) − (0.53 Yr × FN) R2 = 0.91, P=0.001, n = 1248), where Y = grain yield (kg ha−l), WU = estimated water use (mm), SN = available soil N (kg ha−1), FN = rate of fertilizer N (kg ha−1), and Yr = number of years of study. Water use was available spring soil water in the 0‐ to 1.2‐m depth plus 1 May to 31 July precipitation, and SN was NO3‐N in 0‐ to 0.6‐m depth, measured in the fall. The regression accurately predicted yields of wheat for an 8‐yr zero‐tillage study carried out on similar soil nearby. Fertilizer N placement (seed placed, deep band, broadcast) influenced grain yields more than timing, but in 5 of 9 yr neither factor was significant. Response to fertilizer N decreased with years, presumably because the available N supplying power of the soil improved under no‐till management with adequate fertilization. Efficiency of available N use [grain wt/(SN + FN)] varied from 4 to 41 kg grain kg−1 N, being directly related to WU and generally to SN, but inversely to FN rate.
Use of Stability Analysis for Long‐Term Soil Fertility Experiments
Authors: Raun W. R. , Barreto H. J. , Westerman R. L.
Published: July 2010

Long‐term fertility experiments with replications are often statistically analyzed as split plots in time. Years are often shown to be significantly different and the inconsistency of treatment effects over years enters into significant year‐by‐treatment interactions which are difficult to interpret. The objectives of this study were to evaluate long‐term fertility experiments by stability analysis and relative stability and to observe possible benefits of these analyses to complement conventional analysis of variance procedures. Stability analysis which is the linear regression of treatment yield on the location/year environment mean yield was performed on long‐term wheat (Triticum aestivum) and corn (Zea mays L.) fertility trials. Stability analysis on wheat data from the Magruder Plots, indicated that beef manure applications (269 kg N ha−1) responded poorly compared to the NPK treatment when environment means were low (<2.0 Mg ha−1) and visa versa when environment means were high (>2.0 Mg ha−1)‐ Similarly, anhydrous ammonia applied as sidedressing in an irrigated corn experiment at Mead, NE, was found to be superior to urea‐ammonium nitrate applied either pre‐plant or sidedressed when environment means were less than 8.0 Mg ha−1. Stability analysis provided a simple method of interpreting significant year‐by‐treatment interactions detected in analysis of variance models from these longterm experiments. Stability analysis may also be useful for multilocation experiments and continuous site experiments where treatments are applied to the same plot year to year. However, stability analysis may be misleading when employed on continuous site experiments where autocorrelations are present year to year.
Cool Night Temperatures Alter Leaf Starch and Photosystem II Chlorophyll Fluorescence in Cotton
Authors: Warner Donn A. , Burke John J.
Published: July 2010

Cotton (Gossypium hirsutum L.) growth and reproduction are sensitive to cool temperatures, but few studies are available on specific metabolic responses to low temperature stress. We studied the relationship between starch levels and Photosystem II (PSII) function in cotton plants grown in growth chambers to determine if low temperature stress at night alters metabolic processes during the day when temperatures are optimal. Predawn starch levels in fully expanded leaves were three to four times higher on an area basis, and PSII chlorophyll fluorescence was 43 to 54% lower in leaves of two varieties of cotton (T25 and Paymaster HS26, averages for three plants of each variety) when grown with a day/night temperature of 28/20 °C, compared with plants grown at a constant temperature of 28 °C. Cotton plants that were grown at a constant 28 °C had 4.4 (T25, n = 3) to 6.6 (HS26, n = 3) times more starch on a leaf‐area basis after exposure to one night at 20 °C. When cotton plants that were grown with a day/night temperature of 28/20 °C were exposed to one night at 28 °C, starch was depleted to levels found in control plants that were grown at a constant 28 °C. The response of chlorophyll fluorescence was reciprocal to that of leaf starch when night temperature was changed. Shading, to reduce starch in six plants of each variety grown with 20 °C night temperatures to levels found in plants grown with 28 °C night temperatures, resulted in increased PSII chlorophyll fluorescence of 200%. We conclude that a night temperature of 20 °C caused an accumulation of leaf starch that was associated with reduced PSII function, even when plants experienced optimal temperatures during the day.
Defoliation and Plant Density Effects on Maize Selected for Reduced Plant Height
Authors: Edmeades G. O. , Lafitte H. R.
Published: July 2010

Selection for reduced plant height in maize (Zea mays L.) has been accompanied by a reduction in stem volume and in stem nonstructural carbohydrate (SNSC) reserves, which may result in increased instability of grain yield when plants are exposed to stress during grain filling. This possibility was examined when cycles 0, 6, 12, and 18 of a tropical maize population selected recurrently for reduced height were grown in four environments at 3.5 and 6.7 plants m−2 and defoliated by removing all but five, all but three, or no leaves 7 d after 50% silking. Per‐cycle changes were observed in undefoliated plots for stem biomass (−0.116 Mg ha−1), grain yield (0.052 Mg ha−1), optimum plant density for grain yield (0.14 plants m−2), and harvest index (0.009). Lodging declined from 39 to 10% with 18 cycles (C18) of selection. The reduction in SNSC in C18, compared with C0, was 0.66 Mg ha−1. Defoliation increased the per‐cycle reduction in final stem biomass to −0.146 Mg ha−1, but reduced grain yield and harvest index equally in all cycles of selection. At 7 d after silking, SNSC was correlated with final plant height (r = −0.66**, 16 df) and with final kernel number per plant (r = 0.48*, 16 df). Reduction in plant height increased stability of grain yield by reducing lodging and by increasing tolerance to stresses occurring near flowering.
Aluminum Effects on Calcium Uptake and Translocation in Wheat Forages
Authors: Huang J. W. , Grunes D. L. , Kochian L. V.
Published: July 2010

The effects of Al on Ca transport could influence Ca accumulation in plants. Low forage Ca concentrations may cause hypocalcemia, a Ca deficiency syndrome of ruminants. Solution culture experiments were conducted in a growth chamber to examine the effects of Al (5–50 μM on uptake and translocation of Ca (45Ca) in winter wheat (Triticum aestivum L.) cultivars (Al‐tolerant Atlas 66 and Al‐sensitive Scout 66). Three‐day‐old seedlings, grown either in a CaCl2 solution (0.1 or 1.0 mM) or in a complete‐nutrient solution, were used. For plants grown in CaCl2 solution, addition of 5 μM Al significantly decreased Ca uptake and translocation in Scout 66, but not in Atlas 66. Higher levels of Al (20 and 50 μM) decreased Ca uptake and translocation much more in Scout 66 than in Atlas 66. For plants grown in complete‐nutrient solution, Al (5–50 μM) exposure for up to 6 h had little effect on Ca uptake and translocation in either cultivar. This may be due to the reduction in Al3+ activities in the external solution, as well as lowered Al3+ activities near the root‐cell plasmalemma. When roots were exposed to Al for 24 h, Ca uptake and translocation were decreased significantly in Scout 66, but were little affected in Atlas 66. The percentage of Ca translocated to the shoots was significantly decreased by Al in Scout 66, but not in Atlas 66. These results suggest that Al inhibits both Ca uptake and translocation in Scout 66, but inhibits primarily root Ca uptake in Atlas 66 (and only at higher Al levels). It appears that the use of Al‐tolerant cultivars of wheat forages on acid soils could be important for maintaining proper Ca nutrition of grazing animals.
Minirhizotron Wheat Root Data: Comparisons to Soil Core Root Data
Authors: Box J. E. , Ramsuer E. L.
Published: July 2010

A nondestructive, quick, and efficient root measurement technique that quantifies root dynamics is critical to understanding environmental effects on rooting. The objective of this study was to compare roots of three cultivars of soft red winter wheat (Triticum aestivum L.) observed in minirhizotrons with those washed from soil cores. Minirhizotron determinations were root count (Ca, count cm−2) and root length (La, cm cm−2) per unit area; soil core determinations were root length (Lv, cm cm−3) and root dry weight (Wv, mg cm−3) per unit volume. Growth stages studied were double ridge, early boot, milk, and soft dough. Analysis of variance showed that growth stage and soil depth were significant for Lv, Wv, Ca, and La. Cultivar was significant at early boot and milk growth stages for Ca. Linear regression of Lv, Wv or La as a function of Ca provided highly significant slope and, except for Wv, intercept values. Statistically, Ca was the most discriminating minirhizotron measurement parameter.
Growth and Nutrient Uptake Parameters in Sorghum as Influenced by Aluminum
Authors: Baligar V. C. , Schaffert R. E. , Dos Santos H. L. , Pitta G. V. E. , De C. Bahia Filho A. F.
Published: July 2010

Sorghum[Sorghum bicolor (L.) Moench] is the fifth most important cereal crop in the world. The majority of soils on which sorghum is grown are acidic, and production on such soils is limited by high levels of Al and Mn, and deficient levels of Ca, Mg, and P. A greenhouse experiment was conducted to evaluate differences in growth and uptake (U), influx (IN), and transport (TR) of nutrients by 40 sorghum genotypes at three levels of soil Al saturation. Growth of shoots and roots and nutrient uptake parameters were affected by soil Al saturation, genotypes, and their interactions. Growth and uptake parameters were used to separate the genotypes into most efficient and least efficient categories at various levels of soil Al saturation. Shoot nutrient U, IN, and TR were positively correlated (P < 0.01) with shoot and root dry weight, and inversely related (P < 0.01) to soil Al saturation and shoot Al concentration. Our greenhouse technique appears to be a reliable method for separating genotypes into Al‐tolerant and intolerant types. Genotypes used in the study showed intraspecific genetic diversity in growth and uptake, influx, and transport of essential elements. Therefore, selection of acid‐tolerant genotypes and further breeding of Al‐tolerant cultivars is feasible in sorghum.
Forage Legume Roots and Nodules and Their Role in Nitrogen Transfer
Authors: Dubach Markus , Russelle Michael P.
Published: July 2010

Legumes can transfer significant amounts of symbiotically fixed N to neighboring plants, and a putative pathway for N transfer is decomposition of fine roots (those that are not secondarily thickened) and nodules. Our objective was to quantify the amount of N in living and dead roots and nodules of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). These values were used with estimates of root length and nodule numbers that decomposed during a season to estimate the size of this pathway of N transfer. Birdsfoot trefoil and effectively and ineffectively nodulated alfalfa were grown in root observation boxes filled with 15N‐labeled topsoil (Typic Hapludolls). Roots and nodules were removed according to age and analyzed for total N and C. Specific N content of fine roots older than 2 wk was 0.22 mg N m−1 in alfalfa and 0.14 mg N m−1 in trefoil, and did not change with age. Specific N content did not decline in dead, nondecomposed roots of N2‐fixing plants, indicating either that no significant N remobilization occurred or that N import equaled N export in these organs. Large, active birdsfoot trefoil nodules (>2 mm) had twice the N content of large active alfalfa nodules. Dead nodules, observed in birdsfoot trefoil only, had significantly lower N content than live nodules, indicating N remobilization during senescence. Fine roots contained up to 69% of N from fixation in alfalfa and 47% in birdsfoot trefoil, and nodules contained 89% and 94% fixed N, respectively. We conclude that alfalfa releases more N through decomposing roots than nodules, whereas birdsfoot trefoil contributes more N to the soil through decomposing nodules than roots, but neither process could account fully for published estimates of N transfer.
The ALFALFA CATALOG Software Package
Authors: Townsend M. S. , Henning J. A. , Currier C. G.
Published: July 2010

Due to modern plant breeding methods, agricultural producers have many cultivars available for many different species. Consequently, it is often difficult to recommend a cultivar for a particular growing area. A list of alfalfa cultivars, germplasms, and breeding lines available was published. However, due to the large number of entries in these publications finding pertinent information about a cultivar, breeding line, or germplasm was tedious. The objectives of this project were to (i) develop a computer program to access the alfalfa information in the original database, and (ii) update the database to include those alfalfa cultivars, breeding lines, and germplasms released through late 1992. A computer program was written using Microsoft QuickBasic, ver. 4.5. The original alfalfa database was converted to ASCII format. The resulting software package is entitled the ALFALFA CATALOG ver. 1.0. Three program files and four data files comprise the ALFALFA CATALOG software package. Users may rapidly search the database and retrieve entries by cultivar name, experimental designation, or germ‐plasm. We also wrote a routine to print a list of all cultivars or germplasms that have a specific combination of traits. These search capabilities will allow plant breeders, extension agents, and consultants rapid access to pertinent alfalfa data. Currently, the ALFALFA CATALOG has 752 entries for cultivars and breeding lines, and 144 entries for germplasms. The database will be updated yearly. In its present form, the ALFALFA CATALOG is probably the most complete compilation of alfalfa cultivars, breeding lines, and germplasms available.
Reflood Timing for Ratoon Rice Grown on Everglades Histosols
Authors: Coale F. J. , Jones D. B.
Published: July 2010

Rice (Oryza sativa L.) ratooning is commonly practiced in the Everglades Agricultural Area of southern Florida, yet optimum length of the drained period between main and ratoon crops has not been determined. Research was conducted to determine the effect of length of drain period at main‐crop harvest on ratoon rice productivity on an Everglades Histosol. Our research was conducted in 250‐L (0.95 m height, 0.58 m i.d.) custom‐made water control lysimeters filled with a Pahokee muck soil (euic, hyperthermic Lithic Medisaprist). Ratoon reflood timing treatments were 0, 5, 15, 25, 35, and 45 d drained beginning at maincrop maturity. Ratoon‐crop grain yield exhibited a significant quadratic response to length of drain period with maximum grain yield produced at 28 d drained. Ratoon panicle number was not affected by reflood timing, but quadratic responses to length of drain period were observed for grain number and 1000‐grain weight. We propose that the resultant effect of reftood timing on ratoon grain yield was the combined responses to increasing mineral N supply and increasing water stress associated with delayed reftooding. For drained durations =28 d, the beneficial effects of increased mineral N supply resulting from organic matter oxidation resulted in a net increase in ratoon‐crop yield. Conversely, for drained periods >28 d, the detrimental impact of prolonged water stress dominated the response to reflood timing and ratoon rice yields declined.
Fenarimol Tolerance of Roughstalk Bluegrass Overseeded in Bermudagrass Greens
Authors: Johnson B. Jack
Published: July 2010

Bermudagrass (Cynodon spp.) putting greens are overseeded with cool‐season grasses in the fall to maintain a high‐quality putting turf throughout the southern USA. Perennial ryegrass (Lolium perenne L.) has been the predominant grass used for overseeding until recently, when roughstalk (Poa trivialis L.) has been increasingly used for overseeding. Annual bluegrass (Poa annua L.) is a problem winter annual weed that infests most overseeded bermudagrass greens and the weed must be controlled with a herbicide to maintain a high‐quality putting surface. Fenarimol [ɑ(2‐chlorophenyl)‐ɑ‐(4‐chlorophenyl)‐5‐pyrimidinemethanol] has preemergence herbicidal activity on annual bluegrass, but it may also reduce the germination and establishment of roughstalk bluegrass seedlings. A field experiment was conducted over a 2‐yr period to determine the time interval of fenarimol treatments necessary to avoid injury to roughstalk bluegrass overseeded on a bermudagrass green. Overseeded roughstalk bluegrass tolerated fenarimol when applied as (i) a single application at 2.7 kg ha−1, (ii) two applications of 2.0 kg ha−1 each, and (iii) three applications of 1.4 kg ha−1 each, provided the final application was made ≥ 2 wk before overseeding. Quality and density of roughstalk bluegrass were not influenced by fenarimol, provided the last application was made ≥ 2 wk before overseeding in 1991 and ≥ 1 wk before overseeding in 1992. When the final fenarimol application was made during this period, the transition of overseeded roughstalk bluegrass back to bermudagrass was not affected the following spring and early summer.
Climate Change and Large‐Area Corn Yield in the Southeastern United States
Authors: Stooksbury D. E. , Michaels P. J.
Published: July 2010

There is concern about the negative effects that a possible trace‐gas‐induced climate change will have on crop yields. This study determines the effect of climate change already observed on large‐area corn yield (Zea mays L.) in the southeastern USA. Our multiple regression models differ from most previous large‐area models in two important respects. First, we modeled simultaneously the technological trend and the climate. This is required because of the warming of Southeastern nights during the past 50 yr. Second, we used maximum and minimum temperatures, rather than average temperature. Our results generally associate yield reductions with increases in daytime temperatures during the month of corn pollination. In the Middle and Upper South, increased yield is associated with warming of nighttime temperatures during mid‐season. A trace‐gas‐induced warming should produce minimal change in maximum temperatures. Because projections of future climate generally indicate more night warming than day warming, our results argue that Southeastern corn yield will either change very little or may increase slightly beyond the increase normally expected from technological advancement.
Soybean Leaf Gas‐Exchange Responses to Carbon Dioxide and Water Stress
Authors: Allen L. H. , Valle R. R. , Mishoe J. W. , Jones J. W.
Published: July 2010

As global carbon dioxide concentrations rise, we need to understand the combination of direct effects of this gas and the anticipated effects of climate change, including drought, on physiology and growth of all crops. Effects of CO2 on plants begin at the leaf level; our objectives, therefore, were to determine interrelationships among factors governing gas exchange responses of soybean [Glycine max (L.) Merr.] leaves to elevated CO2 and water stress. Photosynthetic CO2 assimilation and transpiration rates were measured in cuvettes on leaflets of soybean (cv. Bragg) grown in controlled‐environment chambers at 330 and 660 μmol CO2 mol−1 air. Leaflets at high CO2, either water‐stressed or wellwatered, had higher photosynthetic and lower transpiration rates, and therefore higher water‐use efficiencies (WUE), than those at control CO2 levels. As irrigation was withheld during an ll‐d period, WUE decreased about 30 to 50% with respect to the well‐watered treatments. Midday leaf temperature and leaf‐to‐air vapor pressure gradient levels increased as the water stress progressed. For water stress treatments, midday leaf conductance (Gtw) was generally higher and residual internal conductance (Gr) was generally lower in low than in high CO2. Ratios of midday Gr/Gtc were nearly constant throughout the period in both the stressed and the well‐watered treatments. The ratios of intercellular Ci, to ambient Ca, CO2 concentration (i.e., Ci/Ca) during the water stress period remained similar to the respective nonstressed treatments within each CO2 level. These findings support the concept that leaf conductances are governed by CO2 assimilation rates under water‐stressed as well as unstressed conditions.
Herbage and Seed Production of Annual Lespedezas as Affected by Harvest Management
Authors: Davis David K. , McGraw Robert L. , Beuselinck Paul R.
Published: July 2010

Striate [Kummerowia striata (Thunb.) Schindler] and korean [K. stipulacea (Maxim.) Makino] annual lespedezas are warm‐season forage legumes grown throughout the southeastern USA for pasture, hay, or seed. They provide high quality herbage during midsummer, when grasses often have poor quality. Limited information is available on harvest management for herbage and seed yield of annual lespedezas. The objective of this study was to determine the effect of cutting height and frequency on herbage production and seed yield of striate and korean annual lespedeza. Two field experiments were performed. The first determined the effects of a one‐ or two‐harvest management system and cutting initially at either 6 or 12 cm above the soil surface on herbage and seed yields. The second experiment was a growth analysis of lespedeza on plots not cut or cut at either 6 or 12 cm above the soil. Maximum herbage accumulation occurred for both species during late August, at ≈ 30% bloom. Harvesting in late August in the one‐harvest management system, yielded more total herbage than harvesting in July and October in the two‐harvest management system. Maximum seed yields were obtained when Marion and Summit were harvested only once in October (1115 kg ha−1 and 751 kg ha−1 of seed, respectively). Cutting height affected Summit more than Marion. Cutting Summit at a stubble height of 6 cm in July reduced both regrowth herbage and seed yields more than cutting at 12 cm. Marion regrowth herbage and seed yields were unaffected by initial cutting height. Growth habit differences between Marion and Summit were probably responsible for differences in response to cutting height. Marion is more prostrate than Summit and thus had more herbage below the cutting height after harvest to provide energy for regrowth.
Soil Compaction and Root Growth: A Review
Authors: Unger Paul W. , Kaspar Thomas C.
Published: July 2010

Adverse effects of soil compaction on crop production have been recognized for many years. The objectives of this report were to briefly review the early literature, review the contributions of Dr. Howard M. Taylor (1924–1991) and co‐workers, examine the current status of soil compaction and root growth research, and identify research needs related to soil compaction and root growth. Early in his career, Dr. Taylor and co‐workers established relationships among soil strength, soil water content, and seedling emergence and root growth. These studies showed that root growth and distribution were altered to the point that water and nutrient uptake, and, hence, plant growth and yield, were reduced when soil strength reached critical levels due to natural or induced compaction. That research formed the basis for our current knowledge concerning the effects of compaction on root growth and the alleviation of compaction through soil and tillage management. Usually, not all parts of a root system are equally exposed to compaction under field conditions. Hence, because of compensatory growth by unimpeded parts of the system, only the distribution and not the total length of roots may be altered. Even if compaction limits root growth, weather events sometimes enhance or diminish the effect of root limitation on crop growth. To reduce risks in dry years and to use applied nutrients efficiently, managing soils through the use of tillage and related practices and growing of deep‐rooted crops in rotations will help avoid or alleviate compaction, thus improving root distribution and increasing rooting depth.
Calculation of Optimal Nitrogen Fertilizer Rates
Authors: Bullock David S. , Bullock Donald G.
Published: July 2010

Agronomists sometimes fail to apply sound economic theory when recommending economically optimal nitrogen fertilizer application rates. Producers' objectives, producers' attitudes toward risk, and the effect of N on second and higher moments of the yield distribution are often left unstated or ignored. If a farmer knew, prior to N application, the future values of all stochastic factors that affect yield response to N during the growing season, optimal N rates could be established for each individual site‐year. However, farmers do not have perfect knowledge, so recommended rates should not change from year to year for a given site. We propose a more economically sound method for deriving economically optimal N fertilizer application rate recommendations. Our method maximizes profit on average over observed years for a given site. Long‐term field experiments from Illinois demonstrate that our proposed method increases profit from a trivial $0.18 ha−1 yr−1 to a substantial $103.41 ha−1 yr−1, depending on site and cropping sequence. We call for increased collaboration among agronomists and agricultural economists in the economic analysis of fertilizer application.
Predicting Daily Mean Soil Temperatures in the EPIC Simulation Model
Authors: Potter Kenneth N. , Williams Jimmy R.
Published: July 2010

Soil temperature is an important component of crop simulation models, because it affects crop growth and development, nutrient cycling, and, in some cases, water infiltration. This study was conducted to determine the efficacy of the EPIC (Erosion/Productivity Impact Calculator) mean soil temperature model and to evaluate the Parton mean surface temperature model developed for a shortgrass steppe in an agricultural simulation model. Simulated mean daily 0.05‐m soil temperatures were compared with measured mean daily 0.05‐m soil temperatures from three locations (Bushland, TX; Boone, IA; and Mandan, ND) for a range of residue management practices. The EPIC model simulated mean 0.05‐m soil temperature trends, although the predicted temperature lagged measured temperatures by 3 to 5 d, and the predicted temperature oscillations were dampened compared with the measured temperatures. The Parton model followed the mean daily temperature oscillations, but generally overestimated early spring mean soil temperatures. Simple adjustments to both models greatly enhanced temperature predictions.
Applications of Stability Analysis for Single‐Site, Long‐Term Experiments
Authors: Guertal E. A. , Raun W. R. , Westerman R. L. , Boman R. K.
Published: July 2010

Stability analysis, which is the linear regression of treatment yield on the environmental mean yield, has been proposed for use in singlesite, long‐term experiments (treatments applied to the same plots year after year), without first determining if treatment yield reveals a significant relationship with year (experiment years plotted sequentially in time). This research was initiated to demonstrate potential problems associated with stability analysis on long‐term, wheat fertility experiments where treatment yield may be correlated with year. Three single‐site, long‐term experiments were evaluated using stability analysis and linear regression of treatment yield on year. Each study was a replicated, longterm, continuous winter wheat (Triticum aestivum L.) fertility experiment, receiving annual rates of N, P, and K fertilizer. Of the single‐site, long‐term trials evaluated, one was not suitable for stability analysis, as grain yield decreased significantly with each ensuing year that the experiment was conducted. In this case, a negative residual yield response was noted with time (year) in plots receiving N and no P. Therefore, the environmental mean in stability analysis no longer reflected the random influence of climate (e.g., low and high rainfall or temperature) which could be used to decipher variable treatment response in seasonably wet or dry years. Without prior evaluation of the relationship between treatment yield and year in single‐site, long‐term experiments, stability analysis can be inappropriate.
Defoliation Effects and Seed Yield Components in Pearl Millet ✕ Elephantgrass Hybrids
Authors: Diz Diego A. , Schank Stanley C. , Wofford David S.
Published: July 2010

Prior to widespread use of seeded hybrids of pearl millet ✕ elephantgrass [Pennisetum glaucum (L.) R. Br. ✕ Pennisetum purpureum Schumach.], management to permit mechanical seed harvesting must be developed. Extreme panicle height and high biomass complicate this procedure. Defoliation management is a potential solution. This field study was conducted on a Mulat sand (sandy, siliceous, thermic Arenic Ochraquults) to (i) evaluate the effects of three defoliation treatments on height of panicles, days to flowering, seed yield components, seed yield, seed germination, and plant survival in four hybrid genotypes and (ii) evaluate the associations among seed yield components under these defoliation treatments through the use of path‐coefficient analysis. In the defoliation treatments, plants were cut zero, two, and three times per year at a 30‐cm stubble height, both in 1991 and 1992. Linear effects of defoliation accounted for 18 to 90% (1991) or 18 to 96% (1992) of the total variation in the characteristics studied. Genotype ✕ treatment ✕ year interactions were common. Panicle height and plant biomass were drastically reduced with two and three cuts per year. Defoliation delayed flowering. Two cuts per year (mid‐June and early August) did not decrease seed yield and seed quality significantly, nor did they affect plant survival Three cuts per year (the last in mid‐September) drastically reduced seed production and seed quality. Path‐coefficient analyses gave significant defoliation treatment and year effects in all traits. Seeds per panicle was always highly correlated to seed yield per plant, due to high positive direct effects and relatively low indirect effects through the other components. Defoliation altered the correlational structure among seed yield components and the compensatory mechanisms among them, but adequate seed production was maintained with two cuts per year.
From Cell Growth to Leaf Growth: III. Kinetics of Leaf Expansion
Authors: Arkebauer Timothy J. , Norman John M. , Sullivan Charles Y.
Published: July 2010

Plant growth models have, in general, not considered the detailed aspects of cell expansion and cell division. A key benefit gained by considering growth from a cellular perspective is a more thorough understanding of the role of water relations and plant growth. The objective of this research was to simulate leaf expansion in monocots using a model that incorporates cell division and cell expansion. The core of the model is a module that couples cell division and cell expansion. Assumptions are made concerning the arrangement within the leaf of the cells produced by the cell growth module. Inputs to the model include the total water potential external to the cells and the temperature of the cells. The effects of varying these input parameters on the model outputs (leaf length, leaf area, cell number, elongation rate, and meristem dimensions) are studied. The output is fairly sensitive to the water potential inputs and somewhat less sensitive to the temperature input. These sensitivities are discussed in relation to leaf expansion in field‐grown maize (Zea mays L.) plants under well‐watered and water‐limiting conditions. An extension to the model is described wherein a simple mass balance is calculated on the amount of C produced by the mature portion of the leaf and the amount of C used in the expanding portion.
A Review of Livestock Grazing and Wheat Grain Yield: Boom or Bust?
Authors: Redmon Larry A. , Horn Gerald W. , Krenzer Eugene G. , Bernardo David J.
Published: July 2010

Winter wheat (Triticum aestivum L.) grown as a dual‐purpose crop is a unique and economically important resource, especially in the southern Great Plains. Since the last major review of grazing effects on grain yield, in 1956, wheat cultivars have been developed that may affect the productivity of the grazing‐grain enterprise. Thus, we decided to review current research on grazing winter wheat and the effects on grain yield in light of earlier information. During a year of favorable precipitation and adequate to excess soil fertility, tall winter wheat cultivars grazed prior to jointing experienced increased grain yield relative to nongrazed wheat, because of reduced lodging. Current research suggests that the grain yield of semidwarf wheat cultivars is more sensitive to forage removal than for tall cultivars. Grazing termination dates necessary to prevent grain yield reduction of semidwarf cultivars also appear to be much earlier than for taller wheat cultivars. The reason for the difference in grazing tolerance is not clear; however, research suggests that semidwarf cultivars require maximum leaf area at anthesis for maximum grain yield. Tall wheat cultivars are not affected in the same manner, and decreased leaf area due to later grazing does not reduce grain yield of taller wheat cultivars to the same extent as for the semidwarf cultivars. Thus, taller wheat cultivars have the potential for extending the grazing period for livestock producers while producing grain yield similar to that of semidwarf wheat cultivars (which generally produce more grain in a nongrazed situation).
Pooling Experiments Over Time to Quantify the Dynamics of Dryland Winter Wheat Yield Response
Authors: Burt Oscar R.
Published: July 2010

This research had a dual purpose: (i) statistical estimation of winter wheat (Triticum aestivum L.) yield response as a function of plant available water and applied N fertilizer from an 8‐yr experiment in north‐central Montana and (ii) illustration of the modeling methods that are appropriate in this type of research. Summer‐fallowed and re‐cropped treatments were pooled to obtain an indirect estimate of the extra amount of N made available by summer fallow, as well as to improve the implicit experimental design by providing the necessary variation in plant available water, particularly soil water at seeding. The statistical model was nonlinear regression with an error components disturbance term entering multiplicatively. A new flexible functional form is presented for crop response; it is a polynomial generalization of the Mitscherlich single‐factor equation. A major task was to validate the regression model by considering various types of specification errors, such as accounting for all concomitant factors associated with pooling the experiments over time. Mineralized N during summer fallow was found to be a negatively sloped linear function of precipitation during the fallow period; the average amount was 24.5 kg ha−1. Nitrogen and water have strong interactions in shaping the yield response surface, and at high levels of both factors, more of either depresses yield. The depressing effect of N on yield at very low levels of water was clearly discerned.
Sod Regrowth of St. Augustinegrass after Preemergence Herbicide Application
Authors: McCarty Lambert B. , Porter D. Wayne , Colvin Daniel L.
Published: July 2010

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] sod production involves stolon regeneration from strips left from the previous harvest. Field studies were conducted to evaluate stolon regrowth and rooting following preemergence application of herbicides. Herbicides evaluated were atrazine [6‐chloro‐N‐ethyl‐N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], dithiopyr [S,S‐dimethyl 2‐(difluoromethyl)‐4‐(2‐methylpropyl)‐6‐(trifluoromethyl)‐3,5‐pyrldinecarbothioate], isoxaben [N‐[3‐(1‐ethyl‐l‐methylpropyl)‐5‐isoxazolyl]‐2,6‐dimethoxybenzamide], metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetarnlde], oxadiazon [3‐[2,4‐dichloro‐5‐(1‐methylethoxy)phenyl]‐5‐(1,1‐dimethylethyl)‐1,3,4‐oxadiazol‐2‐(3H)‐one], pendimethalin [N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine] and the combination of metolachlor plus atrazine. Acceptable ‘Floratam’ St. Augustinegrass color was noted following all treatments. Twelve to 24% of the stolons were unrooted 4 to 8 mo after application following treatment with 0.8kg a.i. ha−1 dithiopyr. Five to 22% of the stolons were unrooted 8 mo after treatment with isoxaben at 1.1 kg ha−1 and pendimethalin at 2.2 kg ha−1. Data collected after 8 mo showed stolon rooting to be similar to the untreated for all treatments. Turfgrass density was unaffected or slightly improved (≈25%) by herbicide treatment and was highest with oxadiazon, metolaehlor, and metolachlor plus atrazine treatments. Neither turfgrass tensile strength nor root dry weight was reduced 14 mo after treatment with any of the herbicides evaluated. Although shortterm (2 to 4 mo) negative effects followed dithiopyr, isoxaben, and pendimethalin treatments, long‐term (≥ 8 mo) effects were transient.