bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Use and Yield of Dryland Row Crops as Affected by Tillage
Authors: Norwood Charles A.
Published: July 2010

The dryland winter wheat (Triticum aestivum L.)‐grain sorghum [Sorghum bicolor (L.) Moench]‐fallow rotation is suitable for large areas of the U.S. Great Plains. High temperatures and potential evapotranspiration limit the number of other crops that can be grown. Sunflower (Helianthus annuus L.) is drought tolerant, but crops such as corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are perceived to lack sufficient heat and drought tolerance for semiarid areas. A study was conducted near Garden City, KS, from 1991 through 1995 to compare yield and water uses of conventional tillage (CT) and no tillage (NT) corn, grain sorghum, sunflower, and soybean to determine if crops other than grain sorghum are suitable for dryland production. Conventional tillage (CT) and no tillage (NT) were included in a wheat‐row crop‐fallow rotation. Corn and soybean were similar in their depletion of soil water, as were sorghum and sunflower. Below a depth of 1.2 m, sorghum and sunflower removed the most water. Sunflower removed the most water from the last 0.3 m of the profile and probably removed deeper water. Sorghum and sunflower removed an average of 19 mm more water from the 1.8‐m soil profile than did corn and soybean. No‐till increased yields of corn in 3 yr, of sorghum and sunflower in 2 yr, and of soybean in 1 yr. Corn had the greatest yield response to NT, averaging 31%. Average yields of corn were 25% higher than sorghum yields, whereas average yields of sunflower were 83% higher than soybean yields. Other crops can be successfully grown in the wheat‐row crop‐fallow rotation, but sorghum should occupy the most acres until the other crops have been tested under different climatic conditions.
Quantitative Color Image Analysis of Agronomic Images
Authors: Ewing Robert P. , Horton Robert
Published: July 2010

Many kinds of information that are available to our eyes in a qualitative sense require large investments of time and instrumentation to confirm quantitatively. If this information is accessible to our eyes, however, it should be possible to capture it in a color photograph and analyze it quantitatively. Our objective was to develop and make available software for enhancing and extracting quantitative information from color images. The resulting programs allow researchers to readily obtain quantitative data from color images such as photographs of plant canopies or soil with dye. The programs run in DOS and require only 512 kB of RAM, but can handle images up to 16 380 pixels across and 65 535 pixels down. The programs are designed to assist in developing an equation relating an independent parameter of interest (such as N content) to color parameters in calibration images, and then in using these equations to predict parameter values in new images. This allows one to convert, for example, an aerial photograph of a diseased wheat (Triticum sp.) field to a digital image in which the value of each pixel represents an estimated damage level. In a simple example use of the program, we show how percent canopy cover can be measured from color photographs. The programs, manual, and portions of the source code are in the public domain and are available at http://www.agron.iastate.edu/soilphysics/ewing_color.html.
Stability Analysis Using the SAS System
Authors: Piepho Hans‐Peter
Published: July 2010

Multienvironment trials are often analyzed to assess the yield stability of genotypes. Most of the common stability measures correspond to parameters of a mixed model with fixed genotypes and random environments. Analysis within a mixed model framework allows unbalanced data to be handled. This note shows how to fit the most common stability models using the MIXED procedure of the SAS system.
Vertical Phosphorus and Potassium Stratification in No‐Till Cotton Soils
Authors: Howard Donald D. , Essington Michael E. , Tyler Donald D.
Published: July 2010

Continuous no‐till production of cotton may result in vertical stratification of nutrients similar to that observed for band fertilizer applications. If so, special soil sampling techniques may be required to adequately address the fertility status of no‐till soils. The objective of this study was to evaluate nutrient stratification relative to the planted row and with soil depth on three soils having broadcast K at various rates applied annually for 6 years to no‐till cotton (Gossypium hirsutum L.). Rows were planted within a few centimeters of the rows from the previous year; a common practice in no‐till agriculture. The selected soils were Memphis silt loam (fine‐silty, mixed, active, thermic Typic Hapludalf), Lexington silt loam (fine‐silty, mixed, thermic Ultic Hapludalf), and Loring silt loam (fine‐silty, mixed, active, thermic Oxyaquic Fragiudalf). Potassium rates of 0, 28, 56, and 112 kg ha−1 were broadcast annually beginning in 1991. Experimental design was a split plot with five replications. Samples were collected from individual plots in the planted row (IR) and between the row (BR) to a depth of 30 cm. The soil samples were divided into 0‐ to 8‐cm, 8‐ to 15‐cm, and 15‐ to 30‐cm depths and Mehlich‐1 P and K were evaluated. Mehlich‐1 P varied with soil, sampling position, and soil depth. Differences in extractable P levels due to sampling position would not affect soil test ratings; however, additional years in no‐till production may magnify position influences and so affect P fertilizer recommendations. Mehlich‐1 K was greater for the IR sampling position of the 0‐ to 8‐cm sampling depth for the three soils. Sampling only the BR position may in some instances give a lower soil test value, resulting in higher fertilizer applications. These differences varied with soil‐applied K rates and may increase with additional time in no‐till cotton.
Soil Organic Matter and Wheat Productivity in the Semiarid Argentine Pampas
Authors: Díaz‐Zorita Martín , Buschiazzo Daniel E. , Peinemann Norman
Published: July 2010

Crop productivity under dryland conditions is largely limited by soil water availability. Soil organic matter (SOM) contents have been found to be a reliable index of crop productivity in semiarid regions because it positively affects soil water‐holding capacity. Our objectives were to explain differences in wheat (Triticum aestivum L.) yields in response to SOM levels and related properties and to quantify the contribution of a unit increment of SOM content to soil productivity during 1991, 1992, and 1994 on a total of 134 production fields in the semiarid Argentine Pampas. Wheat yields were related to both soil water retention and total organic C (TOC) contents in the top layers (0–20 cm) in years with low moisture availability (1992 [r = 0.51, P < 0.01] and 1994 [r = 0.59, P < 0.01]), and were related to both total N and available P contents in a year without water deficit stress (1991 [r = 0.58, P < 0.01]). Wheat yields over all years were linearly related to TOC (r = 0.68, P < 0.01) when these contents were <17.5 g kg−. Dependence of wheat yields on soil water retention and on TOC contents under water deficit was related to the positive effect of these soil components on plant‐available water. In the absence of water deficit (1991), nutrient availability was the limiting factor. Losses of 1 Mg SOM ha− were associated with a decrease in wheat yield of approximately 40 kg ha−. These results demonstrate the importance of using cultural practices that minimize losses of soil organic C in the semiarid Argentine Pampas.
Soil Water Dynamics after Alfalfa as Influenced by Crop Termination Technique
Authors: Bullied William J. , Entz Martin H.
Published: July 2010

Because of their deep roots and high water demand, alfalfa (Medicago sativa L.) hay crops can reduce water available to crops following in the rotation. Recharging the soil water profile after alfalfa is, therefore, a high priority in dryland cropping systems. The objective of this study was to investigate effects of alfalfa crop termination date (late June, early August, and in spring immediately before spring wheat seeding) and method (herbicides, tillage, and herbicides plus tillage) on soil water conservation, and establishment, yield, and water use efficiency (WUE) of a following spring wheat (Triticum aestivum L.) crop. Experiments were conducted over 5 site‐years in a subhumid region of western Canada. Herbicide termination resulted in greater total water recharge and a faster rate of water recharge than treatments involving tillage. Greater efficiency of soil water recharge for herbicide termination after the first hay harvest (late June) appeared to cause deep water percolation at one site. Delaying termination until after the second hay harvest (early August) did not reduce soil water availability at spring seeding of the following wheat crop, but increased reliance on overwinter soil water recharge. Delaying herbicide treatment until spring reduced water at seeding and wheat yields in some cases. Compared with treatments involving tillage, herbicide treatments resulted in higher levels of groundcover (i.e., greater soil erosion control), higher WUE, and higher grain yields. Herbicide termination after the second hay harvest produced the most favorable overall outcome; better than the traditional approach of tillage after the first hay harvest.
Growth Analysis of Five Spring and Five Winter Triticale Genotypes
Authors: Royo Conxita , Blanco Ricardo
Published: July 2010

Little is known about the pattern of growth and biomass partitioning of spring and winter triticale (×Triticosecale Wittmack), although such information can aid in interpreting the results of field experiments and is an essential step in the development of crop simulation models. This study was conducted to analyze and compare the growth of five winter and five spring triticale genotypes over two years in northeast Spain. Plants were sampled at the main stages of the Zadoks scale, and biomass, LAI and their components, and stem elongation were determined. The relationships between all the growth traits studied and accumulated growing degree‐days from sowing (GDD) were described by the same asymmetric logistic peak curve. Genotypic variability could be mainly associated with plant phenology. On average, winter triticale types needed 165 more GDD than spring types to reach maximum LAI. Also, winter triticale genotypes needed 190 more GDD to complete their main stem elongation, and 109 more GDD to reach their maximum rate of dry weight accumulation in the stems than spring genotypes did. The length of the first tiller was closer to the length of the main stem in winter types than in spring types. Both types of triticale had similar patterns of biomass accumulation. The asymmetric logistic peak curve used in this work fitted asymptotic and peak‐type relationships, and can be a useful tool for growth studies.
Chemical Dwarfing and the Response of Cool‐Season Grass Seed Crops to Spring‐Applied Nitrogen
Authors: Young William C. , Chilcote David O. , Youngberg Harold W.
Published: July 2010

Seed yield response of cool‐season grasses to spring‐applied N is usually limited because of lodging. This study investigated whether chemical dwarfing of these crops improves their seed yield response to spring‐applied N. Chewing's fescue [Festuca rubra L. subsp. fallax (Thuill.) Nyman; syn. F. rubra var. commutata Gaudin], tall fescue (Festuca arundinacea Schreb.), and orchardgrass (Dactylis glomerata L.) were established in September 1983 near Corvallis, OR. Treatments were all combinations of 90, 120, 150, 180, and 210 kg N ha−1 applied at the double‐ridge stage of development, followed by paclobutrazol [(2RS,3RS)‐l‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H1,2,4‐triazol‐1‐yl)‐pentan‐3‐ol] at 0, 0.25, 0.5, and 1 kg a.i. ha−1 applied at floret initiation stage in 1985 and 1986. Averaged across years and N rates, the 1 kg ha−1 rate reduced Chewing's fescue height by 23% and tall fescue and orchardgrass heights by 30%. In the absence of paclobutrazol, Chewing's fescue and tall fescue seed yields were the greatest at 90 kg N ha−1. Paclobutrazol did not affect seed yield response of Chewing's fescue to N rates, but tall fescue seed yield in 1986 was the greatest at 150 kg N ha−1 when only 0.25 kg a.i. paclobutrazol ha−1 was applied. Averaged across N rates, the 0.5 kg ha−1 rate increased Chewing's fescue seed yield by 32% in 1985 and 18% in 1986, and also increased tall fescue seed yield by 32% in 1985 and 23% in 1986. Orchardgrass seed yield was the greatest at 180 kg N ha−1 in both years. Paclobutrazol did not affect orchardgrass seed yield in 1985, and the 1 kg ha−1 rate decreased seed yield in 1986. We concluded that in western Oregon paclobutrazol application at floret initiation does not improve seed yield response of these crops to spring‐applied N, but it would significantly improve Chewing's fescue and tall fescue seed yield, regardless of the N rate applied. Results did not indicate any advantage for applying paclobutrazol on orchardgrass seed crop.
Switchgrass Biomass and Chemical Composition for Biofuel in Eastern Canada
Authors: Madakadze I.C. , Stewart K. , Peterson P.R. , Coulman Bruce E. , Smith Donald L.
Published: July 2010

Switchgrass (Panicum virgatum L.) is one of several warm‐season grasses that have been identified as potential biomass crops in North America. A two‐year field study was conducted, on a free‐draining sandy clay loam (St. Bernard, Typic Hapludalf), to characterize the growth and evaluate changes in biomass accumulation and composition of switchgrass at Montreal, QC. Three cultivars, Cave‐in‐Rock, Pathfinder, and Sunburst, were grown in solid stands in a randomized complete block design. Canopy height, dry matter (DM) accumulation and chemical composition were monitored biweekly throughout the growing season. Average maximum canopy heights were 192.5 cm for Cave‐in‐Rock, 169.9 for Pathfinder, and 177.8 for Sunburst. The respective end‐of‐season DM yields were 12.2, 11.5, and 10.6 Mg ha−1. Biomass production among cultivars appeared to be related to time of maturation. Nitrogen concentration of DM decreased curvilinearly from 25 g kg−1 at the beginning of the season to 5 g kg−1 DM at season's end. Both acid‐detergent fiber (ADF) and neutral‐detergent fiber (NDF) concentrations increased to a maximum early in the season, after which no changes were detected. The average maximum values of ADF and NDF were, respectively, 647.6 and 849.0 g kg−1 DM for Cave‐in‐Rock, 669.1 and 865.2 for Pathfinder, and 661.8 and 860.9 for Sunburst. Changes in canopy height, DM accumulation, and chemical composition could all be described by predictive regression equations. These results indicate that switchgrass has potential as a biomass crop in a short‐season environment.
Dryland Winter Wheat Response to Tillage and Nitrogen within an Annual Cropping System
Authors: Halvorson Ardell D. , Black Alfred L. , Krupinsky Joseph M. , Merrill Stephen D.
Published: July 2010

Winter wheat (Triticum aestivum L.) can add diversity to dryland crop rotations in the northern Great Plains, but it is susceptible to winterkill in low surface residue environments. A 12‐year study was conducted to determine the response of two winter wheat cultivars, Roughrider and Norstar, to tillage system (conventional‐till, CT; minimum‐till, MT: and no‐till, NT) and N fertilizer rate (34, 67, and 101 kg N ha−1) in a dryland spring wheat–winter wheat–sunflower (Helianthus annuus L.) rotation. Grain yields were greater with MT (1968 kg ha−1) and NT (2022 kg ha−1) than with CT (1801 kg ha−1), but tillage system effects on grain yield varied among years. Increasing N rate from 34 kg N ha−1 to 67 kg N ha−1 increased grain production from 1844 to 1953 kg ha−1, but yield response to N rate varied among years. The greatest overall grain yield (2111 kg ha−1) was obtained with NT and application of 101 kg N ha−1. Grain yields were lowest during years when plant‐available water (PAW) was <300 mm. In years with >400 mm PAW, leaf spot disease incidence was greatest, particularly at the lowest N rate with NT. Application of adequate N reduced the disease incidence in all tillage treatments. Cultivar differences were significant 3 out of 12 years, but not consistent. Winterkill was a factor for both cultivars in only 1 year in the CT and MT plots. Winter wheat performed well as a rotational crop in this cropping system when using MT and NT systems and adequate N fertility. Our long‐term results indicate that producers in the northern Great Plains can use winter wheat successfully in annual cropping systems that do not include a fallow period, particularly if NT is used with adequate N fertilization.
Statistical Tests for Hormesis and Effective Dosages in Herbicide Dose Response
Authors: Schabenberger Oliver , Tharp Brent E. , Kells James J. , Penner Donald
Published: July 2010

The log–logistic model is a popular candidate for modeling dose response in agronomy. One of its limitations is monotonicity: the response is either continuously increasing or decreasing with changes in dosage. In herbicide dose response investigations, authors have previously noted an increase in biomass or growth for subinhibitory dosages. This hormetic effect, if ignored, can lead to substantial bias in estimates of effective dosages and can distort inferences about the differential effects of experimental treatments. We present an extension of a model capable of modeling hormetic effects that allows inference about effective dosages. Furthermore, the model can be used to compare effective dosages among different treatments if hormetic effects are present for some and absent for others and provides appropriate estimates of rates of change. In a designed experiment where velvetleaf (Abutilon theophrasti Medikus) and barnyardgrass [Echinochloa crus‐galli (L.) P. Beauv.] were treated with glyphosate [isopropylamine salt of N‐(phosphonomethyl)glycine] + (NH4)2SO4 or glufosinate [2‐amino‐4‐(hydroxymethylphosphinyl)butanoic acid] + (NH4)2SO4 at various rates, hormetic effects were found for barnyardgrass treated with glyphosate but not with glufosinate. Procedures for a valid comparison of effective dosages between the two herbicides are presented. Software code to perform the analyses is given in an appendix.
Interfacing Geographic Information Systems with Agronomic Modeling: A Review
Authors: Hartkamp A. Dewi , White Jeffrey W. , Hoogenboom Gerrit
Published: July 2010

Agronomic models are traditionally used for point or site‐specific applications due to limitations in data availability as well as computer technologies. Interfacing geographic information systems (GIS) with agronomic models is attractive because it permits the simultaneous examination of spatial and temporal phenomena. The objective of this review is to examine strategies for interfacing GIS with agronomic models. It considers the diverse terminology in use, programming approaches, issues of data and scale, and existing applications. Linking is defined as merely passing input and output between a GIS and a model, combining is defined as automatic data exchange and GIS tool functions, and integrating is defined as embedding a model in a GIS or vice versa. Due to differences in research objectives, spatial and temporal scales, data sources or formats, and the natural processes being modeled, there is no universal approach for interfacing. Because of the detailed input requirements for agronomic models, expanding the models from a point‐based application to a spatial application can greatly increase the volume of input data. This review suggests that a major challenge in interfacing GIS to models lies in developing systems that handle spatial processes by implying interactions among spatial units. Moreover, extensive data requirements must be satisfied, while also ensuring data quality control.
Strip Intercropping Effects on Yield and Yield Components of Corn, Grain Sorghum, and Soybean
Authors: Lesoing Gary W. , Francis Charles A.
Published: July 2010

Strip intercropping of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] and soybean may be a viable alternative to monoculture cropping to help reduce soil erosion. Careful study of yields and yield components can add to understanding crop performance and contribute to design of more productive systems. Rainfed and irrigated experiments were conducted in eastern Nebraska from 1988 to 1990, on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll), to quantify strip‐intercropping effects on crop yields and yield components. Corn border‐row and grain sorghum border‐row yields next to soybean increased significantly compared with inside rows in the strips. Increased seed number and seed weight contributed to higher corn border‐row yields, while only seed number increased in grain sorghum border rows. Soybean border‐row yields were lower next to all corn strips and next to grain sorghum strips at the rainfed site. Soybean seed number was lower in border rows next to corn. Corn border‐row increases in seed number and seed weight indicate that competition for resources was important in both reproductive and grain‐filling periods; sorghum border‐row increases in seed number suggest competition only in the reproductive period. Higher corn density in border rows may further exploit a competitive advantage with soybean in the reproductive period, perhaps increasing system productivity. Whole‐system productivity of strip‐intercropping systems was a maximum of 4% higher than monocultures of component crops, and gross returns did not differ between the two systems. If there is need to control soil erosion, strip intercropping can be equally profitable to monoculture if production costs are similar.
Factors Related to Dryland Grain Sorghum Yield Increases: 1939 through 1997
Authors: Unger Paul W. , Baumhardt R. Louis
Published: July 2010

Grain yields of dryland (nonirrigated) grain sorghum [Sorghum bicolor (L.) Moench], a major crop in the southern Great Plains, more than tripled in studies at the USDA‐ARS Conservation and Production Research Lab., Bushland, TX, during the period from 1939 to 1997. Our objectives were to document the yield increases that occurred and to determine factors primarily responsible for the yield increases. Factors evaluated were annual precipitation, growing‐season rainfall, soil water content at planting, soil water use, growing‐season evapotranspiration, and year of record. For the report, we assembled 502 treatment‐years of grain yield data from 37 studies. For the 1939–1997 period, grain yields increased about 50 kg ha−1 annually. Yields increased 139% during the 1956–1997 period, with 46 of those percentage units resulting from use of improved hybrids, based on results of a uniformly managed 40‐year study. The remaining 93 percentage units for that period were attributed to other factors, primarily to soil water at planting. Increases in soil water at planting resulted from changes in management practices with time, mainly the adoption of improved crop residue management practices after about 1970.
Soil Nitrogen Dynamics and Maize Production in Municipal Solid Waste Amended Soil
Authors: Eriksen George N. , Coale Frank J. , Bollero German A.
Published: July 2010

Municipal solid waste compost (MSWC) can enhance soil organic matter and crop nutrient supply. High C:N ratio composts can temporarily deplete plant‐available soil N reserves, requiring supplemental N fertilization to ensure optimum crop growth. The objective of our research was to measure seasonal soil NO3–N dynamics to serve as an indication of N mineralization, immobilization, and leaching as affected by MSWC and N fertilizer rates. The MSWC (C:N 40:1) was applied in one year only to a Galestown sand (sandy, siliceous, mesic Psammentic Hapludults) at rates of 0, 63, 126, and 189 Mg ha−1 Maize (Zea mays L.) was planted and N fertilizer rates of 0, 168, 336, 504, and 672 kg ha−1 were applied as split‐plot treatments. First‐year maize total dry matter production plateaued at the 250 kg ha−1 N rate, averaged across MSWC rates. Soil NO3–N decreased inversely proportional to MSWC rates, due to MSWC immobilization of soil and fertilizer N. Cereal rye (Secale cereale L.) winter cover crop total dry matter yield and total crop N increased linearly with increasing MSWC rates. Second‐year maize total dry matter, total plant N, maize grain yield, and grain N increased linearly with increased MSWC rates applied the first year. During the second growing season, there was an increasing supply of plant‐available N, due to mineralization of organic N in the MSWC with increasing MSWC rate; however, the supply of mineralized N was inadequate to meet crop growth requirements for maximum maize yield.
Plant Density and Hybrid Influence on Corn Forage Yield and Quality
Authors: Cusicanqui Jorge A. , Lauer Joseph G.
Published: July 2010

Corn (Zea mays L.) hybrid selection and plant density are important management considerations for successful forage production in dairy and livestock operations. The objectives of this study were (i) to determine the effect of plant density on high‐ and low‐quality corn hybrids and (ii) to describe the economic trade‐off between plant density and forage yield and quality. Two adapted hybrids selected for high and low quality characteristics were grown in the field at five plant densities ranging from 44 500 to 104 500 plants ha−1 at six locations in Wisconsin during 1994, 1995, and 1996. Forage quality response among hybrids was similar across the range of plant densities evaluated. As plant density increased, dry matter yield increased 1.7 to 4.1 Mg ha−1, depending on location. Maximum dry matter yields were observed at 97 300 to 102 200 harvested plants ha−1. In vitro true digestibility decreased 16 to 23 g kg−1 as plant density increased. Crude protein decreased 6 to 8 g kg−1 as plant density increased. Neutral‐detergent fiber increased 20 to 35 g kg−1, and acid‐detergent fiber increased 19 to 29 g kg−1 with increasing plant density. A trade‐off exists between yield and quality for corn forage. Milk Mg−1 decreased 98 to 143 kg milk Mg−1 with increasing plant densities, but milk ha−1 increased 926 to 2176 kg milk ha−1 until about 75 000 to 85 000 harvested plants ha−1, and did not change with higher plant densities.
Guidelines for Comparisons among Different Maize Maturity Rating Systems
Authors: Dwyer Lianne M. , Stewart Douglas W. , Carrigan L. , Ma B. L. , Neave P. , Balchin D.
Published: July 2010

Several systems are extensively used to rate maize (Zea mays L.) maturity in North America, including growing degree days, crop heat units, and Minnesota relative maturity rating days. Correspondence between the different systems varies with the temperature range of the environment, because of different bases of calculation and unit size. However, general guidelines for conversion from one system to another would aid communication among researchers, producers, distributors, and extension personnel, particularly where regional preference for one system exists, but information developed in another region is shared. Simple regression equations were developed from a data set with 4 years, 28 hybrids, and 19 locations (between 39° and 48° N lat). Coefficients of determination were ≥0.91, indicating that these equations could be used as a general guideline to compare maturity ratings developed using the different systems.
Legume Decomposition and Nitrogen Release When Applied as Green Manures to Tropical Vegetable Production Systems
Authors: Th o ¨ nnissen Carmen , Midmore David J. , Ladha Jagdish K. , Olk Daniel C. , Schmidhalter Urs
Published: July 2010

For legume green manures (GM) to be effective, environmentally sound N sources for horticultural crops in the tropics, their N release must be in synchrony with crop N demand. Decomposition and N release of surface applied (mulch) or incorporated soybean [Glycine max (L.) Merr.] and indigofera (Indigofera tinctoria L.) GM were studied in six field studies conducted at three locations in Taiwan and the Philippines between 1993 and 1995. Litter bags and inorganic N soil samplings were used in order to understand tomato (Lycopersicon esculentum Mill.) crop responses to GM N. Resulting soil N contents were compared with a control (no GM, no fertilizer). The N content of 60 to 74 d soybean GM varied between 110 and 140 kg N ha−1 and that of indigofera between 5 and 40 kg N ha−1. Nitrogen‐15‐labeled soybean GM was traced in the soil and in organic matter fractions (humic acids, calcium humates, humins) in one of the field studies. Soybean and indigofera decomposed rapidly, losing 30 to 70% of their biomass within 5 wk after application, depending on GM placement, season (wet vs. dry), and location. Soil nitrate contents increased corresponding to GM N release at all locations and seasons, with a maximum increase of 80 to 100 kg NO3–N ha−1 with incorporated soybean. The peak N release occurred 2 to 6 wk after GM application in two of the three locations, and 5 to 8 wk in the third location. The apparent decline of GM N release at all locations and seasons 8 wk after application was only partly caused by tomato N uptake. At tomato harvest, 30 to 60% of the GM 15N was found in the soil, and was found mostly in humins. Comparable N release dynamics across seasons and locations suggest a possible N fertilizer substitution by incorporated soybean GM for basal N application and first side dressing to tomato. With respect to season and location, GM N should be supplemented with N fertilizer starting after 8 wk to ensure optimal tomato yields.
Comparing Simulated and Measured Values Using Mean Squared Deviation and its Components
Authors: Kobayashi Kazuhiko , Salam Moin Us
Published: July 2010

When output (x) of a mechanistic model is compared with measurement (y), it is common practice to calculate the correlation coefficient between x and y, and to regress y on x. There are, however, problems in this approach. The assumption of the regression, that y is linearly related to x, is not guaranteed and is unnecessary for the x–y comparison. The correlation and regression coefficients are not explicitly related to other commonly used statistics [e.g., root mean squared deviation (RMSD)]. We present an approach based on the mean squared deviation (MSD = RMSD2) and show that it is better suited to the x–y comparison than regression. Mean squared deviation is the sum of three components: squared bias (SB), squared difference between standard deviations (SDSD), and lack of correlation weighted by the standard deviations (LCS). To show examples, the MSD‐based analysis was applied to simulation vs. measurement comparisons in literature, and the results were compared with those from regression analysis. The analysis of MSD clearly identified the simulation vs. measurement contrasts with larger deviation than others; the correlation–regression approach tended to focus on the contrasts with lower correlation and regression line far from the equality line. It was also shown that results of the MSD‐based analysis were easier to interpret than those of regression analysis. This is because the three MSD components are simply additive and all constituents of the MSD components are explicit. This approach will be useful to quantify the deviation of calculated values obtained with this model from measurements.
Site‐Specific Analysis of a Droughted Corn Crop: I. Growth and Grain Yield
Authors: Sadler E. John , Bauer Philip J. , Busscher Warren J.
Published: July 2010

Soil in the southeastern USA Coastal Plain exhibits marked variation, especially near shallow depressions called Carolina Bays. This variation causes correspondingly severe variation in yield, particularly for corn (Zea mays L.) during drought. Though important to precision farming, these features often are overlooked in 1:20000 scale county soil surveys. They are visible in 1:1200 scale soil surveys, but the ability to explain yield variation using soil map units at this scale must be unequivocally demonstrated before committing resources to such a detailed survey. Our objectives were (i) to compare paired samples of four soil map units to determine if grain yield variation were sufficiently explained to be of practical value, and (ii) to extend this evaluation to include data with greater spatial coverage. Corn grain yields were measured at 209 sites in an 8‐ha field, including two Carolina Bays near Florence, SC. Site‐specific effects of soil variation on crop phenology, biomass, and yield components were measured at 11 sites during a drought. Variations in yield components were large and sometimes compensatory (e.g., kernel number and mass), with distinctly different routes to sometimes similar final grain yields. Multiple sites within map units were frequently different at α = 0.05. Analysis of variance for grain yield on soil map unit was statistically significant (P < 0.001) but of limited explanatory value (r2 = 0.16). We conclude that to create soil management zones for precision farming, one must augment even detailed soil map units with additional spatial data, such as yield maps.
Effect of Soil Phosphorus on Leaf Development and Senescence Dynamics of Field‐Grown Maize
Authors: Colomb Bruno , Kiniry Jim R. , Debaeke Philippe
Published: July 2010

Phosphorus deficiency generally decreases plant biomass accumulation by limiting interception of photosynthetically active radiation (PAR) rather than reducing efficiency of conversion of PAR into dry matter. To document the role of P availability in leaf growth and senescence dynamics in maize (Zea mays L.), a 3‐yr field experiment was conducted in southern France with very low, moderate, high, or very high soil test P levels. Leaf appearance rate, individual leaf area, and green fraction changes were recorded at weekly intervals. Rates and duration of expansion and senescence processes were derived independently from fitted logistic functions. Phosphorus deficiency slowed the rate of leaf appearance and reduced the final area of leaves located below the main ear by 18 to 27%, depending on year. The reduction in leaf expansion rates accounted for most of the area reduction over leaf position and years. Senescence rates of the lower leaves were reduced by 29%. The expansion and senescence dynamics of upper leaves were little affected by soil P level. The whole plant peak green leaf area was lower under P‐stressed conditions (16%), and its date of occurrence was significantly delayed (6%). Plant senescence rate was reduced by 15 to 33% during most of the grain filling period. Leaf area duration from emergence to complete senescence was reduced by 13.5%. The early effects of P deficiency on leaf dynamics accounted for most of the 7 to 10% reduction in the amount of absorbed PAR, observed as soon as canopy development allowed maximum light interception.
Tillage × Rotation × Management Interactions in Corn
Authors: Katsvairo Tawainga W. , Cox William J.
Published: July 2010

Although corn (Zea mays L.) yields following soybean [Glycine max (L.) Merr.] or wheat (Triticum aestivum L.) exceed yields of continuous corn, continuous corn is common in the northeastern USA because of demand for corn by the dairy industry. We evaluated corn under different tillage (moldboard plow, chisel, and ridge), rotation (continuous corn, soybean–corn, soybean–corn–corn, and soybean–wheat/red clover (Trifolium pratense L.)–corn), and management systems (high and low chemical input) for 6 yr to determine optimum cropping systems for corn. In moldboard plow, corn in soybean–wheat/red clover–corn (9.2 Mg ha−1) and soybean–corn (8.5 Mg ha−1) rotations under low chemical yielded greater than continuous corn under high chemical management (7.9 Mg ha−1). In chisel tillage, corn in the soybean–corn rotation yielded greater under high chemical (8.9 Mg ha−1) and similarly under low chemical (7.9 Mg ha−1) compared with continuous corn under high chemical management (7.6 Mg ha−1). In ridge tillage, corn in soybean–corn or first‐year corn in soybean–corn–corn rotations yielded greater under high chemical (8.1 Mg ha−1) but less under low chemical (6.3 and 6.8 Mg ha−1, respectively) compared with continuous corn under high chemical management (7.5 Mg ha−1). Growers under similar environmental conditions to this study can increase corn yields while reducing inputs by adopting soybean–wheat/red clover–corn and soybean–corn rotations in moldboard plow or a soybean–corn rotation in chisel tillage. In ridge tillage, growers could adopt soybean–corn or soybean–corn–corn rotations, which would increase corn yields but not reduce inputs when compared with continuous corn.
Diseases Caused by Dematiaceous Fungal Pathogens as Potential Limiting Factors for Production of Bermudagrass on Swine Effluent Application Sites
Authors: Pratt Robert G.
Published: July 2010

Plant diseases that reduce the survival and productivity of forage crops on animal waste disposal sites may limit removal of waste‐derived nutrients in harvested hay. However, no studies have documented the occurrence and importance of plant diseases on waste disposal sites in the southeastern USA. During 1998, symptoms of leaf, stem, crown, and root necrosis were observed in common bermudagrass [Cynodon dactylon (L.) Pers.] on three swine waste disposal sites in Mississippi. Species of Exserohilum, Bipolaris, and Curvularia grew from 82 to 100% of leaf and stem tissues from symptomatic plants, and six species were identified among 266 isolates. E. rostratum (Drechs.) Leonard & Suggs and B. spicifera (Bainier) Subramanian were most frequent in samples from a severely diseased stand, and C. lunata (Wakk.) Boedijn and C. geniculata (Tracy & Earle) Boedijn were most frequent from moderately and slightly diseased stands. In inoculation experiments, E. rostratum was most virulent and caused extensive necrosis of bermudagrass leaves; B. stenospila (Drechs.) Shoemaker, B. cynodontis (Marignoni) Shoemaker, and B. spicifera were intermediate in virulence; and C. lunata and C. geniculata were least virulent. When samples of healthy and diseased bermudagrass from a severely diseased site were compared for forage production over three harvests in the greenhouse, mean dry matter yields of diseased grass were 37 to 52% of healthy yields. Results indicate that dematiaceous fungal diseases may cause stand decline and yield reduction of bermudagrass on swine effluent application sites, and that E. rostratum and Bipolaris spp. are the most damaging pathogens encountered to date.
No‐Tillage Soybean Response to Banded and Broadcast and Direct and Residual Fertilizer Phosphorus and Potassium Applications
Authors: Buah Samuel S.J. , Polito Thomas A. , Killorn Randy
Published: July 2010

Improved P and K management systems for no‐tillage soybean [Glycine max (L.) Merr.] may be needed to increase yield and profits. This study evaluated the response of soybean to fertilizer P or K rates and placement as well as residual and direct fertilization from 1995 through 1996. Two K and two P experiments were established on farmers’ fields with 10‐yr histories of no tillage. An additional P experiment was conducted on one of Iowa State University's research farms. Treatments on farmers’ fields included two rates of P (0 and 19.5 kg P ha−1) or K (0 and 51 kg K ha−1), placement of fertilizer (surface broadcast or a subsurface band 5 cm beside and 5 cm below the seed) and time of fertilizer application. Treatments on the research farm were similar, except the P fertilizer rates applied were 0, 19, 39, and 78 kg ha−1. Leaf P and K concentrations and grain yields were measured. Soil test P and K levels at the 0‐ to 15‐cm depths ranged from low to very high across sites at the beginning of the experiment. Placement effects were variable for leaf P or K concentrations. Grain yields for broadcast P and K were as good as or better than the banded applications. However, there may be an advantage to applying P directly to the soybean crop, at least when soil test levels are optimum or lower.
Simulation of Maize Yield under Water Stress with the EPICphase and CROPWAT Models
Authors: Cavero Jose , Farre Inma , Debaeke Philippe , Faci Jose M.
Published: July 2010

Models that simulate the effects of water stress on crop yield can be valuable tools in irrigation. We evaluated the crop growth simulation model EPICphase and the model CROPWAT on their ability to simulate maize (Zea mays L.) grain yield reduction caused by water stress under semiarid conditions. The simulation of evapotranspiration (ET), harvest index (HI), leaf area index (LAI), and final biomass was also evaluated. Data from three field experiments were used to test the models. In one sprinkler‐irrigated experiment, different water amounts (0–592 mm) were applied, producing a continuous water deficit. The other two experiments were flood‐irrigated and water stress was imposed at given development stages of maize. EPICphase simulated the ET with a root mean square error (RMSE) of 40 mm. The regression of the EPICphase simulated vs. measured values of HI and yield had intercepts that were not significantly different from 0 and slopes not different from 1. EPICphase overestimated the biomass in the more water‐stressed treatments (intercept of simulated vs. measured values = 5.25 t ha−1) due to overestimation of LAI. Modifications of EPICphase relative to the effect of water stress on LAI growth and on the light extinction coefficient improved the simulations of LAI, biomass, HI, and yield. CROPWAT calculated maize grain yield with a RMSE of 14% but overestimated ET in the flood‐irrigated treatments . Better simulation of ET by EPICphase makes this model more consistent for calculating yield reduction due to water stress.
Assessing Spatial Variability in an Agricultural Experiment Station Field: Opportunities Arising from Spatial Dependence
Authors: Cassel D.K. , Wendroth O. , Nielsen D.R.
Published: July 2010

Spatio‐temporal field soil and crop processes are important for site‐specific farming. The objectives of this study were to spatially evaluate selected soil physical and chemical properties and their relationship to wheat (Triticum aestivum L.) yield, and to discuss stochastic approaches to help identify processes underlying yield variability in heterogeneous field sites. Modified grid sampling included 330 sites including a primary transect. Soil properties measured for the Ap, E if present, and upper B horizons at each site included pH, P, Zn, Cu, exchangeable cations, percentage base saturation, cation exchange capacity, bulk density, soil water contents at −10, −33, and −1500 kPa, texture, and humic matter content. Wheat grain and straw were hand‐harvested on 1‐ by 2‐m plots centered on each site. Soil water content on the primary transect was determined by neutron attenuation on nine dates. Field and primary transect means and semivariograms for a given soil or plant parameter were similar. The range of spatial dependence or autocorrelation of soil parameters ranged from 10 m for Ap horizon depth to 100 m for −1500 kPa water content of the Ap. Base saturation and available water storage capacity were cross‐correlated with grain yield to a distance of ±15 and 12.5 m, respectively. State‐space analysis was used to develop a grain yield model using these two variables. Spearman rank correlation of the soil water content data suggests that the temporal stability of soil water storage is less for shallow than for deeper soil layers.
Effects of Light, Growth Media, and Seedling Orientation on Bioassays of Alfalfa Autotoxicity
Authors: Chon Sang‐Uk , Coutts John H. , Nelson C. Jerry
Published: July 2010

Most assessments of allelopathy involve bioassays. Our objective was to improve the sensitivity of an alfalfa (Medicago sativa L.) seedling bioassay for evaluating genetic tolerance to autotoxic leaf extracts. In a petri dish assay on imbibed seed, light inhibited hypocotyl elongation of controls and increased root elongation. Root growth was sensitive to the autotoxin in both light and darkness. An agar medium gave better root growth of controls and lower standard errors than did filter paper when petri dishes were placed on edge to encourage downward root growth or were placed flat where roots grew laterally. Hypocotyl growth was not very sensitive to the autotoxic chemical(s) on either agar or paper medium when the plate was flat, because the hypocotyl arched upward to escape contact with the extract. Hypocotyl growth was sensitive in a rolled paper towel treatment held vertically because the hypocotyl remained in continuous contact with the extract. On agar plates placed flat, 50% inhibition of root length occurred at an extract concentration that was about 8% of that needed for 50% inhibition of germination at 36 and 48 h. Root growth was stimulated up to 15% above controls at very low concentrations of leaf extract. Root length at 120 h was the best indicator of autotoxic effects of alfalfa leaf extracts. We evaluated 17 germplasms and three cultivars of alfalfa for root growth response to the autotoxic chemical and found a twofold range (P < 0.05) in tolerance.
Rhizobial Inoculation Influences Seedling Vigor and Yield of Rice
Authors: Biswas Jatish C. , Ladha Jagdish K. , Dazzo Frank B. , Yanni Youssef G. , Rolfe Barry G.
Published: July 2010

Rice (Oryza sativa L.) is one of the world's most important crops. The present investigation was designed to assess the range of growth‐promoting activities of various diazotrophic bacteria on rice seedling vigor, its carryover effect on straw and grain yield, and the persistence of an inoculant strain on rice roots under greenhouse conditions. Growth responses to inoculation exhibited bacterial strain–rice variety specificity that were either stimulatory or inhibitory. Growth responses included changes in rates of seedling emergence, radical elongation, height and dry matter, plumule length, cumulative leaf and root areas, and grain and straw yields. Most notable were the inoculation responses to Rhizobium leguminosarum bv. trifolii E11 and Rhizobium sp. IRBG74, which stimulated early rice growth resulting in a carryover effect of significantly increased grain and straw yields at maturity, even though their culturable populations on roots diminished to below detectable values at 60 d after planting. The test strains were positive for indole‐3‐acetic acid production in vitro, but only some reduced acetylene to ethylene in association with rice under laboratory growth conditions. These studies indicate that certain strains of nonphotosynthetic diazotrophs, including rhizobia, can promote growth and vigor of rice seedlings, and this benefit of early seedling development can carryover to significantly increased grain yield at maturity.
Physiological Maturity in Wheat Based on Kernel Water and Dry Matter
Authors: Calderini Daniel F. , Abeledo Leonor G. , Slafer Gustavo A.
Published: July 2010

Estimation of the time of physiological maturity could be beneficial to avoid yield penalties due to lodging, sprouting, hail, and other harvest risks. The aim of our study was to evaluate a simple empirical relationship (model) to determine physiological maturity by simultaneously analyzing the water and dry matter dynamics of wheat kernels. An experiment was conducted in which two cultivars with different kernel mass potential were sown on four dates. Fresh and dry kernel mass from different positions in the spike were measured twice weekly. To validate the regression model, measured and calculated data from different cultivars, growing seasons, and kernel positions were compared. A negative linear relationship between kernel dry matter (relative to final kernel mass) and kernel water concentration was determined. This showed that in wheat, physiological maturity is reached at 37% of kernel water concentration. Validation of the regression model was done using data from field experiments in Argentina and Mexico, and from controlled‐conditions experiments reported in the literature. The regression model successfully simulated results from field experiments (.) In addition, data from controlled‐conditions experiments showed the same negative linear relationship between relative kernel dry matter and kernel water concentration (), and the model achieved a good fit for measured data (). This regression model is proposed for use by farmers and crop managers, who can simply measure grain humidity with grain moisture meters.