Agronomy Journal

Published by American Society of Agronomy
Online ISSN: 1435-0645
Publications
Article
High-pressure sodium (HPS) lamps are popular for plant lighting because of their high energy conversion efficiencies. Yet their spectrum has very little blue light (BL), which may cause undesirable morphological responses. To study this, McCall' soybean [Glycine max (L.) Merr.] plants were grown for 28 d in growth chambers using HPS lamps, with or without supplemental light from blue phosphor fluorescent lamps. Total photosynthetic photon flux (PPF) levels (including blue fluorescent) were kept near 300 or 500 micromoles m-2 s-1. Blue fluorescent levels ranged from 7 to 20 micromoles m-2 s-1, providing from 6 to 18 micromoles m-2 s-1 of supplemental BL (400-500 nm). Stem and internode lengths were longest under 300 micromoles m-2 s-1 HPS lighting and became progressively shorter with increasing supplemental BL until a total of approximately 30 micromoles m-2 s-1 of BL (from HPS and BL supplement) was present in the spectrum. Beyond this, extra BL had no effect. Two other lamps rich in BL, metal halide (Optimarc) and fluorescent (Vita-Lite), also produced plants with short stems, as did HPS lighting maintained at 500 micromoles m-2 s-1. Results suggest that use of high-pressure sodium or other blue-deficient sources for lighting at low to moderate photosynthetic photon flux levels may cause abnormal stem elongation, but this can be prevented by adding a small amount of supplemental blue light.
 
Article
Portable closed chambers provide a valuable tool for measuring crop photosynthesis and evapotranspiration. Typically, the rates of change of CO2 and water vapor concentration are assumed to be constant in the short time required to make the closed-chamber measurement, and a linear regression model is used to estimate the CO2 and H2O fluxes. However, due to the physical and physiological effects the measurement system has on the measured process, assuming a constant rate and using a linear model may underestimate the flux. Our objective was to provide a model that estimates the CO2 and H20 exchange rates at the time of chamber closure. We compared the linear regression model with a quadratic regression model using field measurements from two studies. Generally, 60 to 100% of all chamber measurement data sets were significantly nonlinear, causing the quadratic model to yield fluxes 10 to 40% greater than those calculated with the linear regression model. The frequency and degree of nonlinearity were related to the measured rate and chamber volume. Closed-chamber data should be tested for nonlinearity and an appropriate model used to calculate flux. The quadratic model provides users of well-mixed closed chambers an alternative to a simple linear model for data sets with significant nonlinearity.
 
Matric potential (P ) as a function of water content () for  
Percentage of wheat biomass partitioned to roots and tillers  
Water potential gradients from substrate or hydroponic nutrient solution to roots and then leaves measured in the light (left ) and water status of flag leaves in the light and dark (right ). Dark measurements were made 4 h after lights had been turned off. Closed symbols represent hydroponic culture; open symbols represent zeoponic substrate with microporous tube irrigation culture (ZPT). Symbols represent means; error bars indicate SD, where larger than symbol size. Substrate and root water potentials, and nutrient solution osmotic potential, n 3; leaf water potential, n 6.  
Water use of 'USU-Apogee' wheat grown in zeoponic  
Article
Hydroponic culture has traditionally been used for controlled environment life support systems (CELSS) because the optimal environment for roots supports high growth rates. Recent developments in zeoponic substrate and microporous tube irrigation (ZPT) also offer high control of the root environment. This study compared the effect of differences in water and nutrient status of ZPT or hydroponic culture on growth and yield of wheat (Triticum aestivum L. cv. USU-Apogee). In a side-by-side test in a controlled environment, wheat was grown in ZPT and recirculating hydroponics to maturity. Water use by plants grown in both culture systems peaked at 15 to 20 L m-2 d-1 up to Day 40, after which it declined more rapidly for plants grown in ZPT culture due to earlier senescence of leaves. No consistent differences in water status were noted between plants grown in the two culture systems. Although yield was similar, harvest index was 28% lower for plants grown in ZPT than in hydroponic culture. Sterile green tillers made up 12 and 0% of the biomass of plants grown in ZPT and hydroponic culture, respectively. Differences in biomass partitioning were attributed primarily to NH4-N nutrition of plants grown in ZPT compared with NO3-N in hydroponic nutrient solution. It is probable that NH4-N-induced Ca deficiency produced excess tillering and lower harvest index for plants grown in ZPT culture. These results suggest that further refinements in zeoponic substrate would make ZPT culture a viable alternative for achieving high productivity in a CELSS.
 
Article
The relationships between crop canopy variables such as leaf area index (LAI) and their multispectral reflectance properties were investigated along with the potential for estimating canopy variables from remotely sensed reflectance measurements. Reflectance spectra over the 0.4 to 2.5 micron wavelength range were acquired during each of the major development stages of spring wheat canopies at Williston, North Dakota, during three seasons. Treatments included planting date, N fertilization, cultivar, and soil moisture. Agronomic measurements included development stage, biomass, LAI, and percent soil cover. High correlations were found between reflectance and percent cover, LAI, and biomass. A near infrared wavelength band, 0.76 to 0.90 microns, was most important in explaining variation in LAI and percent cover, while a middle infrared band, 2.08 to 2.35 microns, explained the most variation in biomass and plant water content. Transformations, including the near infrared/red reflectance ratio and greenness index, were also highly correlated to canopy variables. The relationship of canopy variables to reflectance decreased as the crop began to ripen. the canopy variables could be accurately predicted using measurements from three to five wavelength bands. The wavelength bands proposed for the thematic mapper sensor were more strongly related to the canopy variables than the LANDSAT MSS bands.
 
Article
Data were acquired on canopies of mature corn planted in 76 cm rows, mature soybeans planted in 96 cm rows with 71 percent soil cover, and mature soybeans planed in 76 cm rows with 100 percent soil cover. A LANDSAT band radiometer with a 15 degree field of view was used at ten altitudes ranging from 0.2 m to 10 m above the canopy. At each altitude, measurements were taken at 15 cm intervals also a 2.0 m transect perpendicular to the crop row direction. Reflectance data were plotted as a function of altitude and horizontal position to verify that the variance of measurements at low altitudes was attributable to row effects which disappear at higher altitudes where the sensor integrate across several rows. The coefficient of variation of reflectance decreased exponentially as the sensor was elevated. Systematic sampling (at odd multiples of 0.5 times the row spacing interval) required fewer measurements than simple random sampling over row crop canopies.
 
Article
Increased knowledge about the spatial distribution of cotton (Gossypium hirsutum L.) yield in the Khorezm region in Uzbekistan supports the optimal allocation of resources. This research estimated the spatial distribution of cotton yields in Khorezm by integrating remote sensing, field data, and modeling. The agro-meteorological model used was based on Monteith’s biomass production model with multitemporal MODIS (Moderate Resolution Imaging Spectroradiometer)- derived parameters from 2002 as primary inputs. The photosynthetically active radiation (PAR) and environmental stress scalars on crop development were estimated with meteorological information. Using high-spatial-resolution Landsat 7 ETM+ images, the cotton area was extracted and the cotton fraction determined within the coarse spatial resolution MODIS pixels. The spatial resolution of the MODISFPARdata was improved by using an empirical relationship to the higher-resolution MODIS NDVI (Normalized Difference Vegetation Index) data. The estimated raw cotton yield ranged from 1.09 to 3.76 Mg ha<sup>-1</sup>. The modeling revealed a spatial trend of higher yields in upstream areas and in locations closer to the irrigation channels and lower yields in downstream areas and at sites more distant to the channels. The validated yield estimations showed a 10% deviation from official governmental statistics. The established agro-meteorological model based on freely available MODIS data and a minimum of field data input is a promising technique for economic and operational lateseason estimation of spatially distributed cotton yield over large regions on which management adjustments could be made.
 
Article
Using stochastic frontier analysis, efficiency of production of wheat in Western Australia was studied. The production function model used was a relatively simple input model, consisting of wheat yield, effective rainfall, fertilizer application rates and year of study. Inefficiency was captured in a second model that incorporated machinery capital investment, opening equity level, and year of study. Data covered the production years 2004 through to 2007. The results demonstrated that inefficiency was present in wheat production in Western Australia and that inefficiency increased over the period from 18% in 2004 to 29% in 2007. Higher machinery investment per hectare and opening equity levels reduced inefficiency, due to producers having sufficient capacity, mechanical or financial, to adapt to variability within the production season. The results demonstrated the stochastic nature of efficiency and that for some firms improving efficiency may not be possible or feasible due to limitations within the firm. This also holds for firms that are relatively efficient in some years and that the reasons for the inefficiency are not necessarily production related, hence, programs targeted to improve efficiency may not be very successful. On the other hand firms that are consistently inefficient provide an ideal target audience for programs to improve efficiency. However, these programs must be conditioned on adequately identifying the source(s) of inefficiency and the producer having access to resources to increase efficiency. Similar analyses could be undertaken in different crops or different geographic locations, to identify if and why inefficiencies are present in other production systems.
 
Article
Do extended crop rotations that include forages improve soil quality and are they profitable? Our objectives were to determine (i) how crop rotation affected soil quality indicators, (ii) if those indicator changes were reflected in soil quality index (SQI) ratings when scored and combined using the Soil Management Assessment Framework, and (iii) how SQI values compared with profitability. Soil samples were collected from three long-term studies in Iowa and one in Wisconsin. Bulk density (BD), soil pH, water-stable macroaggregation, total organic C, total N, microbial biomass C, extractable P and K, and penetration resistance were measured. The indicator data were scored using nonlinear curves reflecting performance of critical soil functions (e.g., nutrient cycling, water partitioning and storage, and plant root growth). Profit was calculated by subtracting costs of production from potential income based on actual crop yields and the 20-yr average nongovernment-supported commodity prices. Extended rotations had a positive effect on soil quality indicators. Total organic C was the most sensitive indicator, showing significant measured and scored differences at all locations, while BD showed significant differences at only one location (Kanawha). The lowest SQI values and 20-yr average profit were associated with continuous corn, while extended rotations that included at least 3 yr of forage crops had the highest SQI values. We suggest that future conservation policies and programs reward more diverse and extended crop rotations, as is being done through the Conservation Security Program.
 
Article
The effects of available soil moisture, planting date, nitrogen fertilization, and cultivar on reflectance of spring wheat (Triticum aestivum L.) canopies were investigated. Spectral measurements were acquired on eight dates throughout the growing season, along with measurements of crop maturity stage, leaf area index, biomass, plant height, percent soil cover, and soil moisture. Planting date and available soil moisture were the primary agronomic factors which affected reflectance of spring wheat canopies from tillering to maturity. Comparisons of treatments indicated that during the seedling and tillering stages planting date was associated with 36 percent and 85 percent of variation in red and near infrared reflectances, respectively. As the wheat headed and matured, less of the variation in reflectance was associated with planting date and more with available soil moisture. By mid July, soil moisture accounted for 73 percent and 69 percent of the variation in reflectance in red and near infrared bands, respectively. Differences in spectral reflectance among treatments were attributed to changes in leaf area index, biomass, and percent soil cover. Cultivar and N fertilization rate were associated with very little of the variation in the reflectance of these canopies.
 
Article
Reflectance factor data were acquired with a Landsat band radiometer throughout two growing seasons for corn (Zea mays L.) canopies differing in planting dates, populations, and soil types. Agronomic data collected included leaf area index (LAI), biomass, development stage, and final grain yields. The spectral variable, greenness, was associated with 78 percent of the variation in LAI over all treatments. Single observations of LAI or greenness have limited value in predicting corn yields. The proportions of solar radiation intercepted (SRI) by these canopies were estimated using either measured LAI or greenness. Both SRI estimates, when accumulated over the growing season, accounted for approximately 65 percent of the variation in yields. Models which simulated the daily effects of weather and intercepted solar radiation on growth had the highest correlations to grain yields. This concept of estimating intercepted solar radiation using spectral data represents a viable approach for merging spectral and meteorological data for crop yield models.
 
Article
Confirming the precision agriculture hypothesis for variable rate nitrogen applications (VRA) has proven challenging. To confront this challenge, researchers have begun to use increasingly sophisticated statistical models to estimate and compare site-specific crop response functions. While progress has been made, we believe it has been hampered by the lack of a clear conceptual framework to guide and motivate the development of appropriate models and methods. The purpose of this paper was to provide such a framework, while demonstrating its utility. The framework was used to develop a heteroscedastic, fixed and random effects, geostatistical model to test the potential for VRA to increase nitrogen returns. The model was implemented with data collected in 1995 from two corn nitrogen response experiments conducted in South Central Minnesota. Results of the analysis indicate there is significant potential to increase nitrogen returns using VRA. At one location, there was greater than a 95 percent chance that VRA would have increased profitability if the cost of implementing VRA was less than 14.5 $ ha-1. At the other location, if implementation costs were less than 48.3 $ ha-1, there was greater than a 95 percent chance for increased profitability through VRA.
 
Regressions and standard errors of the estimate (Syx) for models of area per leaf of corn as functions of the product of leaf length and width in 1982 (n=496).
Regressions and standard errors of the estimates (Syx) for models of leaf area per plant as functions of the dry weight of leaves per plant in 1982 (n=40).
Descriptive statistics for 40 corn plants sampled at milk- stage (R3) development in 1982.
Total relative costs for measuring leaf area of corn plants. Equations 2, 3, 4, and 5 are used to compute LAI for methods I, II, III, and IV, respectively.
Article
The magnitude of plant-to-plant variability of leaf area of corn plants selected from uniform plots was examined and four representative methods for measuring leaf area index (LAI) were evaluated. The number of plants required and the relative costs for each sampling method were calculated to detect 10, 20, and 50% differences in LAI using 0.05 and 0.01 tests of significance and a 90% probability of success (beta = 0.1). The natural variability of leaf area per corn plant was nearly 10%. Additional variability or experimental error may be introduced by the measurement technique employed and by nonuniformity within the plot. Direct measurement of leaf area with an electronic area meter had the lowest CV, required that the fewest plants be sampled, but required approximately the same amount of time as the leaf area/weight ratio method to detect comparable differences. Indirect methods based on measurements of length and width of leaves required more plants but less total time than the direct method. Unless the coefficients for converting length and width to area are verified frequently, the indirect methods may be biased. When true differences in LAI among treatments exceed 50% of mean, all four methods are equal. The method of choice depends on the resources available, the differences to be detected, and what additional information, such as leaf weight or stalk weight, is also desired.
 
Article
Measurements of spectral reflectance characteristics during a growing season of leaves from six crops are reported. These crops include soybeans, wheat, oats, sorghum, corn, and sudangrass. The characteristics measured are related to changes in leaf structure and water content.
 
Article
Spectroradiometric reflectance measurements were made on Target and Torch plants (four and five leaves, respectively) that were growing in 0.09 m2 soil-containing flats. Torch's spectrophotometric single leaf reflectance was consistently lower than Target's at the 650-nm chlorophyll absorption band because Torch's chlorophyll concentration was larger than Target's, which caused more red light absorption. Spectroradiometric measurements indicate that: wet soil strongly absorbs visible light (500 to 700 nm) so that Target's soil-containing flat with 60% plant cover has less reflectance than Torch's soil-containing flat with 75% plant cover; Torch (most foiliage) has higher near-infrared (750 to 1,350 nm) reflectance than Target (least foliage); and the 2,200-nm wavelength is a candidate band to distinguish Target from Torch. The difference in chlorophyll concentrations between Target and Torch, compared with leaf structural differences, is apparently the most important factor that would affect the infrared color film's tonal response to vegetation in the photographic sensitive region (500 to 900 nm).
 
Hypothetical replanting PPD thresholds for two adjoining planting months.
Seed establishment equation specification and regression statistics.
Estimated rates of survival under various seed treatments and study conditions.
Yield response function specification and regression statistics.
Article
The effect of nine different fungicide seed treatments for soybeans were tested from 2004 to 2007 at Keiser, Stuttgart, and Hope, Arkansas. While seedling emergence was effective across all treatments, only three treatments showed statistically significant differences in partial returns, defined as gross revenue minus seed and seed treatment costs. Comparisons of the regret a producer would experience as a result of non-optimal seed treatment suggested that broad spectrum seed treatment could enhance profitability by an average of $32 per acre with similar treatment recommendations across a range of seeding rates, output prices and study conditions.
 
Article
This article is a history of dryland wheat (Triticum aestivum L.) farming in the low-precipitation (<300 mm annual) region on the Columbia Plateau of the Inland Pacific Northwest (PNW) of the United States. Numerous technological advances, environmental problems, and sociological factors influenced wheat farming since its inception in 1880. The wheat-based economy traces back to the pioneers who faced many challenges that included scarcity of water and wood, unprecedented wind erosion, drought, and minimal equipment. Throughout the years, major technological breakthroughs include: (i) horse (Equus caballus) farming to crude crawler tractors to the 350+ horse power tractors of today, (ii) transition from sacked grain to bulk grain handling, (iii) nitrogen fertilizer and herbicides, (iv) the rotary rodweeder, and (v) the deep furrow split-packer drill to allow early planting of winter wheat into stored soil water. Cultural practices have evolved from repeated passes with high-soil-disturbance tillage implements to today's conservation tillage management. The 2-yr winter wheat–summer fallow rotation continues as the dominant cropping system as it is less risky and more profitable than alternative systems tested so far. Improved wheat cultivars for deep furrow planting continue to be developed with good emergence, disease resistance, winter hardiness, grain quality, and other values. In the past 125 yr, average farm size has grown from 65 to 1400 ha and wheat grain yield increased from <1.0 to 3.4 Mg ha-1. Since the 1930s, government farm programs have provided unwavering support that, in the last several decades, accounts for about 40% of gross farm income.
 
Annual cotton lint yields for the no-N and no-legume treatment (Plot 6), the continuous cotton with only legume N treatment (Plot 8), and the 2-yr rotation + N treatment (Plots 5 and 9). 
Article
After more than 110 yr, the Old Rotation experiment on the campus of Auburn University in Alabama continues to document the long-term effects of crop rotation and winter legume cover crops on sustainable cotton (Gossypium hirsutum L.) production in the southeastern United States. Long-term yields indicate that winter legumes are as effective as fertilizer N in producing maximum cotton yields and increasing soil organic carbon (SOC). Higher SOC resulted in higher crop yields. However, rotating cotton with corn (Zea mays L.) in a 2-yr rotation or with corn, winter wheat (Triticum aestivum L.), and soybean [Glycine max. (L.) Merr.] in a 3-yr rotation produced little long-term cotton yield advantage beyond that associated with SOC. Cotton yields without winter legumes nor fertilizer N are only slightly higher than they were 110 yr ago. Nonirrigated corn grain yields in rotation with cotton are typically low for central Alabama and appear limited by N. Yields of all crops on the Old Rotation increased with increasing rates of P and K through the 1950s. Since adoption of in-row subsoiling, high-residue, conservation tillage, and genetically modified cultivars in 1997, all crops have produced their highest, nonirrigated, recorded yields since the experiment began: 1910 kg cotton lint ha-1 in 2006, 14.8 Mg corn grain ha-1 in 1999, 6.34 Mg wheat ha-1 in 2001, and 4.50 Mg soybean ha-1 in 2004.
 
Precipitation received at the experimental site during 1993, 1994, 2005, and 2006, and long-term means (1908—2008). Data presented as annual and monthly totals, as well as total precipitation for the canola growing season (April—july) and the May through September perIod. 
Measured and simulated [using CROPGRO-canola in Root Zone Water Quality Model, RZWQM23 canoia grain quality parameters (oil and protein content and seed weight). RE relative error [(simuiatedmeasured)imeasured X 100].
Measured (M) and simulated (S) tusins CROPGRO-canola in DSSAT] phenology for 2005 (lIne-source gradient irrigation experiment ISGI) 2006 (LSGI) 993 (ralnout shelter experiment 1105) and l994 1105) irrigatIon experiments at Akron CO 
Article
Currently, canola (Brassica napus L.) is gaining importance as a potential feedstock in biodiesel production industries, increasing the demand for canola production acreage. Agricultural system models that simulate canola growth and yield will help to assess the feasibility of canola production under various agroclimatic conditions. In this study, we adapted the CROPGRO model for simulation of spring canola in both Root Zone Water Quality Model (RZWQM2) and Decision Support System for Agrotechnology Transfer (DSSAT 4.0). Soil water, phenology, leaf area index (LAI), biomass, plant height, and grain yield data from irrigation experiments conducted in 2005 on a Weld silt loam soil (fine, smectitic, mesic Aridic Argiustoll) in the semiarid climate at Akron, CO were used for model parameterization and calibration. Similar data from 1993, 1994, and 2006 were used for validation. Species and cultivar parameters for canola were developed using data from literature or by calibrating the existing CROPGRO-faba bean (Vicia faba L.) parameters. Grain yields across various irrigation levels and seasons were simulated reasonably well by RZWQM2 with root mean square error (RMSE) of 215 kg ha−1 and index of agreement (d) of 0.98. Seasonal biomass development was simulated with RMSEs between 341 and 903 kg ha-1, d between 0.55 and 0.99, and R 2 between 0.85 and 0.98. The CROPGRO-canola parameters developed were also tested within the DSSAT 4.0 cropping systems model and found to produce results with similar accuracy.
 
Article
'Coastal' and 'Tifton 44' (T44) bermudagrass [Cynodon dactylon (L.) Pers.] are well adapted across the lower southern United States, but the grazing response of (T44) to N application in the Piedmont of the upper South warrants further evaluation. This 3-yr experiment compared animal and pasture productivity of Coastal and T44 with three annual N rates of 101, 202, and 303 kg of N ha-1 on a Cecil clay loam (fine, kaolinitic thermic Typic Kanhapludult) soil typical of the Piedmont. Herbage mass differed for Coastal and T44 (3.5 and 3.0 Mg ha-1 respectively, P < 0.01), but not among N rates. The canopy of T44 was leafier (20.6 vs. 14.5% of dry matter) than Coastal and greater for in vitro true organic matter disappearance (IVTOD) (522 vs. 498 g kg-1) and CP (107 vs. 84 g kg-1) and lesser in NDF (596 vs. 605 g kg-1). The diet selected from T44 was greater in IVTOD (764 vs. 743 g kg-1) and lesser in NDF (596 vs. 605 g kg-1) giving greater steer average daily gain (0.63 kg vs. 0.57 kg; P < 0.01) which increased (P = 0.05) with N rate. Weight gain ha-1 (884 kg) and effective feed units (EFU) (4735 kg ha-1) were similar, and N rate linearly increased gain from 723 to 1073 kg ha-1 and EFU from 3978 to 5523 kg ha-1. Soil inorganic N was similar between cultivars but differed among soil depths. Tifton 44 pasture was greater in nutritive value, hence steer performance, and as productive as Coastal in the Piedmont.
 
Article
Use of Tifton 44 bermudagrass [Cynodon dactylon (L.) Pers.] in manure nutrient management is limited to summer haying. This study was done to determine how hay yield and nutrient uptake in a manure-fertilized Tifton 44 field were affected by fall overseeding and spring haying with berseem clover (Trifolium alexandrinum L.), crimson clover (T. incarnatum L.), annual ryegrass (Lolium multiflorum L.), and wheat (Triticum aestivum L.). Overseeding treatments were compared with a nonoverseeded control on Mantachie loam (fine, siliceous, acid, thermic Aeric Fluvaquents) receiving 168 kg P ha-1 in swine (Sus scrofa domesticus) effluent. Spring hay was cut April-June and summer hay July-October 2000-2002. Dry matter (DM) (4.4-5.5 Mg ha-1 yr-1) and P uptake (12.2-17.1 kg ha-1 yr-1) of spring berseem clover hay were higher than the control in 2 of 3 yr and higher than other treatments in 2002. Total DM and P uptake with berseem clover overseeding were 10% higher than the control. Final Mehlich-3 P soil levels (0-5 cm) tended to be lower in the berseem clover treatment than the control (65 vs. 81 mg kg-1, respectively). Spring berseem clover hay was higher in N (94-122 kg ha-1 yr-1) than the control each year and higher than other treatments in 2 of 3 yr. Summer Tifton 44 hay in the berseem clover treatment had more DM in 2002 and higher N uptake in 2001 and 2002 than other treatments. No treatment reduced Tifton 44 yield or nutrient uptake. Overseeding increased hay yield and nutrient uptake, and berseem clover was as good as or better than other treatments.
 
Mean herbage mass and animal –1 and ha –1 performance from steers grazing Coastal and Tifton 44 bermudagrasses at three levels of herbage mass. † 
Article
Hybrid cultivars of bermudagrass [Cynodon dactylon (L.) Pers.] are a major feed source for ruminants across the southeastern United States. This 4-yr experiment compared animal and pasture performance of 'Coastal' and 'Tifton 44' bermudagrasses over three canopy heights designated as short (5.6 cm), medium (10.1 cm), and tall (13.1 cm). The relationship of canopy height to ingestive mastication and canopy characteristics was also studied. Soil was a Cecil clay loam (clayey, Kaolinitic thermic Typic Hapludult). Pastures were continuously stocked using variable stocking to maintain the targeted canopy heights. Herbage mass (to soil surface) was similar between Coastal and Tifton 44 (T44) within each canopy height averaging 2.36, 4.08, and 5.25 Mg ha-1. Steer average daily gain (ADG) was greater (P = 0.09) from T44 than Coastal (0.58 vs. 0.51 kg) but no differences were noted in pasture productivity. Increasing herbage mass linearly increased (P < 0.01) ADG (0.40-0.59 kg) but reduced (P < 0.01) stocking rate (16.1-11.2 steers ha-1), which influenced animal days (1810-1079 d ha-1), weight gain (1057-786 kg ha-1), and effective feed units (6392-4452 kg ha-1). Steer ADG increased (P = 0.01) from short to medium canopy height (0.40-0.64 kg) with little change between medium and tall canopy height (0.64-0.59 kg). Tifton 44 pasture is of greater quality than Coastal giving greater ADG but both were productive producing about 1100 kg of gain ha-1 when effectively managed and utilized.
 
Article
When restoring abandoned pastures on acidic hill-land soils to productivity, it is important to bring soil Ca and Mg to adequate levels. Gypsum is a readily available Ca amendment that is sufficiently soluble to move rapidly into the soil when surface-applied. Gypsum has been shown to reduce detrimental effects of subsurface acidity in soils of the southeastern USA. A 4-yr experiment was initiated to measure effects of surface gypsum application on forage production and to evaluate Mg-containing amendments to avoid gypsum-induced Mg deficiency. The study site was a southern West Virginia Gilpin silt loam (fine-loamy, mixed, mesic, Typic Hapludult) where abandoned hill-land pasture was being restored to productivity. Treatments included 0, 1000, 8000, 16000, and 32000 kg/ha flue gas desulfurization coal combustion by-product gypsum (gypsum) together with dolomitic limestone and five additional treatments to evaluate sources of supplemental Mg. Application of 16000 kg/ha gypsum together with limestone increased forage yields of mixed orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb) pasture during establishment by 42% and production by 11% compared with limestone alone. About 8% of the mean 790 kg/ha yield increase could be attributed to acidity-neutralizing effects of alkaline constituents in the gypsum by-product. Plants in higher gypsum treatments had higher concentrations of K and P, but gypsum application decreased soil and plant Mg concentrations. This indicated that gypsum should not be applied on typical acid soils without supplemental Mg.
 
Article
The rotation of crops with planted, N2-fixing legumes is a promising agroforestry innovation for replenishing soil fertility in the tropics. We postulated that woody and herbaceous legumes with different growth and rooting patterns could be mixed to optimize above- and belowground resource capture. The objective of this study was to evaluate the effect of species interactions on resource utilization by legumes grown in mixtures on a Kandiudalfic Eutrudox in western Kenya. Four woody legume shrubs—pigeonpea [Cajanus cajan (L.) Millsp.], sesbania [Sesbania sesban (L.) Merr.], crotalaria (Crotalaria grahamiana Wight and Arn.), and tephrosia (Tephrosia vogelii Hook F.)—grown in monoculture and mixed stands were evaluated for light interception, soil N and water uptake, and biomass production. Siratro [Macroptilium atropurpureum (DC.) Urb.] and groundnut (Arachis hypogaea L.) were undersown in woody legume stands. Total aboveground biomass production ranged from 9 to 13 Mg ha-1 for monoculture and 8 to 15 Mg ha-1 for mixtures of woody legumes. Total N in woody-legume stands ranged from 100 to 178 kg N ha-1. Biomass and plant N were not significantly different among woody-legume treatments. However, undersowing siratro as a supplement increased stand productivity and recycled biomass N. Species complementarity in topsoil and subsoil utilization of mineral N was observed in crotalaria sesbania and pigeonpea tephrosia mixed stands. Dense soil cover created by siratro led to better conservation of soil water. Results indicated that the tested mixtures provide a better risk management strategy through compensatory growth potential. Greatest opportunities for intensifying resource utilization appear to exist through undersowing a creeping legume with an open-canopy woody legume.
 
Article
Increasing plant species diversity could enhance forage yield, resistance to weed invasion, and soil C accumulation in grazed pastures. Three forage mixtures (2, 3, or 11 species) were established on a farm in eastern Pennsylvania and grazed by dairy heifers or managed under a three-cut hay system from 1999 to 2002. Net canopy photosynthesis was measured from early April to early October 2000 to 2002. Root distribution to a depth of 60 cm was measured in mid-September each year, and soil C and N concentrations to a 15-cm depth were determined in May 1999 and September 2002. The 11-species mixture yielded 43% more forage dry matter than the two-species mixture. This difference was mainly due to the inclusion of a few highly productive forage species in the 11-species mixture. Canopy photosynthesis did not differ among mixtures in the spring, but in the summer was 50% greater in the 3- and 11-species mixtures than the two-species mixture. The 11-species mixture also had 30 to 62% greater root biomass than the other two mixtures and a greater proportion of roots in deeper soil layers. Soil C either remained unchanged or decreased, depending on species composition, with the greatest decrease occurring in the 11-species mixture. No relationship existed between changes in soil C concentration and either canopy photosynthesis or above- and belowground productivity. Deeper rooting could reduce drought stress by increasing access to deep soil moisture. Selecting forage mixtures to include specific desirable traits, such as greater rooting depth, could result in improved pasture performance.
 
Article
Millions of hectares of crops are exposed to wind blown sand abrasion each year, and in many instances the damage is thought to be severe enough to require replanting. The goal of this study was to determine the effects of wind blown sand abrasion duration on cotton (Gossypium hirsutum L.) seedlings. Seedlings of three cotton cultivars were exposed to wind velocities of 13.4 m s-1 with sand abrasive flux density of 0.42 g cm-1 width s-1 for six treatment durations ranging from 0 to 40 min. Plants were destructively sampled at the time of the sand abrasion treatment and also at approximately equal to 2 and 4 wk after exposure. These three sampling dates provided two time intervals for assessing the amount of plant damage and regrowth using classical growth analysis. With increasing sand abrasion treatment time, leaf area and leaf, stem, and total shoot biomass were all reduced while final number of mainstem nodes increased (P <or= 0.05). Cultivar differences in leaf mass were significant only at the second destructive sampling date (P <or= 0.05). For the first harvest interval, between the first and second destructive sampling, shoot relative growth rate (RGR) and net assimilation rate (NAR) decreased with increasing sand abrasion treatment time. Regrowth during the second harvest interval revealed the opposite pattern, with RGR and NAR both increasing with increasing sand abrasion treatment time. In both harvest intervals, variation in RGR depended mainly on NAR rather than leaf area ratio (LAR). These results indicate that, despite near-complete defoliation at the longest treatment duration of 40 min, cotton plants receiving this level of damage in the field may not require replanting.
 
Examples of plant damage for cotton (cv. FM 5013) on 23 Oct. 2006, approximately 3 d following abrasion treatments. From left to right, treatments include no wind and no sand abrasion (Control), wind with no sand abrasion (0 g cm –1 width s –1 ) and wind with sand abrasion (0.10, 0.25. 0.35 and 0.50 g cm –1 width s –1 ). 
Total biomass at three destructive harvests (first, second, and third) vs. sand abrasive flux density. Control treatment (open symbol) was excluded from the indicated regression. Error bars are ± SE. 
Relative growth rate (RGR) and net assimilation rate (NAR) averaged over three cotton cultivars vs. sand abrasive flux density treatment. Control treatment (open symbol) was excluded from the indicated regression. Error bars are ± SE. 
Article
Wind blown soil particle abrasion negatively impacts millions of hectares of crops annually. The goal of this study was to examine the effects of wind and wind blown sand abrasion damage on cotton (Gossypium hirsutum L.) seedling biomass partitioning to leaves, stems, and roots. Seedlings of three cotton cultivars were exposed to no wind (untreated controls) or sand abrasive flux densities of 0, 0.1, 0.25, 0.35, and 0.5 g cm–1 width s–1 at a wind velocity of 13.4 m s–1 in a suction-type laboratory wind tunnel. Plants were destructively sampled at the time of the sand abrasion treatment and at approximately 2 and 4 wk after exposure. These three sampling dates provided two time intervals for assessing the amount of plant damage and regrowth using classical growth analysis. With increasing sand, abrasive flux density, whole plant, leaf, stem, and root biomass, as well as leaf area, were all reduced in both harvest intervals (P <or= 0.05). Net assimilation rate (NAR) accounted for 96 and 75% of the variability in relative growth rate (RGR) in the first and second harvest intervals, respectively, with small but significant differences in leaf area ratio (LAR). Increasing plant damage caused by sand abrasion treatment resulted in preferential biomass partitioning to the damaged stems rather than roots during the first harvest interval, while a much more stable allometric allocation of biomass among plant organs was observed in the second harvest interval.
 
Article
Plant productivity in a community is governed in part by its ability to absorb and utilize photosynthetically active radiation (PAR). Studies on weed competition with a crop for light are limited. The effect of pigweed (Amaranthus hybridus L. and A. palmeri S. Wats) competition on leaf area development, light absorption, and dry matter production of fully developed grain sorghum [Sorghum bicolor (L.) Moench] was evaluated in a field experiment on Pullman clay loam (a fine, mixed, thermic Torrertic Paleustoll) at Bushland, TX, in 1984. Profile measurements (0–0.3, 0.3–0.6, 0.6–0.9, and >0.9 m above ground) of absorbed PAR (APAR) and leaf area index (LAI) by species were taken at four densities of pigweed (0, 1, 4, and 12 plants m⁻²). APAR calculated for sorghum in mixed communities of 1,4, and 12 pigweed plants m⁻² was 79,77, and 49% of the APAR in weed-free sorghum. Sorghum LAI was reduced to 81, 65, and 37% of the LAI of weed-free sorghum in canopies with 1, 4, and 12 pigweed plants m⁻². Sorghum LAI was concentrated in the 0.3- to 0.6-m layer, while the taller pigweed plants had the greatest leaf area concentration above 0.6 m. By absorbing light in the upper canopy, pigweed reduced light penetrating into sorghum. Leaf measurements of photosynthesis and transpiration rates, leaf temperature, and stomatal resistance indicated a relatively minor degree of water stress under full canopy and high potential evaporation conditions; the level of water stress measured was not adequate to explain sorghum dry matter reduction in plots with 1, 4, and 12 pigweed plants m⁻² to 78, 56, and 28% of that in weed-free sorghum. Joint contribution of the USDA-ARS and the Texas Agric. Exp. Stn., Bushland, TX. Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © . .
 
Article
Comparisons between no-till and conventional-till management are often confounded by variation in both tillage and residue placement. The objective of this research was to separate the tillage variable from the surface-residue variable associated with no-till and conventional-till management comparisons in irrigated continuous corn (Zea mays L.) production. Two Nebraska locations (Mead and Clay Center) with differences in soil types and climate were selected. Four tillage-residue treatments [NT-NR (no-till, residue removed), NT-R (no-till, surface residue), T-NR (till, residue removed), T-R (conventional till, surface residue)] were fertilized by either broadcasting at planting or sidedressing at the 6-leaf stage with rates of 0, 56, 112, and 168 kg N ha(-1). At Clay Center, grain yields and total N accumulation were similar for all tillage-residue treatment combinations in all years when the highest fertilizer N rate was used. In 2 of 3 yr at Mead, grain yields and total N accumulation were less for no-till than conventional-till treatments, but in 1 yr the yields and total N accumulations were greater in no-till than conventional-till treatments. At Mead, surface residue resulted in lower grain yields and total N accumulation compared with bare soil at lower N rates, but not at greater N rates, in 2 of 3 yr. Sidedressing fertilizer N was generally a more efficient N placement than broadcasting. Differences between tillage and residue effects at Clay Center and residue effects at Mead were overcome with higher rates of fertilizer N. Tillage effects at Mead did not appear to be N-related. The data suggest that tillage may be necessary to maintain optimum production levels on finer-textured soils when spring soil temperature are cool and slow to warm. When spring soil temperatures are warm, no-till strategies can be used for optimum production levels on these soils.
 
Location effects on spring and summer dry matter accumulation, N concentration, and N removal of winter triticale in Iowa during two growing seasons. Growing degree days were calculated from 1 March using a base temperature of 4 ؇ C. 
Planting date effects on spring and summer dry matter accumulation, N concentration, and N removal of winter triticale in Iowa during two growing seasons. Growing degree days were calculated from 1 March using a base temperature of 4 ؇ C. 
Article
Addition of triticale (xTriticosecale Wittmack) into more diversified cropping systems could provide valuable economic and environmental benefits to producers in the U.S. Corn and Soybean Belt. To maximize triticale value, research was conducted to identify planting dates that allowed maximum dry matter production and N capture. Winter triticale was planted at 10-d intervals from 15 September to 15 October at three Iowa locations: central, northeast, and southwest for two growing seasons: 2002-2003 and 2003-2004. Aboveground dry matter production, N concentration, and N removal were greater at southwest Iowa than central and northeast Iowa. Dry matter production decreased as planting was delayed from late September to late October. Nitrogen accumulation at any time during the spring and summer was greater for September- than October-planted triticale in 2002-2003. At the end of the 2002-2003 season, mid-September-planted triticale had accumulated 37% more N than mid-October-planted triticale. In 2003-2004, total N capture occurring by early May was less for late-October-planted triticale than the other three planting dates, but there were no differences in N capture among the four planting dates from late May until maturity. Dry matter production was greatest when at least 300 growing degree days (GDDs) (base 4 degrees C) accumulated between planting and 31 December. These results suggest that triticale should be planted in September to maximize spring forage yield and N accumulation although later planting dates would provide a higher quality forage if harvest was not delayed into late spring and summer.
 
Article
Low soil water contents may be involved in the lack of success of soybean inoculation in southeastern U.S. soils having high indigenous populations of Rhizobium japonicum. This study was conducted to assess the effect of soil water on the inoculation, biomass, N accumulation, and yield of soybean [Glycine max (L.) Merr.]. 'Bragg' soybeans were noculated with 108 cells/cm row of R. japonicum (strain 110) and grown under both irrigated and nonirrigated conditions on a Norfolk loamy sand (Typic Paleudult) in a split plot design. Rainfall maintained the surface soil above -250 mb matric potential until the late flowering stage of growth. Subsequently, a seasonal drought created treatment differences between irrigated and nonirrigated plots resulting in a twofold increase in seed yield due to irrigation (3,160 vs. 1,682 kg/ha). Inoculation increased the percentage infection by strain 110 from practically 0% background to about 20%. Inoculation increased growth and total N accumulation in pods, petioles, and leaves of Bragg soybeans under irrigated conditions. Under nonirrigated conditions, the increased infection of strain 110 appeared to induced a negative response in the vegetative growth of Bragg soybeans. Nitrogen concentration was also significantly lower in the leaves and pods of nonirrigatedinoculated plants. These differences were not observed in N content of the mature seed, and inoculation did not significantly affect seed yield. These findings indicate that R. japonicum strain x environment interactions may be important for soybean growth and yield in the southeast United States.
 
Article
Amounts and rates of dry matter and nutrient accumulation for very high-yielding corn (Zea mays L.) were unknown, but were needed to develop a base for future research and on-farm maximum economic yield demonstration programs. Aerial whole plant samples, collected from a maximum yield research experiment that resulted in a 19.3 Mg ha-1 grain yield on a Typic Hapludult soil (Freehold sandy loam) near Adelphia, NJ, were used to provide that information. Samples were collected at growth stages V4, V8, V12, VT, Rl, R2, R5, and R6; separated into lower leaves, upper leaves, stem and tassel, and ear and shank fractions; and analyzed to determine N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn concentrations. Accumulation curves for each plant fraction were computed using those data and described mathematically using compound cubic polynomial equations. Dry matter and nutrient accumulation rates were computed by differentiating the equations. Total accumulation at physiological maturity was approximately 31 800, 386, 70, 370, 59, 44, 40,0.13,0.14, 1.9, 0.9, and 0.8 kg ha-' for dry matter, N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn, respectively. Distribution among the four plant fractions, as well as rates of accumulation, are discussed. Diagnosis and recommendation integrated system indices were calculated using leaf concentration data. Nutrient balance was very good, although fertilizer recovery was not optimum. Amounts and rates of accumulation measured in this study can provide general guidelines for very high corn yields when more economical practices are used.
 
Article
In the southeastern Coastal Plain, soybean [Glycine max (L.) Merr.] is normally grown on soils that are often exposed to drought and leaching rains as well as being low in available N. A field study was conducted to evaluate the impact of water management on accumulation of soil and symbiotically fixed N by soybean grown on these type soils. Nodulating and nonnodulating isolines of 'Lee' cultivar soybean were grown under irrigated and nonirrigated conditions in 1979 and 1980 on a Norfolk loamy sand (fine-loamy, mixed, mesic Typic Paleudults). A period of excessive rainfall occurred in 1979, while a major drought occurred in 1980. Irrigated treatments had lower soil-NO-3 concentrations in the Ap horizon than nonirrigated treatments during 1979, but there was no effect of irrigation on soil NO-3 in 1980. Dinitrogen fixation, as estimated by the difference in N accumulation between nodulating and nonnodulating isolines, accounted for 76 to 91% of total plant N in the irrigated plots and 55 to 60% in the nonirrigated plots. Estimates of total plant N fixed exceeded 1100 mg/plant for the irrigated plots in 1979 and 1980. Maximum N accumulation for the nodulating isoline occurred in the nonirrigated plots in 1979 and in the irrigated plots in 1980. However, the nonnodulating isoline had maximum accumulations of both N and dry matter in the nonirrigated treatments in both 1979 and 1980. The number of nodules/plant and the C2H2-reducing activity were significantly higher in the irrigated plots during the pod growth stages in 1980. Irrigation did not significantly affect seed yield of nodulating Lee soybean in 1979, but did result in a twofold increase in 1980. The effects of irrigation on the Lee nonnodulating isoline resulted in a positive yield response in 1980, but a negative response in 1979. These findings show that a major portion of the N-requirement for soybean in the southeastern Coastal Plain is met by fixation and that the relative importance of fixed N may vary substantially with rainfall patterns and irrigation.
 
Aspergillus ear rot data (square centimeters) were generated for inbred lines with a clear plastic grid. 
Fusarium and Aspergillus ear rot data for 20 corn inbreds in 2007 and 2008. 
Aflatoxin and Fumonisin accumulation of 20 inbred lines in 2007 and 2008. 
Fusarium ear rot of 20 inbred lines measured both in square centimeters and with a 1 to 9 rating scale with respect to fumonsin production in 2007 and 2008. 
Aspergillus ear rot of 20 inbred lines measured both in square centimeters and with a 1 to 9 rating scale with respect to aflatoxin production in 2007 and 2008. 
Article
Mycotoxin contamination in corn (Zea mays L.) grain is a worldwide threat to safety of both human food and animal feed. A select group of inbred corn lines was evaluated in field trials for ear rot caused by Aspergillus flavus and Fusarium verticillioides and mycotoxin accumulation in grain. Our goal was to identify lines resistant to both fungi. In separate tests, 20 inbred lines were inoculated with either A. flavus or F. verticillioides. After harvest, ears were rated for rot and evaluated for levels of aflatoxin or fumonisin contamination. Inbred line Mp717 exhibited low grain aflatoxin contamination and it also had the lowest levels of fumonisin. Inbred line Mp317 has been shown previously to have low levels of F. verticillioides kernel infection and fumonisin contamination. Mp317 also had low levels of aflatoxin contamination in this study. Area of the ear rotted by F. verticillioides and A. flavus was significantly correlated to toxin production for both fumonisin (P = 0.0002; r = 0.74) and aflatoxin (P = 0.004; r = 0.61), indicating that inbreds exhibiting aflatoxin resistance may also be good sources of fumonisin resistance. Our method of quantifying ear rot may also be used to rapidly screen lines for A. flavus resistance and subsequent aflatoxin accumulation in preliminary evaluations.
 
Schematic of condensate collection system. 
The hourly dynamics of profile water volume in the six treatments from TDR water content data from the period 21 to 24 July 2005 (41-44 DAE).
Article
The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity environment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give information on soil water status or root activity. The objective of this study was to compare ET measurements from the condensate system with ET calculated from measurements of water content by TDR. Data from an irrigation x carbon dioxide (CO2) study on potato (Solanum tuberosum L.) were used for this study. The soil water contents in the growth chamber soilbins were monitored once an hour at five vertical depths with three measurement locations per depth using an automated TDR system. The correspondence between daily ET rates for the two systems was good. Maximum daily ET rates were near 6.1 to 7.1 mm cm-2 d-1 (7-8 L d-1 on a chamber basis) and differences were on the order to 0.89 to 1.8 mm cm-2 d-1 (1-2 L d-1). At the higher daily ET rates, the daily values from the two methods were closer. The correspondence between hourly measurements of ET measured from the condensate system and calculated from TDR water contents was poor due to instrument and soil variability. A significant source of error was vertical variation in water content in the soil between horizontally placed TDR probes, especially during irrigation events. Evapotranspiration estimates from TDR measurements were much more robust for calculation of water use over a period of time. Data from the condensate system were most useful for quantification of diurnal transpiration rates and were better correlated with radiation.
 
Article
Nitrogen fixation and accumulation are important facets of soybean (Glycine max L.) production. Three determinate soybean cultivars were grown on a Norfolk loamy sand (Typic Paleudult) with either conservation or conventional tillage. Plots were split for inoculation with strain 3I1b 110 of Rhizobium japonicum. Dinitrogen fixation was estimated by the difference between total shoot N for nodulating and nonnodulating 'Lee' isolines, and net N returned to the soil was estimated by the difference in dinitrogen-fixed N and seed N. Drought was significant the first year; only 19.5 cm of rain fell during the podfill period. Rainfall and soil water were adequate the second year. Tillage, cultivar, and inoculation did not consistently affect the percentage of nodules formed by particular rhizobia1 strains, individually, but specific treatment combinations significantly affected nodular occupancy by certain strains. Inoculated 'Coker 338' had the highest shoot total N accumulation in both years; however, the difference between years overshadowed tillage, cultivar, or inoculation effects. For the 2-y period, percentages of N supplied by N2 fixation were estimated to be 58 to 67% and 49 to 65% under conservation and conventional tillage, respectively. Yields generally did not differ significantly for tillage or inoculation; however, Coker 338 soybean was lowest in seed yield even though it had the highest total N accumulation in the shoots. Estimates of net N returned to the soil varied more between years than between tillage treatments; values ranged from 14 to 40 kg ha-1 in 1980 and 57 to 123 kg ha-1 in 1981.
 
Mean daily maximum and minimum temperatures and mean daily herbage accumulation of three bahiagrass entries during each growth period of 15 or 30 d during (a) 1993-1994 and (b) 1994-1995 at Ona, FL and (c) 1993-1994 and (d) 1994-1995 at Tifton, GA.
Mean daily herbage accumulation of three bahiagrass entries during each growth period of 15 or 30 d during (a) 1993-1994 and (b) 1994-1995 at Ona, FL and (c) 1993-1994 and (d) 1994-1995 at Tifton, GA. Within sampling dates, means accompanied by different letters are significantly different (P 0.05); ns, not significantly different.
Mean in vitro organic matter disappearance (IVOMD) of three bahiagrass entries during each growth period of 15 or 30 d during (a) 1993-1994 and (b) 1994-1995 at Ona, FL and mean in vitro dry matter disappearance (IVDMD) of each of three bahiagrass entries during (c) 1993-1994 and (d) 1994-1995 at Tifton, GA. Within sampling dates, means accompanied by different letters are significantly different (P 0.05); ns, not significantly different.
Mean crude protein (CP) of each of three bahiagrass entries
Article
Fall and winter are periods of critical forage shortage in subtropical regions of the world, including the extreme southeastern USA. Cool-season herbage accumulation has not been documented for bahiagrass [Paspalum notatum Flugge var. saurae Parodi] that has been selected using recurrent restricted phenotypic selection (RRPS) for increased warm-season yield. Regrowth of 'Pensacola', 'Tifton 9', and RRPS Cycle 18 that accumulated for 15 or 30 d was harvested from mid-September through mid-April at Tifton, GA and Ona, FL for 2 yr. Herbage accumulation was essentially parallel for the three populations; minimums were coincident in midwinter, and maxima generally occurred at the first autumn harvest or last spring harvest. Fall and spring yields of Tifton 9 and RRPS Cycle 18 were generally higher than those of Pensacola and often more than double. This advantage was more pronounced at Ona than Tifton. Digestibility (600 g kg(-1)) and crude protein (CP) concentration (150 g kg(-1)) at Ona remained high throughout the cool season. However, forage quality of bahiagrass at Tifton tended to decrease with increased frosts. Cool-season growth of three bahiagrass populations was slow, but RRPS selection has led to populations with greater growth potential, except when cold temperatures prohibit growth entirely.
 
Intra-annual coefficients of variation for crude protein, neutral detergent fiber (NDF), and in vitro true digestibility (IVTD) of forage mixtures in 2002 and 2003. Two species: orchardgrass, white clover; three species: orchardgrass, white clover, chicory; six species: orchardgrass, tall fescue, perennial ryegrass, red clover, birdsfoot trefoil, chicory; and nine species: the six-species mixture plus white clover, alfalfa, and bluegrass. 
Botanical composition of herbage from pastures of four forage mixtures during spring, summer, and autumn of 2002 and 2003 at University Park, PA. Data points are averages of five or six sampling dates within growth periods and two replicate pastures. Bars indicate ± one standard error. 
Article
Planting forage mixtures may benefit pasture herbage production; however, changes in botanical composition could cause variable (unstable) nutritive value. A grazing study was conducted to compare forage mixtures for variation in herbage nutritive value with time and herbage accumulation rate. In August 2001, four mixtures (two, three, six, and nine species of grasses, legumes and chicory, Cichorium intybus L) were established in replicated 1-ha pastures (eight total) in central Pennsylvania. Pastures were grazed by dairy cattle (Bos taurus) from April to September of 2002 and 2003 and sampled frequently for nutritive value and herbage accumulation rate in April, July, and September each year. The intra-annual variation (across all sampling periods within years) in fiber and digestibility was similar among mixtures; however, variation in crude protein (CP) was greater for the six-species mixture than others in 2003. Concentration of CP (range of 155–250 g kg–1 dry matter) seemed to be controlled by herbage legume proportion (Pearson r of 0.33–0.90), whereas fiber (range of 278–506 g kg–1) and digestibility (range of 740–895 g kg–1) were controlled by the grass proportion (Pearson r of 0.54–0.88). The three-, six-, and nine-species mixtures (all with chicory) had greater herbage accumulation rates than the orchardgrass (Dactylis glomerata L.)-white clover (Trifolium repens L.) mixture in 2002, a dry year. Accumulation rates were similar among mixtures (avg of 62 kg ha–1d–1 in spring and 47 kg ha–1d–1 in summer) in 2003 with more rainfall. Complex forage mixtures were not inherently unstable in herbage nutritive value.
 
Article
Applying organic amendments to cropland affects corn (Zea mays L.) response to tillage systems differently. Identifying causes of the tillage by amendment interaction could match amendment inputs to responsive tillage systems. The objectives of this research were to determine if shoot dry matter (DM), nutrient uptake, and soil water use could explain the tillage by compost interaction for corn-grain yield. A corn-soybean [Glycine max (L.) Merr.]-wheat (Triticum aestivum L.)/clover (Trifolium spp.) rotation, in all phases, with or without compost amendment, was initiated in 1998 in plots that had been managed with moldboard plow (MP), chisel plow (CT), or no-tillage (NT) since 1988. Compost amendment increased corn whole-plant P and K uptake 19 and 21%, averaged across 2 yr. No-tillage increased whole-plant P uptake 1 yr compared to MP and CT (113 vs. 65 kg ha-1) and increased grain P concentration (3.1 vs. 1.5 g kg-1). Compost provided no benefit (2 yr) or a negative effect (1 yr, 22%) to corn yield in MP. Compost provided no benefit to corn yield in CT. Corn growing in NT derived no benefit (2 yr) or a positive (1 yr, 9%) effect on grain yield from compost amendment. The tillage and compost responses observed in this study cannot be explained by plant N, soil water use, leaf gas exchange, or DM partitioning. Grain yield from soil managed using NT may respond to compost amendment, but reasons for this response remain unclear.
 
Article
Reports on accumulation and distribution of nutrients by determinate soybeans [Glycine max (L.) Merr.] when grown under field conditions have seldom included information about micronutrients or made comparisons among several cultivars grown with or without irrigation. To provide this information, we grew three or four determinate soybean cultivars with or without irrigation on a Norfolk loamy sand (fine-loamy , siliceous thermic Typic Paleudults) during 1978 and 1979. Plant samples were collected periodically throughout the growing season to measure dry matter accumulation and distribution among the leaves, petioles, stems, and pods. Plant fractions were analyzed for P, Fe, Mn, and Zn. Total P accumulation reflected total dry matter production and was greater in plants which received irrigation during periods of water stress. The total P and Zn accumulation among cultivars was generally not significantly different, although the P and Zn concentrations in the cv. Ransom were frequently higher. The concentrations and accumulations of Fe and Mn were generally not influenced by cultivar. Irrigation appeared to enhance P diffusion to plant roots and increased P concentrations at some samplings, but it rarely influenced Fe, Mn, or Zn concentration or accumulation. Total P, Fe, Mn, and Zn accumulations were greater during 1979 due to earlier planting, a shorter period of drought, and more available soil water in the lower part of the profile. Accumulation of these nutrients reflected plant growth, but seed yields did not follow the same pattern. With irrigation, 1979 seed yields averaged 1.95 metric tonsha compared to average irrigated yields of 3.16 metric tons/ha in 1978. Nonirrigated yields averaged 1.72 and 1.62 metric tons/ha in 1978 and 1979, respectively. Seed yields did not appear to be limited by P or micronutrient accumulation. Also, for these determinate cultivars yields were not closely related to total dry matter production.
 
Article
Biomass and nutrient accumulation data have often been obtained to determine rates of nutrient uptake. Traditionally calculated as the difference in accumulation divided by elapsed time, rate values thus obtained are slopes of linear interpolations between points on the accumulation curve. That implies an assumption of constant uptake rate during the observation period. Our objective was to illustrate a higher-order interpolant that is not subject to such assumptions. With it, one obtains smooth curves consistent with the assumption that daily uptake rates are somewhat related. The abrupt changes in rates determined with linear interpolation are consistent with daily rates that are unrelated. Analyses of historical and recent data showed that additional information may be obtained from higher-order analysis methods. Cubic interpolation methods were applied to the accumulation curve to obtain continuous, smooth nutrient uptake curves. The programs used are described, and two sample data sets of corn (Zea mays L.) growth and N accumulation illustrate the strengths, weaknesses, and inherent assumptions of this analytical technique. In general, this technique can be used if the objective is to analyze intraseasonal variation in growth or uptake rates determined from sparse data.
 
Article
The maximum amount and rate of nutrient accumulation by irrigated corn (Zea mays L.) must be known so that farmers do not waste money or pollute water resources by applying excessive amounts of fertilizer. Aerial whole plant samples were therefore collected from irrigated field experiments conducted on Norfolk (Typic Paleudults) loamy sand in 1980, 1981, and 1982, to determine seasonal dry matter, N, P, and K accumulations for corn yielding 10 Mg ha-1 or more in the southeastern Coastal Plain. Rates of accumulation were derived by differentiating compound cubic polynomial equations that described seasonal accumulation patterns. Total dry matter accumulation averaged 23.1 and 24.9 Mg ha-1 for two population treatments that averaged 7 x l04 or 10 x l04 plants ha-1. Aerial N, P, and K accumulation respectively averaged 228,58, and 258 kg ha-1 in 1980; 264,37, and 372 kg ha-1 in 1981; and 225,37, and 335 kg ha-1 in 1982. Grain yields averaged 13.4, 11.7, and 10.9 Mg ha-1 in 1980, 1981, and 1982, respectively. Lower P accumulations in 1981 and 1982 were the result of lower grain yields that were apparently caused by excessive K accumulation. Calculated peak dry matter, N, P, and K accumulation rates were 650, 10, 1.6, and 28 kg ha-1 day-1 in this study, compared to rates of 247,4.5,0.6, and 3.2 kg ha-1, respectively, in previous midwestern studies. Peak accumulation rates during both vegetative and reproductive growth stages emphasize that cultural, nutrient, and water management practices must be coordinated to provide a minimum stress production environment for high corn yield.
 
Changes in water use efficiency (WUE) as affected by seasonal
Article
Water use efficiency (WUE) represents a given level of biomass or grain yield per unit of water used by the crop. With increasing concern about the availability of water resources in both irrigated and rainfed agriculture, there is renewed interest in trying to develop an understanding of how WUE can be improved and how farming systems can be modified to be more efficient in water use. This review and synthesis of the literature is directed toward understanding the role of soil management practices for WUE. Soil management practices affect the processes of evapotranspiration by modifying the available energy, the available water in the soil profile, or the exchange rate between the soil and the atmosphere. Plant management practices, e.g., the addition of N and P, have an indirect effect on water use through the physiological efficiency of the plant. A survey of the literature reveals a large variation in measured WUE across a range of climates, crops, and soil management practices. It is possible to increase WUE by 25 to 40% through soil management practices that involve tillage. Overall, precipitation use efficiency can be enhanced through adoption of more intensive cropping systems in semiarid environments and increased plant populations in more temperate and humid environments. Modifying nutrient management practices can increase WUE by 15 to 25%. Water use efficiency can be increased through proper management, and field-scale experiences show that these changes positively affect crop yield.
 
Analysis of varance for total saturated fatty acids at four locations in Mississippi. 
Article
The fatty acids (FA) composition of sunflower (Helianthus annuus L.) determines its uses and health effects on humans, while oil content determines the price paid to producers. The hypothesis of this study was that agronomic factors (genotype, planting date, and N rate) will affect total saturated fatty acid (TSFA) concentration and oil content of sunflower. Additionally, Mississippi-grown sunflower will have a different FA composition than the original seeds produced in more northern latitudes and used for planting. A field experiment was performed in four locations in Mississippi (Newton, Starkville, and two locations in Verona) to assess the effect of planting date (20 April, 20 May, and 20 June), N application rate (0, 67, 134, and 202 kg N ha-1) and genotype (hybrid, DKF3875, DKF2990, DKF3510, and DKF3901) on sunflower seed oil content and composition. The TSFA and oil content were significantly affected by planting date, hybrid, and N rate. Overall, later planting dates increased TSFA relative to the first planting, and in most instances TSFA concentrations in sunflower from the third planting was higher than in seeds from the second. Generally, the first planting date provided the highest oil content of the four hybrids, the second planting reduced oil content, while the third was not different from the second. Our results suggest that an earlier planting date may reduce the TSFA and increase oil content of sunflower in Mississippi. Regarding individual FA, overall, palmitic (16:0) and stearic acid (18:0) concentrations in sunflower seed grown in Mississippi from the first planting were reduced relative to the respective concentrations in the original seed. Later planting tended to increase these two acids relative to the first planting and relative to the original seed. The three minor saturated fatty acids (SFA), arachidic (20:0), behenic (22:0), and lignoceric acid (24:0) followed a similar pattern. This study demonstrated that agricultural factors such as planting date, hybrid, and N rate may significantly modify FA composition and oil content of sunflower grown in Mississippi, suggesting that these could be used as management tools for decreased TSFA and increased oil content.
 
Article
Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997-2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (less than or equal to 5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.
 
Trends in crude protein (CP) of 10 tall fescue cultivars across
Trends in (a) dry matter yield and (b) total protein yield for Fig. 3. Trends in (a) neutral detergent fiber (NDF) and (b) in vitro 10 tall fescue cultivars across five water levels (WLs) at three true digestibility (IVTD) for 10 tall fescue cultivars across five water harvests. The LSD (0.05) values for differences among harvests for levels (WLs) at three harvests. The LSD (0.05) values for differences dry matter yield were 456, 415, 533, 313, and 491 kg ha 1 at WL-1 among harvests for NDF were 11.1, 9.7, 6.9, 7.4, and 9.5 g kg 1 at through WL-5, respectively. Corresponding LSD (0.05) values for total WL-1 through WL-5, respectively. Corresponding LSD (0.05) values protein were 80, 84, 97, 73, and 82 kg ha 1. for IVTD were 2.8, 6.1, 2.9, 4.1, and 5.4 g kg 1 .
Article
Water available for irrigating pastures in the western USA is often limited and varies widely across sites and seasons. Objectives were to determine the trends in crude protein (CP), neutral detergent fiber (NDF), and in vitro true digestibility (IVTD) of 10 cultivars of tall fescue (Festuca arundinaceae Schreb.) at five levels of irrigation and three harvest dates (early, mid-, and late season). A secondary objective was to evaluate the effect of the endophytic fungus [Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon & Hanlin] on these trends. Cultivars differed significantly for CP, NDF, and IVTD, and differences were generally consistent across water levels (WLs). Concentration of CP increased in a near linear manner (154-189 g kg(-1)) from the highest to lowest WL; however, total protein yield decreased from 611 to 447 kg ha(-1) with less water, closely following the trend in forage yield. Forage quality at the late-season harvest, as indicated by lower NDF and higher IVTD values, was significantly higher at the lowest compared with the highest WL. Also, NDF was significantly lower and IVTD significantly higher at the late-season harvest at all WL. Presence or absence of the endophyte was not associated with CP; however, there was a tendency for the endophyte-free cultivar to have lower NDF and higher IVTD than its endophyte-infected counterpart at the higher WL. The magnitude of quality differences among the 10 cultivars indicates that forage quality should be a major consideration in the choice of cultivars for pastures of the Intermountain region.
 
Soil apparent electrical conductivity (EC a ) map of the relative depth to the claypan layer. Circles represent sampling points for soil water content and lines represent contour lines with elevation expressed in meters above sea level. 
Daily (bars) and cumulative precipitation (segmented line) for the growing season from planting to grain harvest in (A) 2005 and (B) 2006. Arrows show the time of planting, fertilizer application, and grain harvest. 
Comparison of gravimetric soil water content at a depth of 0 to 10 cm at different landscape positions over the growing season in (A) 2005 and (B) 2006. Vertical bars show the LSD (0.05) values at each sampling time; NS = not significant. 
Gross profit differences in low-lying areas at 168 kg N ha –1 of (A) anhydrous ammonia (AA) or (B) polymer- coated urea (PCU) fertilizer compared with urea at different crop prices. Each line on the graph represents possible fertilizer cost differentials between AA or PCU and urea. Positive fertilizer cost differentials indicate AA or PCU cost was greater than urea, whereas a negative cost differential indicates AA or PCU cost was less than urea. Possible application cost differences among the N fertilizer sources were not included in the analysis. A fertilizer price differential of $0.44 kg –1 N is equivalent to $0.20 lb –1 N. Corn grain prices used in this analysis ranged from $0.08 to $0.31 kg –1 ($2 to $8 bu –1 ). 
Article
Improvement of N fertilizer recovery efficiency (NRE) is necessary to reduce excess N entering the environment and to increase economic returns. A 2-yr field trial was established in 2005 in Northeast Missouri to determine the effects of conventional and slow-release N fertilizer sources and landscape position (summit, sideslope, and low-lying) on crop growth and NRE in corn (Zea mays L.) in a claypan soil. Nitrogen fertilizer treatments at 168 kg N ha-1 consisted of pre-plant applied and incorporated polymer-coated urea (PCU), urea, 50% PCU/50% urea mix by weight, anhydrous ammonia (AA), and a nontreated control. Gravimetric soil water content data in 2005 and 2006 indicated that the low-lying position was often wetter than the summit and sideslope positions. Anhydrous ammonia and PCU treatments increased grain yield 1470 to 1810 kg ha-1 over urea in the low-lying position in 2005 and 2006. Corresponding increases in plant N uptake and NRE were observed in the low-lying position in 2005 with use of PCU and AA compared to urea, but not in 2006. Based on the grain yield results in this research and different fertilizer cost and crop prices, gross profit differences for use of PCU and preplant-applied AA compared with urea in the low-lying position could range from $50 to $642 ha-1. These results demonstrate that targeted use of different N fertilizer sources in claypan landscapes may increase grain yields and profitability.
 
Article
Functional genomics is the systematic study of genome-wide effects of gene expression on organism growth and development with the ultimate aim of understanding how networks of genes influence traits. Here, we use a dynamic biophysical cropping systems model (APSIM-Sorg) to generate a state space of genotype performance based on 15 genes controlling four adaptive traits and then search this spice using a quantitative genetics model of a plant breeding program (QU-GENE) to simulate recurrent selection. Complex epistatic and gene X environment effects were generated for yield even though gene action at the trait level had been defined as simple additive effects. Given alternative breeding strategies that restricted either the cultivar maturity type or the drought environment type, the positive (+) alleles for 15 genes associated with the four adaptive traits were accumulated at different rates over cycles of selection. While early maturing genotypes were favored in the Severe-Terminal drought environment type, late genotypes were favored in the Mild-Terminal and Midseason drought environment types. In the Severe-Terminal environment, there was an interaction of the stay-green (SG) trait with other traits: Selection for + alleles of the SG genes was delayed until + alleles for genes associated with the transpiration efficiency and osmotic adjustment traits had been fixed. Given limitations in our current understanding of trait interaction and genetic control, the results are not conclusive. However, they demonstrate how the per se complexity of gene X gene X environment interactions will challenge the application of genomics and marker-assisted selection in crop improvement for dryland adaptation.
 
Article
Cold, wet soils, coupled with a short growing season, create a narrow window of optimum time for planting corn (Zea mays L.) in the northern Corn Belt. Temperature-activated polymer (TAP) coatings designed to inhibit planted seed from imbibing water until adequate soil temperatures are reached to promote germination and emergence may offer potential for planting corn exceptionally early. A study from 2000 to 2002 was conducted in west central Minnesota on a Barnes soil (Calcic Hapludoll) to determine the potential for earlier-than-average planting of TAP-coated corn seed. The objective was to compare emergence characteristics of coated and uncoated hybrid corn planted early and at a near-average planting date. Seed planted 29 Mar. 2000 and 24 Apr. 2002 remained in the soil for as long as 26 to 32 d before emerging. In these instances, stands from TAP-coated seed, which ranged from 60 to 90% of seed planted, were generally greater than those of uncoated seed, which ranged from 49 to 68%. Stand establishment and time required to obtain 50% and from 10 to 90% emergence for most early planted coating x hybrid seed combinations were similar to uncoated seed planted at near-average planting dates of 1, 14, and 16 May in 2000, 2001, and 2002, respectively. When both coated and uncoated seed were sown at an average planting date, stand establishment was similar, but emergence for coated seed was generally delayed. Results of this study indicate that TAP coatings protected seeds from injury caused by extended exposure to cold soils, and therefore, might be a useful management tool for early corn planting.
 
Top-cited authors
J.s. Schepers
  • University of Nebraska at Lincoln
Pasquale Steduto
  • Food and Agriculture Organization of the United Nations
Jerry Hatfield
  • United States Department of Agriculture
Theodore C Hsiao
  • University of California, Davis
E. Fereres
  • University of Cordoba (Spain)