James S. Schepers

Simultaneous determination of total C, total N, and 15N on soil and plant material

Abstract Availability of labor and laboratory instrumentation has frequently limited use of isotopes in N management research. Recent innovations in laboratory instrumentation have made it possible to simultaneously determine total C, total N, and 15N concentrations in plant, soil, and water samples. An automatic C and N analyzer was interfaced with a continuous‐flow mass spectrometer for purposes of routine analytical determinations. Compared to manual procedures, the automated procedure was rapid, accurate, and gave reproducable results both over time and between adjacent samples. Ball‐mill preparation of samples greatly increased precision of determinations and is recommended to improve sample homogeneity.

Biological Resource Management Connecting Science and Policy

Jointly published with INRA, Paris.The application of new production methods in the food industry - genetic engineering in plants and animals - as well as recent crises over food-borne diseases have led consumers to a growing concern about science as an appropriate basis for developing sound agricultural policies. This book presents the discussion of scientists and politicians in the framework of an OECD programme conference on how to restore public trust in the application of new scientific achievements concerning food production.

Comparison of Ground‐Based Remote Sensors for Evaluation of Corn Biomass Affected by Nitrogen Stress

Abstract The nondestructive determination of plant biomass is not possible; however, crop‐canopy sensors that determine the normalized difference vegetation index have the potential to estimate living biomass, which is indicative of plant vigor and stress. Pot experiments using sand culture were conducted in 2002 and 2003 under greenhouse conditions to evaluate the effect of nitrogen (N) deficiency on corn biomass and reflectance. Stress was imposed by implementing six to eight levels of N in Hoaglands nutrient solution. Canopy reflectance measurements made at three growth stages with a variety of handheld spectral sensors (active and passive) were closely correlated with dry weight and chlorophyll meter readings of corn at flowering, as well as at the two earlier growth stages. Results indicate that selected ground‐based sensors and related reflectance indexes can provide a nondestructive, real‐time assessment of apparent plant N status and thus be used for in‐season N‐management decisions.

Role of nitrogen mineralization in fertilizer recommendations

Abstract Efficient use of nitrogen (N) fertilizer is important to achieve optimum crop yields while avoiding potential contamination of surface and ground water. A major obstacle in achieving optimum N fertilization is the difficulty of predicting soil organic N mineralization under field conditions. Since soils differ in their N‐supplying capacity, there is need for a testing procedure that will enable producers to make an accurate assessment of soil N availability. The purpose of this study was to evaluate electro‐ultrafiltration (EUF) and autoclave techniques to estimate soil N mineralization relative to N uptake by corn from unfertilized plots. Five different geographical locations in Nebraska were selected to encompass climatic conditions and soil types typically encountered throughout the state. Soil organic N mineralized determined by plant N uptake varied between geographical locations and ranged from 13 to 131 kg ha‐1. Data from both laboratory procedures were poorly correlated with crop N uptake...

Estimation of surface soil organic matter using a ground-based active sensor and aerial imagery

Active canopy sensors are currently being studied as a tool to assess crop N status and direct in-season N applications. The objective of this study was to use a variety of strategies to evaluate the capability of an active sensor and a wide-band aerial image to estimate surface soil organic matter (OM). Grid soil samples, active sensor reflectance and bare soil aerial images were obtained from six fields in central Nebraska before the 2007 and 2008 growing seasons. Six different strategies to predict OM were developed and tested by dividing samples randomly into calibration and validation datasets. Strategies included uniform, interpolation, universal, field-specific, intercept-adjusted and multiple-layer prediction models. By adjusting regression intercept values for each field, OM was predicted using a single sensor or image data layer. Across all fields, the uniform and universal prediction models resulted in less accurate predictions of OM than any of the other methods tested. The most accurate predictions of OM were obtained using interpolation, field-specific and intercept-adjusted strategies. Increased accuracy in mapping soil OM using an active sensor or aerial image may be achieved by acquiring the data when there is minimal surface residue or where it has been excluded from the sensor’s field-of-view. Alternatively, accuracy could be increased by accounting for soil moisture content with supplementary sensors at the time of data collection, by focusing on the relationship between soil reflectance and soil OM content in the 0–1xa0cm soil depth or through the use of a subsurface active optical sensor.

New diagnostic tools for tissue testing

Abstract Diagnostic procedures that identify nutrient deficiencies and excesses in crops will likely gain prominence in the future. One reason is environmental concerns are driving producers to more timely and judicious use of fertilizers and waste products. Economics is an equally important factor that ultimately dictates producer practices. Advancements made in global positioning systems (GPS), geographical information systems (GIS), and variable rate application technology (VRAT) have made it possible to make nutrient management practices more site specific and reduce losses through runoff and leaching. These technologies open many opportunities for tissue testing because as whole‐field fertilizer application practices become more closely scrutinized, and nutrient deficiencies will become more obvious. Diagnosing these deficiencies will likely involve a combination of new technologies, such as on‐the‐go yield monitoring devices and aerial photography to identify problem areas in fields. Various analyti...

USE OF PRECISION FARMING TO IMPROVE APPLICATIONS OF FEEDLOTWASTE TO INCREASE NUTRIENT USE EFFICIENCY AND PROTECTWATER QUALITY

Spatial variability in crop yields can be caused by many factors, which makes it difficult to determine the most limiting factors. Application of animal wastes to relatively infertile areas offers the potential to supply needed nutrients and improve soil physical properties. The objectives of this study were to test a manure application strategy to reduce spatial variability in corn (Zea mays L) yield and to identify the most limiting nutrients in relatively low yielding areas in a field. Fresh solid beef feedlot manure was applied in 1997 to a strip across areas with variable fertility status. No fertilizer was applied with the manure in 1997. Uniform N fertilizer, but no manure, was applied in 1998. Leaf tissue samples and chlorophyll meter readings were collected along the strips during the growing season and from adjacent strips without manure application. Grain yield was determined at plant maturity. In 1997, chlorophyll meter readings indicated season long N deficiency (<95% sufficiency index) in no-manure plots with sufficiency indices of 93, 88, 85, and 88% for the V10, V17, R2, and R3 growth stages, respectively. Only an early season N deficiency was detected in a few of the no-manure plots in 1998. Leaf tissue analyses indicated N and P were growth limiting factors in 1997, with leaf N concentrations of 25, 26, and 27 mg g−1 for non-manure plots and 30, 33, and 31 mg g−1 for manure plots at V12, R1, and R3 growth stages, respectively. Leaf P concentrations were 2.0, 2.0, and 1.9 mg g−1 for no-manure plots versus 2.5, 2.7, and 2.3 mg g−1 for manure plots, respectively. In 1998, neither N or P were identified as limiting factors. Grain yields in 1997 were 10.2 and 12.2 Mg ha−1, which increased to 11.9 and 12.8 Mg ha−1 in 1998 for no-manure and manure plots, respectively.

Comparison of early season stem nitrate and leaf total nitrogen concentrations across corn hybrids

Abstract Basal stem nitrate‐N concentration in young maize plants has been proposed as a method to evaluate soil nitrogen (N) adequacy for near maximum yields. While plants are usually considered good integrators of soil N availability, adoption of tissue testing procedures to evaluate crop N status may depend on metabolic differences between maize cultivars. Research was initiated to evaluate if there are cultivar induced differences in basal stem nitrate‐N concentration and total N concentration in maize leaves at the V6 growth stage. A nitrification inhibitor (nitrapyrin) was incorporated into split plots at planting to create two inorganic N regimes. Large variations in basal stem nitrate concentration within hybrids precluded detection of differences between hybrids for either year of the study as a result of the nitrification inhibitor. In contrast, leaf N concentration was different between hybrids for both years, but was not affected by nitrapyrin treatment. Cultivar selection based on leaf N conc...