Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2001
Publication Date: 3/1/2003
Citation: WANG, D., PRATO, T., QIU, Z., KITCHEN, N.R., SUDDUTH, K.A. ECONOMIC AND ENVIRONMENTAL EVALUATION OF VARIABLE RATE NITROGEN AND LIME APPLICATION FOR CLAYPAN SOIL FIELDS. PRECISION AGRICULTURE. 2003. V. 4. P. 35-52. Interpretive Summary: Higher fossil fuel prices have recently caused nitrogen (N) fertilizer costs to nearly double from a year ago. This, along with increasing environmental concern for how agricultural use of N is affecting life in streams, rivers, and the ocean, has motivated farmers to consider how N fertilizers can be managed more efficiently. Precision farming (sometimes called site-specific farming) methods, which adjust inputs to match crop needs, is one proposed way of more efficiently managing N. This study was based on measurements of the variability of claypan soil topsoil thickness (a basis for variable-rate N applications) and soil pH (a basis for variable-rate lime applications) on four fields in Missouri. Using the known variability from these case study fields, yield response and left- over soil N were predicted for several variable-rate methods and two conventional single-rate methods and then compared for profitability and environmental effects. Results of this analysis showed that variable-rate was generally more profitable and led to less unused N than most single- rate applications. A sensitivity analysis indicated that profitability and potential water quality benefits of variable-rate management increased with greater variability in topsoil depth and/or soil pH. The results were more sensitive to measures of variability (e.g., standard deviation in topsoil depth and soil pH) than to field averages of these variables. The results of this study will benefit farmers and crop consultants by helping them understand that the nature and magnitude of variability within fields establishes the likelihood of benefits from variable-rate methods. Careful characterization of field variability is needed for developing site- specific plans that are more efficient and environmentally friendly.
Technical Abstract: Variable rate technology (VRT) has the potential to increase crop yields and improve water quality relative to uniform rate technology (URT). The effects on profitability and water quality of adopting VRT for nitrogen (N) and lime were evaluated for corn production on four claypan soil fields in north-central Missouri. Variable N and lime rates were based on measured topsoil depth and soil pH, respectively. VRT rates were compared to two different uniform N applications (URT-N1 and URT-N2). Expected corn yield was predicted based on topsoil depth, soil pH, N rate, and lime rate. Water quality benefits of VRT relative to URT were evaluated based on potential leachable N. Sensitivity analyses were performed using topsoil depth and soil pH. Results showed that VRT was more profitable than URT in the four sample fields under URT-N1 and in two of the four fields under URT-N2. Better water quality was indicated under VRT than either URT strategy for all sample fields. Greater variation in topsoil depth and soil pH resulted in higher profitability and greater water quality benefits with VRT. Results support adoption of VRT for N and lime application on claypan soils in the study area.