Submitted to: National Workshop on Constructed Wetlands/BMPS for Nutrient Reduction and ...
Publication Type: Proceedings
Publication Acceptance Date: 9/8/1999
Publication Date: N/A
Technical Abstract: Crop nitrogen (N) needs are complex and difficult to predict since climate, soil, and management factors interact differently for each cropping season. Because of this uncertainty and low N fertilizer costs, many cropped acres are fertilized at "insurance" rates, meaning the amount of N fertilzer applied will be sufficient for the most N-demanding years (i.e., temporal variability) and soil types (i.e., spatial variability). Application of N fertilizer using precision agriculture strategies has the potential of improving crop-use efficiency of fertilizer by minimizing over- and under- application. In 1992 research was initiated with combine yield monitoring of Missouri MSEA project research plots and fields near Centralia, MO. Concurrent investigations found that apparent soil electrical conductivity (EC) using an EM38 electromagnetic induction instrument could be used to accurately predict thickness of topsoil above the Bt horizon. Variable-rate eN applications based upon soil EC have been compared to conventional singl rate applications on large plots (1992-98) and at field scale (1996-98)for corn production. Each field was unique with the variable-rate N plan resulting in 5 to 20% less total N than the conventional single-rate plan. Generally, production has not been compromised with variable-rate applications of N on claypan soils. Crop use efficiency of N and post- harvest soil inorganic N were measured to determine the potential relative impact these two systems would have on environmental loss of N. Only in one dry year has post-harvest nitrate been significantly associated with soil and landscape properties. These studies have been particularly valuable since they allow for whole-field prediction of unused fertilizer N and allow for estimating potential N loss during the wet winter months.