Submitted to: Crop Science Society Of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2003
Publication Date: 12/30/2003
Citation: Bausch, W.C., Delgado, J.A. 2003. Ground-based sensing of plant nitrogen status in irrigated corn to improve nitrogen management. Crop Science Society Of America. Interpretive Summary: Nitrogen (N) use has increased during the past four decades from about 37 % of total nutrient use in 1960 to over 55 % in 1998. This gain in N use is a direct result from increased farmer demand due primarily to favorable crop yield response to N fertilizer. However, corn is often over-fertilized because N fertilizer is less expensive than potential yield loss due to N deficiency. Farmers following conventional practices may apply N fertilizer at rates based on optimistic yields but may not account for all sources of available nutrients. Because of spatial and temporal variability in soil N supply, strategies based on detecting crop N status and meeting crop N requirements with carefully timed N fertilization may ultimately be more successful in improving N use efficiency than strategies that attempt to estimate soil N supply. Ground-based remote sensing was utilized to assess the N status of irrigated corn and to recommend when N applications should be applied. Less N (100 lb/ac) was applied to the test area for two growing seasons compared to traditional N management practiced by the cooperating farmer. Grain yields in the test area relative to an identical area under traditional N management were 1.04 and 1.01 for the two consecutive years. Thus, grain yield was not reduced with reduced N application. Reduced N application equated to $102/ac and $168/ac, respectively, for the first and second years of the study. These numbers indicate potential cost reduction for N with improved methods of N management but do not consider the costs associated with the technique.
Technical Abstract: In-season application of nitrogen (N) to irrigated corn (Zea mays L.) without adequate knowledge of crop N requirements can often result in inefficient use of N. Remote sensing techniques can be used to estimate a crop's N status and improve in-season N management. The objective of this paper was to investigate use of ground-based remote sensing and the N Reflectance Index (NRI) to improve in-season N management of corn in a commercial sprinkler-irrigated field. A wedge shaped area was selected in a sandy, low productivity area of the field. Canopy radiance and solar irradiance measurements in the green and near-infrared portions of the electromagnetic spectrum were periodically acquired from a high-clearance tractor platform during the 2000 and 2001 growing seasons. These data were converted to canopy reflectance to calculate the NRI which was imported to ArcView for further processing. The wedge area was fertigated when the mean value of the NRI became less than 0.95 or more than 50% of the area mapped as N deficient. In-season N applied to the wedge was 102 kg ha-1 for each growing season which was significantly less than the 214 kg N ha-1 applied each season to the rest of the field with farmer traditional practices. This reduction in applied N (112 kg ha-1) equated to an input cost savings (N only) of $41.44 ha-1 in 2000 and $68.32 ha-1 in 2001; cost for data acquisition, data analysis, and data interpretation for recommending fertigation were not considered. Mean grain yields in 2000 for the wedge and a similar sized area of the field within this low productivity zone outside the wedge were 12.5 and 12.0 Mg ha-1, respectively. In 2001, yields were 10.8 and 10.7 Mg ha-1, respectively, for the two areas. Thus, grain yield was not decreased using the "as needed" by the crop concept to time N applications.