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item Bausch, Walter
item Delgado, Jorge

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2005
Publication Date: 12/23/2005
Citation: Bausch, W.C., Delgado, J.A. 2005. Impact of residual soil nitrate on remote sensed plant n status of irrigated corn for managing in-season nitrogen applications. Precision Agriculture. Manuscript number PRAG276-04

Interpretive Summary: Nitrogen (N) fertilizer has received attention for a long time as a potential source of ground water pollution because of the mobility of the nitrate ion through the soil and because of the large amount of N fertilizer used. Farmers may over fertilize and over irrigate their crops to avoid the risk of reducing yield. Since almost all soils within a field vary in the percentage of sand, silt, and clay, some areas in a field may accumulate excess nitrates in the soil profile. Uniform N applications to a crop typically results in over fertilizing areas of a field already high in residual soil nitrates and under fertilizing other areas. This study used remote sensing to assess the plant N status of irrigated corn in two areas of the field that had significant differences in residual soil nitrate-N to determine when the crop should be fertilized. Results showed that the corn crop in the area high in soil nitrates required one in-season N application whereas three in-season N applications were required by corn in the low residual soil nitrate area. The cooperating farmer applied five in-season N applications to the remainder of the field based on his traditional N management practice. Nitrogen savings based on remote sensing of plant N in the high and low residual soil nitrate areas compared to the farmer's management practice were 78% and 52%, respectively, with no reduction in grain yield. Applying N fertilizer based on crop need may improve N management by decreasing N inputs and decreasing the potential for N leaching. Remote sensing can help manage the spatial variability of N sources within a field that are available to a crop during the growing season.

Technical Abstract: Spatial and temporal variability of soil nitrogen (N) supply conjoined with temporal variability of plant N demand makes conventional N management difficult. This study was conducted to determine the impact of residual soil nitrate-N (NO3-N) on ground-based remote sensing management of in-season N fertilizer applications for commercial center-pivot irrigated corn (Zea mays L.) in northeast Colorado. Wedge shaped areas were established to facilitate fertigation with the center pivot in two areas of the field that had significant differences in residual soil NO3-N (P<0.0001). One in-season fertigation (48 kg N ha-1) was required in the Bijou loamy sand (Coarse-loamy, mixed, superactive, mesic Ustic Haplargids) soil (high residual NO3-N) vs. three in-season fertigations totaling 102 kg N ha-1 in the Valentine fine sand (Mixed, mesic Typic Ustipsamments) soil (low residual NO3-N). The farmer applied five fertigations to the field between the wedges for a total in-season N application of 214 kg N ha-1. Nitrogen input was reduced by 78% and 52%, respectively, in these two areas compared to the farmer's traditional practice without reducing corn yields. Our ground-based remote sensing management of in-season applied N increased N use efficiency and significantly reduced residual soil NO3-N (0-1.5 m depth) in the loamy sand soil area (P<0.0001). Applying fertilizer N as needed by the crop and where needed in a field may reduce N inputs compared to traditional farmer accepted practices and improve in-season N management.