Evaluating Nitrogen Stress and Yield Impacts from Variable-Rate Nitrogen Applications for Potatoes.

The expansion of intensive, irrigated agriculture in Central Minnesota has led to concerns regarding potential increases in non-point source pollution to surficial aquifers. With a goal to improve drinking water quality in this region, which is commonly impaired by nitrate-N, renewed interest has been placed on the role of nitrogen (N) best management practice to meet environmental and agronomic goals. Variable-rate N applications based on multi-spectral remote sensing is a promising management strategy to meet these goals. This study was carried out in 2016 on Russet Burbank potatoes grown on an irrigated, coarse-textured soil in central Minnesota. A total of six N-treatments were imposed including (1)  45 kg N/ha control treatment, (2)  split-applied urea treatments of 180 kg N/ha, (3) and of 270 kg N/ha, (4)  controlled-release polymer coated urea (PCU) treatments of 180 kg N/ha, (5) and of 270 kg N/ha, (6) and split-applied urea applied at a variable-rate. Remote sensing of crop nitrogen stress was conducted weekly using a CROPSCAN Multispectral Radiometer (MSR-16R), and calculated using a Nitrogen Sufficiency Index (NSI) utilizing the MERIS Terrestrial Chlorophyll Index (MTCI) among other indices, with N-treatment (5) serving as the well-fertilized reference. Data on crop N stress were also collected using a SPAD chlorophyll meter. Variable-rate N was applied to N-treatment (6) when the NSI was less than 0.95 in the form UAN through simulated fertigation. Overall, the variable-rate treatment (6) received a total of 247 kg N/ha, which is 22 kg N/ha less than the comparable split-applied urea treatment (4). Comparisons between yield data and N treatment from the first-year of this two-year experiment will be presented.