Effect of treating field spatial variability in winter wheat (Triticum aestivum L.) at different resolutions, and adjusting midseason nitrogen rate using a sensor-based optimization algorithm to improve use efficiency in corn (Zea mays l.)

Scope and method of study. For chapter one, resolution trials were conducted to determine the scale at which spatial variability in winter wheat should be treated using an in-season nitrogen fertilization optimization algorithm (NFOA). The treatments included variable N rate applications at three resolutions (0.84, 13.37, and 26.76 m2), a fixed N rate at 90 kg ha-1 applied preplant and midseason, and a check plot arranged in a completely randomized design with three replications. For chapter two, experiments were conducted to formulate an in-season NFOA to estimate midseason N rates that maximize corn growth and minimize inputs, and to determine the optimum resolution to treat spatial variability in corn. The experiment consisted of 13 treatments arranged in a randomized block design with three replications. Treatments included: a 134 kg N ha-1 fixed rate applied in split, preplant- and sidedress-only; a 67 kg N ha -1 fixed rate applied preplant- and sidedress-only; three NFOA-based midseason N rates (RICV-, RI- and flat-RICV-NFOA) with (67 kg N ha -1) and without preplant N; and two resolutions (0.34 and 2.32 m 2) tested for RICV-NFOA only.; Findings and conclusions. For chapter one, the NFOA-based N rates achieved a higher N use efficiency (NUE) value of 41% compared with 33% of the 90 kg N ha-1 fixed rate applied midseason. Treating spatial variability using NFOA at 13.4 m2 achieved the highest NUE value of 56%. Four out of six site years resulted in a higher net return ({dollar} 5 to 101 ha-1) when an NFOA approach was used. Treating spatial variability at 13.4 m2 using the NFOA resulted in increased NUE and net return. For chapter two, with 67 kg N ha-1 preplant application, midseason RI-NFOA-based N rates improved NUE to 64% when compared with 56% of the134 kg N ha-1 fixed rate split applied. The RI-NFOA midseason N rates resulted in higher grain yield and net return in three of six high yielding site years. In general, the use of midseason N rate recommendations based on N demand of predicted yield potential resulted in improved NUE and net return compared with fixed N fertilizer application at 134 kg N ha-1.