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.)

Abstract

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 m2) 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 ( 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.