Agronomy and Horticulture, Department of


First Advisor

Richard B. Ferguson

Date of this Version


Document Type



A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Agronomy, Under the Supervision of Professor Richard B. Ferguson. Lincoln, Nebraska: February, 2019.

Copyright (c) 2019 Leonardo Mendes Bastos


Nitrogen (N) is often the most limiting nutrient to corn. Once applied to the field, N can be lost through different pathways, which contributes to low N use efficiency (NUE) by plants. Increases in NUE and decreases in N losses can be potentially achieved by using management options that allow a better synchrony between N supply and demand, such as stabilized fertilizers, and spatially-variable sensor-derived in-season N application. Three studies were conducted in order to assess the effects of different stabilized fertilizers and crop canopy sensors on irrigated corn yield. The first study evaluated the effect of urease inhibitor on ammonia losses and corn grain yield. The use of urease inhibitors significantly reduced ammonia volatilization losses by 21 to 62%, but this did not translate into higher corn yields. The second study evaluated the effect of various management practices along with the use of a nitrification inhibitor and their interaction with weather on irrigated corn grain yield over 28 yrs. The use of a nitrification inhibitor had negative, neutral, and positive effects on corn grain yield, and the magnitude of its effect was less than other management practices. The most important weather variables in explaining different yield responses were year- yield potential, precipitation volume and distribution, and air temperature. The third study compared active and passive crop canopy sensors in assessing corn N deficiency and the accuracy of recommended side-dress N rates compared to the economic optimum N rate. This study included eight field studies using different N fertilizer rates and the use of both active and passive crop canopy sensor during the mid-vegetative growth stage in corn. Active and passive sensors recommended comparable side- dress N rates given proper selection of algorithm inputs. Their recommendation was partially or fully accurate in four of six studies. Both stabilized fertilizers and crop canopy sensors are important management tool options for producers, and an understanding of their strengths and weaknesses is needed to guide proper adoption decisions.

Advisor: Richard B. Ferguson