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Late nitrogen (N) fertilizer applications in maize: investigating N fluxes at the field and plant scale

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Title: Late nitrogen (N) fertilizer applications in maize: investigating N fluxes at the field and plant scale
Author: Nasielski, Joshua
Department: Department of Plant Agriculture
Program: Plant Agriculture
Advisor: Deen, Bill
Abstract: With the increasing availability of high clearance equipment, there is growing interest in late N management strategies where a certain proportion of fertilizer N is applied much later in the season than is traditionally done. A suite of experiments was conducted to understand the physiologic response of maize to late N applications. A field experiment was conducted to understand how yield formation in maize is affected by late N management strategies. It was found that the bulk of N fertilizer can be delayed until 9-11 days before silking (V13) without any grain yield penalty. Mechanistically, this is because maize yield potential established just after silking is maximized at relatively low initial N rates. Low N rates become suboptimal in terms of yield only after silking. Thus, on soils which supply at least moderate amounts of indigenous N via mineralization, the bulk of fertilizer N can be applied much closer to silking than traditionally done without yield penalty. A greenhouse study found that the accumulation of luxury N prior to silking can help buffer grain yield against N stresses experienced after silking, and also elucidated the mechanisms responsible for this protective effect. To the extent that late N applications reduce luxury N uptake prior to silking, they may cause maize crops to be less resilient to shortfalls in post-silking N availability. Late N applications presumably increase post-silking N uptake due to greater late-season soil N availability relative to N applications made around planting. A greenhouse study was conducted to better understand how exogenous soil N supply and maize N demand interact to regulate post-silking N uptake in maize. Our data supports a model that characterizes post-silking N uptake as a function of plant source-sink ratio, rather than solely a function of grain yield, post-silking biomass accumulation, or soil N supply. After calibrating and validating the Denitirification and Decomposition (DNDC) computer model, the effects of 16 different N management strategies, including late N applications, on the environmental performance of economically optimum N rates (EONR) was assessed. Late N applications reduced leaching N losses at the EONR modestly (~7 kg N ha-1) but did not reduce yield-scaled N losses. It was found that N source and N placement decisions more strongly affect the agronomic and economic performance of the EONR relative to N timing.
Date: 2019-05-07
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