Effect of irrigation on fertilizer nitrogen requirement, economic returns, and water availability in a corn-soybean rotation
Abstract
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT REQUEST OF AUTHOR.] In regions of the US and the world where precipitation does not consistently meet crop water needs, there is extensive research documenting the value of irrigation to increased and/or stabilized yields. Delaying nitrogen (N) applications into the growing season supports more accurate N recommendations and reduces potential for N loss; but delayed applications can pose risks including lower yield. The objectives of this study were to: 1) Evaluate effect of irrigation strategy on yield potential and economic returns in a corn-soybean rotation on a claypan soil; 2) Evaluate an ET checkbook method for assessing water status of corn and soybeans under two irrigation methods; 3) Understand how delayed N applications affected the economically optimum N rate (EONR) and the yield potential of corn, as affected by irrigation; and 4) Evaluate the effect of irrigation strategy on resilience of maximum corn yield to timing of nitrogen application. Two irrigation experiments were conducted at UNIVERSITY OF MISSOURI SYSTEM Greenley Research Center near Novelty, MO from 2015 to 2018. In each experiment, three irrigation treatments: sprinkler irrigation, subsurface drip irrigation, and no-irrigation control were set up in a randomized block design with three replications. One set of plots was planted to corn and other to soybean. Both were managed as a corn-soybean rotation resulting in both phases of the rotation present in each year. Optimum fertilizer N rate was determined at V-6 and V-10 by applying six N rates (0, 61, 135, 202, 270, and 337 kg N ha-1) as a split-plot treatment within irrigation plots. Additionally, we tested yield effects of 270 kg N ha-1 applied preplant, V-6, V-10, VT and R3, comparing the N applied as a split application (40% preplant as anhydrous ammonia) or all at the designated time. All N except the preplant split treatment was surface applied as ammonium nitrate. Using sensors to schedule irrigation likely would have resulted in better estimate water deficit than the ET checkbook method in corn-soybean rotation on a claypan soil. Sprinkler irrigation attained higher yields with less N than drip irrigation. There was no economic benefit to irrigation in the three-year study due to limited or no response to irrigation in 2016 and 2017 and yield loss in corn due to under-irrigation using the checkbook method in 2018. There was no effect of application timing on EONR in any of the irrigation treatments. Delaying N application past V-10 required split-applications to avoid yield loss. This research documented substantial flexibility in timing of N applications and that higher changes in yield potential largely explained higher N requirements in irrigated corn.
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Ph. D.
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