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Water and Nitrogen Interactions in Maize Production
Water and nitrogen are most often studied separately in academia and managed separately in maize production. However, considering the interactions between the two crop inputs is essential for accurate scientific understanding and beneficial for farm profitability and environmental stewardship. This dissertation explored three of the many opportunities at the intersection of water and nitrogen. The first opportunity was variable rate fertigation. This practice is the intentional application of varying fertilizer rates within a field by first injecting fertilizer into irrigation water and then customizing the water depth and/or fertilizer concentration received at different parts of that field. In chapter 1, mathematical equations were presented to describe various mechanisms of variable rate fertigation via center pivots, and a system of commercial off-the-shelf equipment was shown to be capable of performing variable rate fertigation. The second opportunity was post-season evaluation of grower irrigation and fertilizer nitrogen amounts and timing. In chapter 2, new indices of yield versus inputs were developed to reward optimal seasonal amounts of irrigation and/or fertilizer nitrogen while minimizing the need for intensive measurements. On the other hand, to assess temporal distribution of inputs amid cultivar differences in yield potential, grower season-to-date input amounts were recommended to be compared daily against an optimal range bounded by a pair of dynamic upper and lower thresholds. The third opportunity was removal of water effects on optical canopy measurements that are used to quantify nitrogen sufficiency of corn during the late vegetative and early reproductive growth stages. In chapter 3, the direction and magnitude of water effects were found to be complex results of weather, crop management, and the selected sensor-index combination. Because none of the sensor-index combinations investigated were completely immune to water effects, a new method was proposed to reduce water effects by introducing a proxy variable that indicated the typical water sufficiency of each location relative to the rest of the field. It is the author's sincere hope that the concepts, equations, and methods advanced by this dissertation will be tested, refined, and ultimately applied to improve on-farm irrigation and nitrogen management in west central Nebraska and beyond.
Agronomy|Agricultural engineering|Water Resource Management
Lo, Tsz Him, "Water and Nitrogen Interactions in Maize Production" (2018). ETD collection for University of Nebraska - Lincoln. AAI10982734.