Use of the 4R’s (right rate, right source, right placement, right time) for nitrogen (N) management may improve farmer productivity and enhance environmental sustainability. However, best management practices for the 4R’s are not consistent across landscapes due to variable soil and growing season conditions. Research that systematically modifies the 4R’s may allow for selection of best N management practices for high yielding corn (Zea mays L.) and N use efficiency. Because corn yield is dependent on N uptake from the soil, frequent in-season soil sampling may be useful to assess N availability to the crop over time and may be a useful tool to forecast soil N sufficiency for agronomically optimal grain production. We examined the effect of N rate, source, and time of fertilizer application on soil N availability and corn grain yield for 12 site-years across Minnesota for the 2014 and 2015 growing seasons. Fertilizer treatments consisted of: pre-plant urea applied at 35 to 45 kg N ha-1 increments at seven to eight N rates; pre-plant applications at 105 or 135 kg N ha-1 of anhydrous ammonia with (AAI) and without (AA) nitrification inhibitor, polymer coated urea (PCU), and PCU-urea blends at ratios of 1:2 (PCU-U 1:2) and 2:1 (PCU-U 2:1); and split fertilizer applications of 35 or 45 kg N ha-1 urea ammonium nitrate applied as a starter fertilizer and side-dressed with 70 or 90 kg N ha-1 urea plus nitrification inhibitor at the V2, V4, V6, V8, or V12 vegetative development stage. Site-years were grouped based on similar soil textures and responses of grain yield to either N rate or time of fertilizer application. In-season soil and plant samples were collected five times during the growing season. The modified arcsine-log calibration curve was used to examine the potential of in-season soil nitrate-N, ammonium-N, and total inorganic N concentrations to predict corn grain yields and the in-season N fertilizer rate needed to achieve those yields. Coarse textured soils were prone to rapid N loss for all pre-plant fertilizer treatments where yield was not maximized even when 315 kg N ha-1 urea was applied. AA, AAI, and PCU delayed nitrification or fertilizer N release from the prill relative to pre-plant urea for improved synchrony of N availability to corn demand with a 1.6-fold yield improvement on average. Likewise, split-applications from V4 to V12 improved yields 1.5 to 1.9-fold over pre-plant urea with 50 to 63% of the applied fertilizer N rate recovered in plant biomass. On fine-textured soils, seasonal precipitation strongly influenced site response to N fertilizer treatments. Site-years with low N loss potential had no yield differences between N sources and were either non-responsive to N rate or optimized yield at 180 kg N ha-1. Site-years with high N loss potential had reduced N availability and did not maximize yield regardless of the applied N rate. Under these conditions, yield, N use efficiency, and economic return was greatest for PCU-U blends relative to other N sources. Precipitation timeliness was important for incorporation of split-applied urea and for corn N uptake. With dry summer conditions, fertilizer N accumulated in the 0- to 30-cm soil layer primarily as ammonium-N. Under well-distributed rainfall, side-dressed N was rapidly nitrified and taken up by the crop with the V2 to V8 timings producing 11.2 Mg grain ha-1 on average. This highlights the importance of synchronizing in-season fertilizer applications with precipitation events and that adequate soil moisture is required for soil N to be crop available. The modified arcsine-log calibration curve successfully correlated grain yields with soil test values for fine-textured sites but showed limited utility for coarse textured soils because of excessive N loss. For fine-textured soils, V4 soil nitrate from the 0- to 30-cm was better correlated than pre-plant or V8 timings and was similarly correlated to deeper sampling depths or N species. This is positive as it represents labor and analysis cost savings as well as greater time for side-dress fertilization when the crop is small. With this study, we demonstrated that seasonal weather patterns and soil texture are major drivers of soil N availability such that there is not a single N fertilizer rate, source, or application timing that will optimize yields in all situations. On coarse-textured soils or when early spring conditions are expected to be wetter than normal, pre-plant urea should be avoided in favor of split-applications or other N sources, but little differences are likely between sources or applications timings when N loss potential is low.
University of Minnesota M.S. thesis.May 2018. Major: Land and Atmospheric Science. Advisor: Fabian Fernandez. 1 computer file (PDF); xii, 93 pages.
Nitrogen Fertilizer Rate, Source, And Application Timing Effects On Soil Nitrogen And Corn Yield.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.