Evaluating Corn Response to Late-season N Application in Conventional Tillage and No-tillage Systems

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Nitrogen fertilizer applications to corn are typically made early in the season to supply adequate N for rapid growth between the five-leaf stage and silking. However, applying a large dose of N early in the season can lead to losses prior to crop uptake. Moreover, much of the N applied early-season is depleted by the time corn enters reproductive growth. As a result, the crop is entirely reliant on soil N mineralization for the ~70 lb N/acre taken up during pollination and grain fill. Recent evidence suggests that newer hybrids take up more N from the soil post-silking than older hybrids, suggesting that a late application of N fertilizer may be necessary to exploit the full yield potential of modern varieties. Previous studies have shown that delaying the major N fertilizer application to late-vegetative growth stages can decrease yield due to early-season N stress. However, research conducted in Indiana indicates that applying all but 40 lb N/acre early and the remaining 40 lb N/acre at the V12 growth stage can increase crop N accumulation and N recovery efficiency. Nitrogen mineralized from soil organic matter often makes up half or more of total corn N uptake, and it is the primary source of mineral N available for crop uptake during reproductive growth. Long-term no-tillage management generally increases total N stocks and mineralizable N. For example, a long-term tillage comparison study in Kentucky has shown that, relative to conventional tillage, no-till leads to greater soil N concentrations and corn yields when zero N is applied. We hypothesize that a late split application of fertilizer N (V3/V12 growth stages) will result in greater N uptake, yield, and N recovery efficiency than a single early application (V3 growth stage) at the same rate, but the effect will depend on the tillage system. In long-term conventional tillage, the late-split application will exhibit a greater advantage than in no-till due to lower rates of N mineralization during reproductive growth stages in conventional tillage systems. The long-term tillage x N rate trial at University of Kentucky’s Spindletop Research Farm includes two tillage treatments (no-till vs. conventional tillage) crossed with four N rates (0, 75, 150, 300 lb N/acre). Corn is grown every year with cereal rye as a cover crop. We propose to split the plots within this long-term study into two timing treatments: a single N application at the V3 growth stage, and a split-application with 50 lb N/acre applied at the V12 growth stage and the remaining applied at the V3 growth stage. In addition to crop yield, we plan to measure corn N uptake at silking and maturity to quantify how much N is taken up from the soil and how much is remobilized from vegetative biomass after silking. We will also study the impact of tillage system on the rate of soil N mineralization to understand mechanisms underlying the crop response. Lastly, we will test the performance of two in-season tools that may be used to predict crop response to late-season application: leaf chlorophyll content using a SPAD meter and the pre-sidedress nitrate test. Through this research, we aim to provide corn growers with data and tools to support practical decisions on late-season N applications
Effective start/end date2/1/1912/1/19


  • Kentucky Corn Growers Association: $8,000.00


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