2022-23 Rapid Ag: Controlled-release nitrogen and split applications to enhance corn production and environmental protection
Fabian Fernandez, Department of Soil, Water, and Climate
- William Lazarus, Department of Applied Economics
Nitrogen (N) fertilization is essential for corn production, but N loss can diminish environmental health and farmers’ profitability. Excessively wet spring conditions resulting from ongoing climate change exacerbate loss potential of early spring N applications in Minnesota. At the same time, urea has become the major N source, which poses concerns. Because of volatilization issues, urea applications are done early so urea can be incorporated into the soil by tillage before planting. Alternatively, inseason application can reduce N loss in wet springs, but driving in wet fields can be logistically impossible. Also, in-season urea applications add cost and need to be incorporated quickly by rain or irrigation to avoid volatilization losses. Irrigating when unnecessary, simply to incorporate fertilizer, results in added cost and increased N loss potential if followed by substantial precipitation. Based on preliminary studies, one way to circumvent these issues is to use controlled release fertilizers, such as polymer-coated urea (PCU), or PCU-urea blends in tandem with application timing management. A multi-disciplinary team of researchers, extension specialists, and stakeholder is assembled to conduct an in-depth evaluation of these alternatives that are sorely needed before University of Minnesota N guidelines, which are widely used by farmers, can be adjusted.
Objectives and Goals
Minnesota corn farmers and their advisors need local information to best manage their risks and take advantage of all the N tools and strategies available at their disposal. University of Minnesota N Best Management Practices (N-BMPs) are extensively used by farmers, crop consultants, and state government agencies. For example, see recent Groundwater Protection Rule www.mda.state.mn.us/nfr.
To ensure N-BMPs are relevant to current environmental and crop production systems, our goals are to
- Evaluate corn response to polymer-coated urea (PCU) and time of application strategies
- Incorporate this information into the N-BMPs
- Increase awareness and adoption of N-BMP’s through extension-education programs.
Our ultimate goal is to improve corn production in Minnesota through greater N use efficiency and profitability that is environmentally responsible. The objectives are to evaluate various urea, PCU, and PCU-urea blends and N application timing strategies in corn production and determine
- The agronomic and economic optimum N rate and grain yield
- N use efficiency and indirectly the potential for N loss to the environment
- Their costbenefit relationship.
- Generate awareness and adoption by end users of the knowledge learned through extension education programs
Irrigated coarse-textured soils are among the most productive acres in Minnesota, but nitrate leaching is a big problem because it reduces the efficiency of expensive N fertilizer and creates groundwater pollution for a large population that depends on that resource. Although N management is very different for fine-textured soils, similar challenges exist in terms of reduced grain yield and profitability because of N loss that negatively impacts the environment, most notably surface waters and the atmosphere. Unfortunately, managing N to minimize losses to the environment is becoming increasingly difficult in Minnesota due to climate change where the springs are becoming wetter. Along with the change in climate, Minnesota farmers are seeing a large shift in N fertilizer sources available in the marketplace. Anhydrous ammonia, which is a superior source of N to minimize N loss from spring applications relative to urea or other commonly used fertilizers, is becoming increasingly scarce due to health and liability issues, infrastructure, and fewer fertilizer dealers offering it as an option. This source has been rapidly replaced by urea.
Because urea is subject to volatilization loss if left on the soil surface, logistically, the best application time is before tillage for seedbed preparation so urea can be incorporated into the soil. However, the potential for N loss through leaching or denitrification is greater earlier in the spring when there is excess precipitation and N and water demands of corn are low. In-season application of urea can be advantageous to minimize the risk of N leaching and denitrification losses. However, because urea cannot be incorporated by tillage at this time, it has to be either incorporated immediately by irrigation or be applied with a urease inhibitor (which adds cost) to slowdown volatilization until a rain event incorporates urea into the soil. Applying irrigation when it is not needed simply to incorporate fertilizer results in added cost and can lead to increased N leaching if followed by substantial rain events. Further, in-season applications can be risky if wet field conditions prevent equipment traffic for timely applications of N and cause yield reduction due to N deficiency. Using PCU, though it is more expensive than urea, can provide logistic and risk management alternatives. The polymer protects urea from loss early in the season and releases N slowly later as the crop N demands increase.
Recent preliminary studies in Minnesota have shown that PCU and in-season applications can be a viable alternative to pre-plant urea. In coarse-textured soils in the central sands region, split application of urea consistently produced more grain than a single pre-plant application, and PCU in preplant applications was superior to pre-plant urea (Spackman, 2018; Lamb et al., 2015). For fine-textured soils, split applications were generally better than single pre-plant applications of urea when springs were wet (Spackman et al., 2019). In fine-textured soils compared to pre-plant urea, pre-plant PCU or a split application (pre-plant PCU plus urea applied at V4 corn growth stage) produced more grain yield and less N leaching and nitrous oxide emissions (Menegaz and Fernández, 2020). While these studies show that PCU and time of application can be viable management alternatives to improve corn production, N use efficiency, and environmental protection, they are limited because they have been conducted as single N rate comparisons and often as secondary objectives in those projects. Minnesota is lacking a comprehensive evaluation of urea, PCU and urea-PCU blends in combination with different application times to determine what strategies are best. Further, given that PCU and split applications often add cost relative to pre-plant urea applications, studies with several N rates that include these N sources and times of application variables are needed to conduct economic analyses and truly evaluate their cost-benefit feasibility for commercial farms.
Over the years, the PI has been discussing these findings with his extension clientele and the Minnesota Department of Agriculture. These individuals and groups (see letters of support) and the need to revise our current N-BMPs in Minnesota are the motivating force behind this proposal. The short-term benefit from achieving the objectives of this proposal will be an update to current University of Minnesota N-BMPs. The long-term effect will be better N management that enhances corn production, profitability, and environmental protection for Minnesota and Minnesotans.
- Lamb, J.A., C.J. Rosen, P.M. Bongard, D.E. Kaiser, F.G. Fernández, and B.L. Barber. 2015. Fertilizing corn grown on irrigated sandy soils. Univ. of Minnesota Extension. AG-NM-1501.
- Menegaz, S.T., and F.G. Fernández. 2020. Nitrogen source and application timing for corn to mitigate leaching and gaseous N losses. In: Proc. of the 50th Annual North Central Extension-Industry Soil Fertility Conference. 18-19 November 2020.
- Spackman, J.A. 2018. Nitrogen fertilizer rate, source, and application timing effects on soil nitrogen and corn yield. Master’s Thesis. University of Minnesota Library.
- Spackman, J.A., F.G. Fernández, J.A. Coulter, D.E. Kaiser, G.D. Paiao. 2019. Soil texture and precipitation influence optimal time of nitrogen fertilization for corn. Agron. J. 111:2018-2030.