Location: Soil and Water Management Research
Project Number: 5062-12000-008-18-R
Project Type: Reimbursable
Start Date: Apr 24, 2014
End Date: Apr 30, 2017
1. To determine in field studies if co-application of urease and nitrification inhibitors (UI/NIs) with post-plant fertilizer applications can increase yields at the same level of N input and/or maintain yields at a lower rate of N input compared to single pre-plant N application or compared to split applications without co-application of UI/NIs. 2. To determine in field studies if co-application of UI/NIs with split applications of post-plant fertilizer applications can reduce nitrate leaching potential and N2O compared to single pre-plant N application or compared to split applications w/co-application of UI/NIs. 3. To quantify in lab studies the effect of N addition rate, moisture and temperature conditions, soil carbon availability, and the addition of UIs and NIs on short-term mineralization and nitrification dynamics leading to gaseous and leaching N losses.
A 2-y experiment will be conducted at the University of Minnesota Research Station in St. Paul in fields used for corn production on a Waukegan silt loam. Each year we will establish replicated plots (n=4) comparing the following six management practices: 1. zero-N control (for calculation of N use efficiency and fertilizer induced N losses) 2. single pre-plant application of urea (total N applied = 130 lb/acre) 3. 3 split N applications of urea (total N applied = 130 lb/acre) 4. 3 split N applications of urea (total N applied = 110 lb/acre) 5. 3 split N applications of urea plus UI/NI (total N applied = 130 lb/acre) 6. 3 split N applications of urea plus UI/NI (total N applied = 110 lb/acre) Over the course of the growing season we will make weekly measurements of soil nitrate concentrations to the 30-cm depth. The time-weighted sum of nitrate concentrations (also referred to as nitrate intensity) will be used to represent nitrate leaching potential. In the first few days after each N application, we will also measure soil nitrite concentrations. Soil nitrite is ordinarily overlooked but was shown in a recent study to be critical in explaining N losses from fertilized corn (Maharjan & Venterea, 2013). Emissions of N2O gas will be measured using chamber methods (Venterea et al. 2011b). Measurements will be made once per week starting approximately Apr 1 until planting, then twice per week following planting through Sep 1, and then once per week until Nov 1, for a total of approximately 35 sampling events per growing season. Soil temperature and moisture will be measured during each N2O measurement. The total amount of N2O emitted during the growing season will be estimated by integrating the results from each sampling event. Once the corn has reached physiological maturity, samples of grain and stover will be collected from each treatment to determine yield of grain, stover, and above-ground N yield in both grain and stover. Nitrogen fertilizer recovery efficiency (NFRE) will be determined by subtracting the total grain plus stover N yield in the zero N control from the N yield in each treatment and then dividing by the N application rate. We will also conduct a series of lab incubation experiments using 3 different soils used for corn production in Minnesota and representing a range of conditions with respect to soil texture, organic carbon, pH, and drainage characteristics. The 3 soils will be collected from the Becker Sand Plains Research Farm (excessively drained loamy sand), the Rosemount station (well-drained silt loam), and the Lamberton station (poorly drained loam). With each soil, we will measure short-term biochemical responses to N addition including changes in pH, mineralization and nitrification rates, nitrite and nitrate concentration and N2O production under different moisture, temperature, and carbon conditions expected for a range of field conditions representative of different periods of the growing season from early spring to mid-season corresponding with the periods of N application in the field study. These experiments will be conducted in parallel with the field study over the course of two growing seasons.