Nutrient management dynamics in Northwest Minnesota corn production

Lindsay Pease

Recent increases in corn production in Northwest Minnesota (NW MN) means that additional soil fertility information is needed to ensure that recommendations are accurate for the soil in this region. The overall goal of this project was to evaluate how nutrient management decisions impact nitrogen (N) and phosphorus (P) dynamics in Northwest Minnesota soils. To meet this goal, we conducted a two-year field trial and a complementary laboratory experiment to evaluate the potential agronomic benefits and environmental tradeoffs of three different P fertilizer sources (MAP, MESZ, struvite), and three rates of P fertilizer (single rate, double rate, none) ahead of corn in a corn-soybean rotation. Field trials demonstrated that phosphorus rate and proper soil fertility management were more important than P fertilizer source when managing corn ahead of soybeans. We saw some evidence that MESZ improved zinc uptake at higher P levels, but this did not translate to greater harvested yields. Factors outside of soil fertility likely affected corn yields in 2022 and 2023. We observed dry soil conditions and net nitrogen immobilization in the soil, particularly during the early growing season. Although sufficient N was present in the soil, it was not necessarily in a form that the crop could use. Our laboratory analysis simulating flooded soil conditions showed that it took approximately three weeks to see dissolved P release from soil to water.

Based on our findings, we recommend that Northwest Minnesota farmers continue to follow University of Minnesota’s current fertility guidelines. The current guidelines appear to provide sufficient fertility given that enough moisture is present in the soil to support the corn crop. Double rates provided little agronomic benefit over single rates during the corn phase. We recommend that Minnesota farmers avoid applying double rates of P fertilizer on fields that experience prolonged spring flooding. For these fields, the limited agronomic benefit gained by applying a double rate of fertilizer is unlikely to outweigh increased risk of P loss to surface water.