The effects of varying nitrogen fertilizer rates and urease inhibitor on soil nutrients, yields, and profits in southeastern Minnesota cornfields

Background/Question/Methods

Nitrogen fertilizer is critical to intensive agriculture and crop growth, yet only 30-50% of nitrogen applied to agricultural land is taken up by crops and most excess nitrogen is unaccounted for at the end of the growing season. This poor management of nitrogen contributes to severe environmental pollution, as well as significant profit loss for farmers. Efficient nitrogen management should be both environmentally and economically sustainable. This research evaluated the effectiveness of two strategies for improving nitrogen management within corn production: 1) the application of nitrogen fertilizer at a fine-tuned, or optimum, rate and 2) the application of a urease inhibitor (ContaiN by AgXplore), which is supposed to stabilize nitrogen in the soil by slowing the initial degradation of urea to ammonia—which is subject to volatilization. We examined the extent to which various fertilizer rates and a urease inhibitor influenced nutrient availability in the soil, nutrient uptake and crop growth, and profitability on two agricultural fields. We collected data pertaining to physical soil properties (soil moisture, organic matter, bulk density), soil nutrient concentrations (nitrate and ammonia), stalk nitrate concentrations, yields and profits. 

Results/Conclusions

Soil nitrate (NO₃-N) concentrations increased significantly in fertilizer treatments with higher rates of urea anhydrous ammonia applied (p=0.028), demonstrating how excessive fertilizer application is linked to nitrogen pollution in the form of leaching or runoff. The application of ContaiN increased ammonium (NH₄⁺) concentrations at shallow depths (p=0.021), suggesting that less nitrogen was initially lost via volatilization following the application of the fertilizer with inhibitor. Increased nutrient uptake and elevated profits associated with the use of ContaiN were only seen when fertilizer was applied at 146 kg N/ha (130 lbs N/acre). Overall, stalk nitrates, yields and profits did not vary significantly across fertilizer treatments or with the use of the urease inhibitor (p>0.05). Results suggested that 1) the effectiveness and profitability of the urease inhibitor may be linked to the rate at which fertilizer is applied, and 2) limiting fertilizer application is likely the most simple, yet effective, way to improve nitrogen management in a profitable way.