Adapting Nitrogen Management to Climate Change: Evidence from Field Experiments in Iowa

Abstract

We assess how the effect of nitrogen management on corn production and water pollution is impacted by abnormally high precipitation using random field experiments. Efficient management of nitrogen fertilizer has been of public interest because leached nitrate contaminates drinking water sources and creates nutrient pollution in lakes and the ocean. We question a prevailing belief that more nitrogen fertilizer is needed against high precipitation to ensure production. First, our model shows that uncertainty about the impact of rainfall on the productivity of nitrogen fertilizer leads farmers to apply more under this belief. However, our empirical test exploiting a random experiment shows that nitrogen fertilizer is less needed at the optimum, resulting in higher corn outputs under abnormally heavy rainfall than the normal weather because of increased productivity. Based on the experiments implemented by Iowa Soybean Association in Iowa during 2006-2014 and 2017-2021, heavy rainfall is usually a good weather condition rather than destructive in our sample. Next, we propose to use a corn stalk nitrate test (CSNT) as a proxy of nitrogen leaching at the farm level, which is perceived as unmeasurable at a non-point source. We show that the likelihood of leaching increases under abnormally heavy rainfall than the normal weather. Yet, our results suggest farmers can improve fields’ adaptive capacity by adopting more resilient practices such as side-dressing. This study contributes to understanding abnormal weather’s effect on environmental damage at the micro data level.