Field scale nitrogen load in surface runoff: Impacts of management practices and changing climate

Authors: HOU, CONGYU - University Of Illinois; CHU, MARIA - University Of Illinois; GUZMAN, JORGE - University Of Illinois; ACERO TRIANA, JUAN - University Of Illinois; Moriasi, Daniel; STEINER, JEAN - Retired ARS Employee

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2019
Publication Date: 8/23/2019
Citation: Hou, C., Chu, M.L., Guzman, J., Acero Triana, J.S., Moriasi, D.N., Steiner, J.L. 2019. Field scale nitrogen load in surface runoff: Impacts of management practices and changing climate. Journal of Environmental Management. 249:109327. https://doi.org/10.1016/j.jenvman.2019.109327.
DOI: https://doi.org/10.1016/j.jenvman.2019.109327

Interpretive Summary: The use of nitrogen (N) fertilizer during the 20th century increased crop production significantly to help feed an increasing world population. However, excessive use of N fertilizer in agricultural lands has led to serious water quality problems. The severity of the problem depends on factors such as land management and the prevailing climate. However, in most areas the individual and combined effects of these factors is unknown because of lack of long-term continuous monitoring of N concentration. In this study, we evaluated the impacts of these factors on N load in the Willow Creek sub-watershed in central Oklahoma. The Pesticide Root Zone Model 3 was used to run different crop rotation schemes, fertilizer application schemes, and projected climate scenarios. The model outputs were used to quantify the impacts of these factors on N load. In addition, model scenario outputs were used to compute the probability of occurrence of N loads, classified into high, moderate, and low categories. Results indicated that a projected 17% increase in average annual rainfall increased the maximum monthly N load by 43%. Results further showed that crop rotation practices lowered both the N load and the probability of high N load. Spring fertilizer application reduced N loads in summer and fall but at the risk of increased probability of generating high N load in April and May. Fertilizer application rate affected the amount and the probability of occurrence of high N load most compared with other factors. The results showed that land management practices applied based on the soil N leaching potential reduced maximum monthly N load by 13% and average annual N load by 6%. The approach used in this study can be adopted and applied to quantify the impacts of conservation practices for programs such as the conservation effects assessment project (CEAP).

Technical Abstract: The use of nitrogen (N) fertilizer boosted crop production to accommodate 7 billion people on earth in the 20th century. However, the massive use of N fertilizer in agricultural lands has resulted in serious environmental problems for the soil, surface water, groundwater, and the oceans. Due to the difficulties in continuous field monitoring of surface runoff and N concentration over a long period, the combined effects of different agricultural activities, climate, and soil properties are unknown. The objective of this study was to evaluate the impacts of the combination of factors, management and climate, on runoff linked N load at the field scale level. A framework to analyze changes in N load at a high spatio-temporal resolution under high greenhouse emission climate projections was developed based on PRZM-3 model in the Willow Creek Watershed in the Fort Cobb Experimental Watershed in Oklahoma. Specifically, 12 combinations of factors including different crop rotation schemes, different fertilizer application schemes were evaluated using 32 climate scenarios based on their N load via surface runoff from 2020 to 2070. Moreover, the Potential Nitrogen Load Index (PNLI) was determined to assess the field’s susceptibility to generating N load through surface runoff. Results showed that crop rotation practices lowered both the N load and the probability of high N load. Spring fertilizer application reduced the negative effects in summer and fall but at the risk of increased probability of generating high N load in April and May. Fertilizer application rate was proven the most critical factor that drives both the amount and the probability of occurrence of high N load. To address this issue, customized target management practices were implemented at the field scale where they were most needed. The results showed that by implementing the target application management approach, the monthly N maximum value decreased by 13% and the annual mean N load decreased by 6%. The model framework and analysis developed in this research can be used to analyze the tradeoffs between environmental welfare and economic benefits of N fertilizer.