Modeling of conservation practices' effects on nutrients and sediment load reduction from commercial cotton fields using APEX

Authors: THAPA, ARJUN - North Carolina A&t State University; ARYAL, NIROJ - North Carolina A&t State University; Reba, Michele; TEAGUE, TINA GRAY - University Of Arkansas; Payne, Geoffrey; PIERI, ANNA - University Of Arkansas

Submitted to: Journal of Agriculture and Food Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2025
Publication Date: 4/9/2025
Citation: Thapa, A., Aryal, N., Reba, M.L., Teague, T., Payne, G.K., Pieri, A. 2025. Modeling effects of conservation practices on nutrients and sediment load reduction and crop production from commercial cotton fields using APEX. Journal of Agriculture and Food Research. 21(101889). https://doi.org/10.1016/j.jafr.2025.101889.
DOI: https://doi.org/10.1016/j.jafr.2025.101889

Interpretive Summary: Farmer often plant cover crops to help protect the soil and reduce pollution from their field. This pollution includes sediment and nutrients that can wash away into rivers or lakes when it rains. To see how much pollution is reduced by cover crops, scientists can measure the water and those pollutants leaving the fields. But doing this every time it rains can be expensive and time-consuming. Instead of measuring every time, scientists can use computer programs to predict how much pollution might flow from the fields. In this project, we used a program called the Agricultural Policy Environmental eXtender (APEX) to predict the amount of sediment and nutrients leaving the fields. The results showed that the program is very accurate at these predictions. This means we can use this program to estimate pollution levels decrease by cover crops instead of taking expensive measurements each time, saving both time and money. Additionally, planting cover crops helps to reduce water pollution from the field, which benefits aquatic organisms, animals that drink that water, and humans.

Technical Abstract: Mapping agricultural pollution sources typically requires extensive monitoring and resources but biophysical models can facilitate pollutant mapping from single or multiple agricultural areas within a watershed and offer a more efficient solution. This study employed the Agricultural Policy Environmental eXtender (APEX) model version 1501 to simulate nutrient and sediment loads, as well as crop yield, from commercial cotton fields under the presence and absence of a filter strip/cover crop treatment. The daily data used for model calibration and validation included total surface runoff, sediment and nutrient loads calculated from surface runoff samples collected at the edge of the 7.8 ha cotton control field during eht study period from 2015 to 2022 in the Lower Mississippi River Basin in Arkansas. Sensitivity analysis, calibration, and validation were preformed using the APEX aut-calibration and uncertainty estimator for the control field. The calibrated model for the control field was applied to the treatment field that had cover crops and filter strips. The model's performance was assessed using R2, Nash-Sutcliffe efficiency (NSE), Percentage bias (PBIAS), and root mean standar deviation ratio (RSR).The analysis demonstrated that the implementation of cover crops and filter strips significantly reduced runoff, sediment, total phosphorus, and total nitrogen loads (p<0.05). The simulation results indicated that the cover crop and filter strip treatment reduced runoff by 41%, sediment load by 58%, total phosphorus (TP) by 63%, and total nitrogen (TN) by 56% compared to the control field. The simulated cotton yield results indicated no significant difference in cotton lint production due to the cover crop and filter strip applications (p>0.05). The results demonstrated that cover crops and filter strips effectively reduce pollutant load while maintaining crop yield, reinforcing their value as sustainable conservation practices.