Citation:

Yuan, Y., B. Kamrath, AND W. Liu. Effectiveness of Nutrient Management for Reducing Nutrient Losses from Agricultural Fields. Water Research Webinar, Durham (virtual), NC, February 28, 2024.

Impact/Purpose:

Water bodies and coastal areas around the world are threatened by excessive amounts of nitrogen (N) and phosphorous (P) from upstream watersheds, which can cause rapid proliferation of algae. These algal blooms negatively impact drinking water sources, aquatic species, and recreational services of water bodies by producing toxins, also called harmful algal blooms (HABs). Finding ways reducing nutrient losses from agricultural fields is paramount important for EPA program offices and regional partners to make informed decisions to better control nutrient losses from agricultural fields.

Description:

Nutrient export from agricultural areas has been an environmental concern. Nutrient management practices have been studied/implemented to reduce nutrient losses from agricultural fields. Nutrients are managed based on the 4Rs of nutrient stewardship: apply the right nutrient source, with the right rate, at the right time, in the right place (NRCS code 590). There are many challenges in evaluating the effectiveness of nutrient management practices for water quality improvements due to complex processes and mechanisms in nutrient cycling, as well as many other factors in tandem such as other agricultural conservation practices (e.g. residue and tillage management). This presentation includes two investigations performed by ORD scientists: one investigation focused on nitrogen (N) and the second investigation focused on phosphorous (P). Nutrient management for N has been intensively investigated, with research largely focused on crop yields and water quality. Here, authors focused on data extracted from peer-reviewed publications on subsurface-drained agricultural fields in the Midwest U.S. with corn yield and drainage nitrate-N (NO3-N). Nutrient management for P, however, hasn’t been intensively investigated compared to N. Authors therefore focused here on dissolved reactive P (DRP) observations from both plot studies and field-scale studies due to limited availability of P from field studies. Results from the synthesis of N management showed that N fertilizer rate was strongly positively correlated with corn yields, NO3-N loads, and flow-weighted [NO3-N]. Reducing N fertilizer rates can effectively mitigate NO3-N losses from agricultural fields. However, DRP loss was not always positively correlated with P fertilizer application rate. In terms of the fertilizer sources, organic fertilizers significantly boosted corn yields and NO3-N losses compared to inorganic fertilizers at comparable rates. Accurate quantification of plant-available N in organic fertilizers is, however, necessary to guide appropriate nutrient management plans because the nutrient content in organic fertilizers may be highly variable. Results from P management showed that mean DRP concentrations were similar between inorganic and organic fertilizers. No significant differences were found for NO3-N export in drainage discharge among fertilizer application methods. However, subsurface placement reduced mean DRP concentrations significantly relative to surface placement (i.e., broadcasting). Lastly, impact of fertilization timing on NO3-N export varied depending on other factors such as fertilizer rate, source, and weather. Not enough information was found to investigate P fertilization timing on DRP loss.These results suggest that further efforts are required to produce effective local nutrient management plans. Furthermore, government agencies such as USDA-NRCS and USEPA need to work together to address the potential economic losses due to implementation of lower fertilizer rates to achieve improved water quality.

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