Agronomic and economic implications of cover crop and phosphorus fertilizer management practices for water quality improvement

Abstract

Phosphorus (P) fertilization practices and winter cover crops are promoted to protect water quality yet can potentially influence crop yield and profitability. This study examined the impacts of three P fertilizer management practices (no P, fall broadcast P, and spring injected P) and winter annual cover crop use on yields, net returns, and water quality in a no‐till corn–soybean rotation. Treatments were replicated in a 4‐yr field study where sediment, total P, and dissolved reactive P (DRP) losses in edge‐of‐field surface runoff were continuously monitored. Production budgets were developed for each treatment and coupled with water quality data to identify optimal practices and opportunity costs for improving water quality. Applying P fertilizers increased crop yield regardless of application method or cover crop, but the response was more pronounced in corn than soybean. The cover crop reduced corn grain yield in 1 yr with high temperature and low precipitation but did not impact grain yield in the other corn year or either year of soybean. The most profitable treatment was fall broadcast P fertilizer with no cover crop, which also had the greatest total P and DRP losses and near greatest sediment loss. The lowest‐cost methods of reducing total P, DRP, and sediment losses were, respectively, no P fertilizer without a cover crop ($47.56 kg−1 total P), spring injected P fertilizer without a cover crop ($56.47 kg−1 DRP), and spring injected P fertilizer with a cover crop ($0.16 kg−1 sediment). Widespread adoption of these practices will likely require monetary incentives.

Cover crops impact phosphorus cycling and environmental efficiency in a corn–soybean system

“…Cover crop biomass was greater in the FB treatment compared to the CN, and the SI treatment produced similar biomass to both the CN and FB treatments (Table 2). Cover crop biomass was significantly different for each year of the study due to variable growing season conditions and year‐to‐year differences in cover crop seeding and planting dates (Nelson et al., 2023). Notably, 2019 had substantially less biomass compared to the other years.…”

“…Details on agronomic management can be found in (Nelson et al., 2023). Briefly, the first cover crop was sown in the fall of 2014 and each year thereafter, following the harvest of the main crop.…”

“…Yield results summarized by Nelson et al (2023) indicate CC treatment decreased yield in 2017, driving the main effect of cover crop to be significant across years, on yield. Additionally, SI significantly increased main crop yield compared to FB only in 2019; in all other years, the FB and SI treatments had a similar effect on main crop yield.…”