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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Sustainable Agricultural Systems Laboratory » Research » Publications at this Location » Publication #352581
Title: Cover crops reduce nitrate leaching in agroecosystems: A global meta-analysis

Author
item THAPA, RESHAM - University Of Maryland
item Mirsky, Steven
item TULLY, KATE - University Of Maryland

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2018
Publication Date: 10/11/2018
Citation: Thapa, R., Mirsky, S.B., Tully, K. 2018. Cover crops reduce nitrate leaching in agroecosystems: A global meta-analysis. Journal of Environmental Quality. 47:1400-1411.

Interpretive Summary: Nitrogen (N) is an essential nutrient to ensure optimal crop yields and is applied based on forecasted yield potential of a given field/location. However, climate is unpredictable and can affect crop yields where irrigation is not available. When the targeted yield goal is not achieved, applied N is not all used by the main crop. Excess N left in the soil after main crop harvest is susceptible to leaching loss and can increase nitrate (NO3-) concentrations in water bodies. Increased NO3-levels in water bodies can cause eutrophication (algal bloom) and degrades aquatic habitats in the Chesapeake Bay. To reduce NO3-loads into the Bay, cover crop adoption is encouraged. We performed a quantitate review of the available literature to understand how well cover crops reduce NO3-leaching from agroecosystems. Compared to the no cover crop control, cover crops reduced NO3-leaching by 56%. We further observed that the effectiveness of cover crops in reducing NO3-leaching varied across sites and years depending on soil type, cover crop planting date, shoot biomass, and climate. Cover crops were more effective in reducing NO3-leaching in coarse-textured soils than in fine-textured soils. Early planting of cover crops in the fall and high shoot biomass in the spring further increased their effectiveness in reducing NO3-leaching. The ability of cover crops to reduce NO3-leaching also increased with decrease in precipitation, suggesting greater effectiveness in years with low precipitation. Overall, our findings indicate that cover crops are an effective way to reduce NO3-leaching and should be integrated into existing cropping systems for water quality benefits. This work will help farmers, researchers, and policy-makers to make cover crop management decisions to minimize agricultures' impact on water quality.

Technical Abstract: Cover crops have been well-recognized as a tool to reduce nitrate (NO3-) leaching from agroecosystems. However, their effectiveness varies from site-to-site and year-to-year depending on soil, cash and cover crop management, and climate factors. We conducted a meta-analysis using 238 observations from 28 studies to: (a) assess the overall effect of cover crops on NO3-leaching, subsequent crop yields, and yield-scaled NO3-leaching and (b) examine how soil, cash and cover crop management, and climate impact the effect of non-leguminous cover crops on NO3-leaching. Compared to no cover crop control, non-leguminous cover crops consistently reduced NO3-leaching by 56% and yield-scaled NO3-leaching by 48%, but had no effect on subsequent crop yields. On the other hand, leguminous cover crops, once terminated, can increase the risk of NO3-leaching in the spring. Among the factors investigated, we identified soil texture, cover crop planting dates, shoot biomass, and relative precipitation as potential drivers for the observed variability in non-leguminous cover crops effectiveness in reducing NO3-leaching. We found evidence indicating greater reduction in NO3-leaching with non-leguminous cover crops on coarse-textured soils and during years of low precipitation (< 90% of the long-term normal). Earlier fall planting and high overall non-leguminous cover crop biomass further reduced NO3-leaching. Overall, our findings indicate that non-leguminous cover crops are an effective way to reduce NO3-leaching and should be integrated into existing cropping systems for water quality benefits.