Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2021
Publication Date: 3/5/2021
Citation: White, K.E., Cavigelli, M.A., Bagley, G. 2021. Legumes and nutrient management improve phosphorus and potassium balances in long-term crop rotations. Agronomy Journal. https://doi.org/10.1002/agj2.20651.
Interpretive Summary: Balancing nutrient inputs and outputs is a fundamental goal of agricultural sustainability, which can be difficult to achieve for farmers who rely on poultry litter to supply nitrogen for crops. To assess system sustainability, USDA-ARS scientists used 13 years of data to compare the balance between inputs and exports of phosphorus and potassium in poultry litter-amended organic and mineral-fertilized conventional crop rotations at the Farming Systems Project in Beltsville, Maryland. Results show that including legume cover crops or forages and increasing crop rotation length/complexity improved phosphorus and potassium balances in organic systems by reducing poultry litter needs and increasing nutrient export, and that conservative phosphorus applications in conventional systems reduced high phosphorus soils while maintaining crop yields. These results will be of interest to organic and conventional farmers, nutrient management specialists, and state and federal employees engaged in nutrient management policies.
Technical Abstract: In grain cropping systems reliant on poultry litter (PL) for nitrogen (N), particularly organic systems, balancing phosphorus (P) and potassium (K) inputs with crop exports is challenging. We used 13 years of data to compare P and K balances of PL-amended organic and mineral-fertilized conventional systems to assess system sustainability. In organic systems, cover crop performance strongly influenced P balances: poorer legume cover crop establishment and biomass production following soybean (Glycine max (L.) Merr.) in a corn (Zea mays L.)-soybean rotation (Org2) led to 58% greater PL application rates to meet corn N needs than in a corn-soybean-wheat (Triticum aestivum L.) rotation (Org3) and a corn-soybean-wheat-alfalfa (Medicago sativa L.) rotation (Org6). Greater P inputs and reduced harvest exports in Org2 and Org3 increased the P balance compared to Org6, resulting in ‘excessive’ soil P. Phosphorus exported in alfalfa in Org6 accounted for 62% of P applied throughout the rotation, resulting in only a small annual P surplus (9 kg P ha-1) and ‘optimum’ soil P. Conservative mineral fertilizer application in conventional systems (one tilled, one no-till) with initially high soil P led to a -124 kg ha-1 P balance and ‘optimum’ soil P. Fertilizer and PL K applications exceeding crop uptake led to positive K balances in all systems but there was greater retention of PL than fertilizer K. Legume cover crops or forages and increasing crop rotation length/complexity improved organic system P and K balances, and conservative P applications in conventional systems reduced high soil P while maintaining yields.