Plant available nitrogen varies with crop rotation due to legacy effects of legume and poultry litter inputs

Authors: White, Kathryn; Cavigelli, Michel; Schomberg, Harry; Mirsky, Steven

Submitted to: Agriculture, Ecosystems & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2026
Publication Date: 1/16/2026
Citation: White, K.E., Cavigelli, M.A., Schomberg, H.H., Mirsky, S.B. 2026. Plant available nitrogen varies with crop rotation due to legacy effects of legume and poultry litter inputs. Agriculture, Ecosystems & Environment. 400. Article e110239. https://doi.org/10.1016/j.agee.2026.110239.
DOI: https://doi.org/10.1016/j.agee.2026.110239

Interpretive Summary: Farmers in poultry producing regions often rely on poultry litter as a fertilizer, sometimes in combination with legume cover crops or forages, to supply nitrogen to their corn crops. However, like conventional fertilizer, poultry litter costs money. Scientists at the USDA-ARS Beltsville Agricultural Research Center in Beltsville, MD quantified the effect of reducing recommended poultry litter application rates in three long-term organically managed crop rotations in the Farming Systems Project. The increases in soil plant available nitrogen seen following long term poultry litter and legume use increased with crop rotation length. Corn did not require any additional nitrogen fertilization in a six-year crop rotation that included three years of perennial alfalfa. In contrast, eliminating poultry litter applications in a two-year corn-soybean and a three-year corn-soybean-wheat rotation reduced yields, but poultry litter applications could be lowered by 43 to 58% without impacting yield. However, weed competition for nitrogen in the two-year rotation reduced yields regardless of application rate. The results of this study indicate that reducing poultry litter recommendations following long-term poultry litter application in crop rotations that include legume cover crops or forages would reduce fertility costs for farmers and lower the risk of nitrogen loss. These results will be used by farmers and their advisers to fine-tune poultry litter application rates and increase farm return on investment.

Technical Abstract: Poultry litter (PL) is used by grain farmers in poultry producing regions to supply nitrogen (N). Knowledge of the effects of long-term applications on plant available N (PAN) is limited, particularly when combined with historical inputs from legume cover crops and forages. Previous research at the Farming Systems Project (FSP) in Maryland, USA found that historical inputs from legumes and PL increased PAN, likely reducing maize PL requirements. We quantified the effects of three reduced PL application rates on PAN and the effects of PAN and weeds on maize yields in three organically managed rotations at FSP. We established PL application rate microplots in two-year hairy vetch (Vicia villosa Roth) plus rye (Secale cereale L.) cover crop–maize (Zea mays L.)–rye cover crop–soybean (Glycine max L.), three-year hairy vetch plus rye–maize-rye cover crop–soybean–wheat (Triticum aestivum L.), and six-year maize–rye cover crop–soybean–wheat–alfalfa (Medicago sativa L.)–alfalfa–alfalfa rotations. Rotational diversity increased microbially active carbon, N, and PAN concentrations, eliminating maize PL requirements in the six-year rotation. In the two- and three-year rotations, eliminating PL decreased yields by 1645 and 1009 kg/ha, respectively. However, application rates could be reduced by 43 % and 58 % without affecting maize yields. Weeds reduced yields in the two-year rotation by 1394 kg/ha. Results indicate that long-term PL and legume inputs increase N storage, N cycling, and soil PAN sufficient to support maize yields, but rates are rotation-dependent. Reducing PL recommendations in comparable rotations, whether organic or conventional, would reduce fertility costs and likely lower N loss risks.