A framework for estimating manure nitrogen balance and recycling potential for current and future conditions in the USA

Manure recycling can ameliorate pollution and fertilizer demand, but varying assumptions about recoverable manure nutrients and crop requirements complicate understanding of manure recycling potential. Using nitrogen (N) in the contiguous USA as a case study, we applied methods from six studies to compare manure N balance estimates (recoverable manure minus crop demand). We then developed a framework to assess both current and future potentials of manure recycling. The current balance in the USA is −13.3 ± 1.1 TgN yr−1, reflecting large crop demand currently met with synthetic fertilizer. Improved adoption of current manure management technologies could decrease this deficit by 5%, while future technologies could enable another 21% reduction. However, new manure N application should be reduced by 33–36% to avoid phosphorous (P) overapplication. Improved crop N efficiency could decrease the deficit by 27%. Applying this framework at county level demonstrates variable regional opportunities to improve manure recycling. An assessment framework is developed and applied to the USA, quantifying low rates of current manure recycling and showing that improved manure management and technological development could supply crops with nitrogen equivalent to as much as a quarter of current synthetic N fertilizer use.