A Decision-Support System for Economic Feasibility of Subsurfaced Poultry Litter

Cattle (Bos spp.) producers routinely spread fertilizer or broadcast poultry (Gallus gallus L.) litter to improve forage production. With poultry litter widely available across the southeastern United States and being a cheaper source of plant nutrition than commercial fertilizer when proximal to application sites, the novel application of litter below the soil surface, while costly, allows for greater nutrient retention than broadcasting. Since quantifying costs and benefits of subsurfaced litter is complex, we develop and present a decision support spreadsheet for automated farm-scale model comparisons across modes of nutrient management. We compare subsurfaced litter to commercial fertilizer and broadcast litter in user-specific scenarios involving equipment choices (new, used, custom), desired nutrient needs for crops grown, litter nutrient concentration, and interval between litter application given the slow-release nature of litter compared to commercial fertilizer. Using Visual Basic for Applications programming available with Microsoft Excel®, we develop a decision aid that collects relevant user-specific farm parameters that allow customization of output. Performance data of the innovative subsurface application equipment as observed during field operation and published engineering equipment performance standards, combined with cost information, allow estimation of relative performance metrics. Break-even and sensitivity analyses are performed to identify key equipment modifications or subsidies needed to speed adoption of subsurfacing poultry litter to minimize odor and nutrient runoff externalities experienced with broadcast litter. Results showed that subsurfaced litter can compete with commercial fertilizer on a cost/return basis and especially so in situations where organic farming practices may be targeted. With a longer interval between litter application, enhanced annual capacity utilization of the applicator, and a good match between nutrient needs of crops fertilized and litter nutrient content, the decision aid demonstrated cost savings with subsurfaced litter over commercial fertilizer while being more or less cost-neutral in comparison to broadcast litter. The decision aid lends itself to estimating operation-specific subsidies needed to encourage adoption of subsurface application of litter with the intent to reduce nutrient runoff and odor externalities. Alternatively, the sensitivity analyses pinpointed the need to enhance the performance rate of subsurface application that may be achievable by increasing the implement’s width.