Economic and GHG emissions changes of aeration and gypsum application

Abstract

Alternative pasture management strategies are needed to ensure long-term ecological and economical use of abundantly available poultry litter as a source of valuable nitrogen (N), phosphorus (P) and potassium (K). In combination with the common practice of broadcasting poultry litter and soil compaction from equipment and livestock traffic, pasture aeration offers the potential for added soil water penetration and reduced nutrient runoff by creating soil perforations ranging length from 5 to 15 cm using metal spikes that penetrate the soil to 15 cm depth. Also, the addition of gypsum can further reduce P runoff. We evaluate different pasture management scenarios that included gypsum application, spreading poultry litter, pasture aeration, or combinations thereof, to assess relative profitability, greenhouse gas (GHG) emission and nutrient runoff effects. Specifically, default values for nutrient runoff along with an evaluation framework as provided in decision support software, as attached, assist with the selection of field activities to perform to either enhance profitability by way of forage yield improvement or to estimate the cost of mitigating nutrient runoff or GHG emissions. Using Excel®’s VBA programming we develop a decision aid that collects relevant user-specific farm parameters and literature-based default values on nutrient runoff changes with the implementation of various practices to allow the user to conduct sensitivity analyses. A basic consequential life cycle assessment offers insight on expected greenhouse gas (GHG) mitigation potential by applying published GHG emission estimates associated with fuel and fertilizer use changes that were not calibrated in the field. A survey of producers that employed pasture aeration over a two year time period of free access to equipment was also conducted to at least capture some producer feedback. Results indicate that pasture aeration using rented equipment requires relatively little yield improvement (< 5%) to offer greater profit while reducing runoff. Given that pasture aeration is a time-intensive production practice, survey results are mixed in terms of producer willingness to adopt the practice. The tool lends itself to estimating operation-specific subsidies needed to encourage pasture aeration with the intent to reduce nutrient runoff, enhance forage yield, and thereby the feasibility of poultry litter application.