Economic and environmental evaluation of dairy manure utilization for year round crop production
Somda, Zana Constantin
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Dairy farms with limited amounts of land potentially develop an imbalance of manure nutrients. Reducing the impact of excess on-farm manure nutrients on water pollution necessitates a method for determining carrying capacity allocating the manure supply. An efficient approach to address this problem requires balancing manure nutrient and crop uptake and crop nutrient and animal use. A whole farm linear programming model was used to balance animal nutrient use, plant nutrient production in manure, animal nutrient production by crops and manure nutrient utilization by plants. The theoretical underpinning of this analysis is expected utility maximization. The producer maximizes expected utility by considering milk production, manure production, the ability of crops to take up manure nutrients and the supply of forage for cow rations. This model is utilized to determine economically optimal dairy herd intensities, and crop mix for unrestricted and restricted scenarios of nutrient losses. Representative farm operations were simulated for dairies with 600 available cropland acres and flexible cow numbers and for dairies with 500 cows and flexible cropland acres that utilized manure for year round crop production. The results showed that farms were substantially affected by the imposition of restrictions on N and P losses, although profitability decreases were smaller on the farm when restrictions were imposed on N alone than farms when restrictions were on P alone. When a fixed land base was net returns to land and management was reduced by 5.8% and 56.8% on the farms with N and P restrictions, respectively, compared with 6.7 and 9.7% when acre adjustments were allowed for a farm with 500 cows. The model developed provides farmers with a tool most profitably meet current and future surplus nutrient applications. Whether dairy farmers are able to make cropland adjustments under N and P loss may well determine future sustainability and survival of the farming operations. If additional acres are not available or feasible to acquire, herd reductions may be necessary to meet restrictions on N and P.