Environmental optimization of systems of swine production

A model was developed in order to optimize under different constraints the production systems in a farm associating crop and fattening pig productions. For each simulation the model calculated the feed formulas (growing and finishing), the management of manure and the crop rotation and fertilization that maximized the gross margin. The model was first used to compare 9 different strategies of manure management (slurry ; solid manure ; slurry + solid manure ; compost of slurry ; compost of solid manure ; biological denitrification treatment ; biological treatment with separation of the solid fraction ; compost of slurry + exportation ; compost of solid manure + exportation). Up to 50 pigs produced/ha/year, the highest gross margin was obtained with the slurry strategy. Between 60 and 80 pigs/ha, the mix strategy "slurry + solid manure" was the most interesting. Above 90 pigs/ha/year, the strategy with compost of slurry and slurry treatment offered the best results. In overall, the gross margin was lower for strategies based on solid manure than for strategies based on slurry, mainly because of the requirement for straw. The environmental assessment revealed higher nitrogen and phosphorous balance excess for strategies based on solid manure, and higher ammonia volatilization for strategies based on slurry. The model was also used to study additional constraints such as limiting the spreading of organic phosphorous.This study reveals a strong link between animal and crop production. It also appears that good gross margin and low environment impact can be obtained with high intensity of pig productions per ha, if the right manure management system is used. However systems with low intensity are more sustainable, the optimum being around 50-80 pigs produced/ha/year.