Management model for assessment of nitrogen flow from feed to pig manure after storage in Vietnam.

Nitrogen (N) losses from pig production and the recycling of N from manure to crops can harm the atmosphere, soil and ground water quality. This study intended to build a dynamic management model, adapted to the Vietnamese context, that links the N flow at all stages along the manure management chain from the N in the diets fed to grower-finisher pigs to the application of the manure in the field. The model assesses N contents and losses at each stage of manure management so that application of manure N can be adjusted to ensure optimal fertilizer value, while at the same time minimizing environmental damage. This model provides a tool for examining the N flow on pig farms, to adjust the N content of feeds, the pig population, and to minimize N discharge and emissions. The model is developed using Powersim software and data from feed-excretion, storage and composting experiments. For validation and performance of the model we used sub-datasets from feed-excretion experiments in Denmark and Vietnam that were not used to parameterize in the model. This article presents the development of the model and trial of the model through scenario analyses of pig production in livestock production zones. The objective is that policy makers, extension officers or agricultural advisors will use the model as a support management tool to formulate and adjust manure management practices. This includes assessment of the land carrying capacity in existing livestock production areas and of maximum acceptable manure loads in planned livestock production zones.