Introduction
Nutrient budgets:
Crops and animals require nutrients in order to grow and reproduce. Manure and fertilizer are applied to cropland to supply nutrients to crops. Ideally, harvested crops feed animals that produce more manure, and so the cycle continues.
Although nutrients are transferred between crops and animals, a balance in the flows of nutrients between the crops and animals within a geographic region is not guaranteed. Fertilizer is usually purchased into a region to sustain crop production, while feed is imported to support animal production. Although imported fertilizer can be managed to closely match the nutrient needs of crops, imported feed nutrients are usually based on animal needs rather than crop nutrient needs. The result is that the amount and proportion of nutrients in manure may not match local crop needs.
An agricultural nutrient budget is a summary of the major nutrient inputs and outputs to cropland within a geographic region. The difference between the nutrient inputs and outputs is the nutrient balance. If the nutrient balance is positive, more nutrients are added in fertilizer and manure applications than are removed by crops. Likewise, if the nutrient balance is negative, more nutrients are removed by crops than are supplied by manure and fertilizer.
