On organic farms, where external inputs are restricted, soil fertility needs to be maintained by balancing nutrient removal in produce with inputs from acceptable sources. Nutrient budgets at farm/field level are a useful tool for evaluating sustainable nutrient management and the environmental risks of different farming systems. Nutrient budgets can be applied to both major and micronutrients. The calculation can reveal unexpected sources, losses and imbalances of nutrients. Understanding how efficiently nutrients are used can help decision making in relation to rotation design, manure management and choice of inputs.