Nutrient budgeting
Nutrient budgets offer insight into the balance between crop inputs and outputs. In short, they compare nutrients applied to the soil to nutrients taken up by crops. A nutrient budget takes into account all the nutrient inputs on a farm and all those removed from the land. The most obvious source of nutrients in this situation is fertilizer, but this is only part of the picture. Other inputs come with rainfall, in supplements brought on to the farm and in effluent – either farm or dairy factory – spread on the land. In addition, nutrients can be moved around the  farm – from an area used for growing silage to the area used to feed it out, from paddock to raceway, and within paddocks in dung and urine patches. Nutrients are removed from the farm in stock sold on, products (meat, milk, wool), crops sold or fed out off farm, and through processes such as nitrate leaching, volatilization and phosphate run-off etc. Importance. An accurate nutrient budget is an important tool to provide an early indication of potential problems arising from (i) a nutrient surplus (inputs>outputs), leading to an accumulation of nutrients and increased risk of loss or  (ii) a deficit (outputs>inputs), depleting nutrient reserves and increasing the risk of deficiencies and reduced crop yields. They also provide regulatory authorities with a readily-determined, comparative indicator of environmental impact. Overall, nutrient budgets help ensure that farming practices are conducted in an efficient, economic, and environmentally sustainable manner. Assumptions. A nutrient budget isn't as exact as a financial statement. An assortment of variables affects each tract of land. For example, some areas may have had too much manure applied over time or it may have been unevenly distributed, and previous flooding could affect results. Limits and  assumptions should be incorporated when compiling a budget including the average nutrient removal coefficient values if they are not specific to a certain field.