Nutrient budgets are comparisons of nutrients applied to the soil to those 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. [1]
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. [2]
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. [3]
Nutrient budgeting has expanded beyond traditional agriculture into Precision Turfgrass Management (PTM). Unlike uniform agricultural fields, urban landscapes and golf courses exhibit high spatial variability in soil composition. High-tech integration using GNSS and soil sensors allows for the creation of site-specific management units. By utilizing Variable-Rate Application (VRA), managers can balance the nutrient budget by applying precise amounts of fertilizer only where uptake potential is highest. This minimizes the surplus side of the budget, reducing nutrient leaching into urban watersheds. [5]
Within the framework of urban metabolism, the concept of Lawn Metabolism is used to quantify the total energy and material throughput of turfgrass systems. Lawns are characterized as high-turnover ecosystems where the balance between photosynthesis and respiration is managed through technical interventions.
Advancements in sensor technology, such as infrared gas analyzers (IRGA) and soil respiration probes, allow for the real-time monitoring of a lawn's metabolic state. These data points are used in precision management to adjust irrigation and fertilization "just-in-time," effectively treating the lawn as a self-regulating biological circuit. This metabolic modeling helps identify the point of diminishing returns where additional inputs (fertilizer or water) no longer result in increased biomass or carbon sequestration, but instead exit the system as waste. [6]