A farm is a living system, comprised of soil, plants and water, and often with animals. Many of these things contain nutrients and nutrients sustain all living organisms. A living system is a hugely complex thing to understand and a farm adds to that individual practices and preferences that impact on the nutrient cycling processes.

OVERSEER is a mathematical model that captures the complexity of nutrient cycling in a farm system to help farmers and growers understand the way nutrients flow through their farm.

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OVERSEER does this by modelling how nutrients coming into the farm (such as fertiliser and feed) are naturally processed by organisms (such as cows, sheep and plants) and/or transformed by physical processes (nutrient cycles) and how nutrients move within the farm. 

Water coming into the farm (rain and irrigation) and plants that absorb nitrogen from the atmosphere (such as clover) also play an important role in the transfer of nutrients, and these are captured in OVERSEER.

Nutrients end up in plants (like pasture or maize) or as products leaving the farm gate (meat, milk, crops, wool and wine). For farms that produce animal products, when the pasture (or feed that is bought in to the farm) is eaten by farm animals, the nutrients they absorb are used to create product or excreted as dung and urine. The excreta is deposited on the soil or farm structures and can end up in an effluent system to be re-deposited elsewhere on the farm. OVERSEER uses information about how a farm is run to predict nutrient movement within the farm.

Depending on the local climate, management practices, how absorbent the soil is or how much water is draining through the soil; OVERSEER predicts what nutrients will be lost from the farm or be held in the soil to be re-used by plants. These losses include emissions into the air, losses through the soil (leaching) and losses across the land surface (run-off). 

The vulnerability of nutrients to these losses depends on the nutrient (N, P, K, S, Ca, Mg, Na), where on the farm they are deposited and in what form (urine, dung, effluent, fertiliser). OVERSEER uses mathematical calculations to capture these complexities to produce the nutrient budget.