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How pasture inputs impact the model

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Summary

Different types of fertiliser can be added to blocks by month. Overseer defines a set of products and their nutrients for the major NZ fertiliser companies. If there is not an appropriate product to select from, custom fertiliser and hence nutrient compositions can be created.

How pasture impacts the model

The following diagram depicts what parts of the model the pasture information entered in OverseerFM impacts. For a full interactive view of the scientific model in its entirety please click here

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Summary

Each pasture block has a pasture type and whether it is grazed (pastoral) or harvested (cut and carry). If the block is grazed runoff characteristics are also required.

Impact

Pasture type impacts metabolic energy and nutrient content of pasture and hence uptake of animals. Run off characteristics effect the surface runoff and hence drainage.

Details

The pasture type provides the model with the ME content and nutrient concentrations of animal feed. This drives the nutrient uptake of the animals and hence nitrogen levels in excreta.

As described, ME from pasture production is driven by the animal numbers and existing supplementary feed. Therefore, if animal numbers and supplementary feed remains the same but pasture type changes, the ME requirements are unchanged, but DM and nutrient intake may change.

Runoff characteristics

The runoff characteristics affect the nutrient runoff from the block.

  • Naturally high water table: Is used in riparian/wetland model, does not affect hydrology and hence losses from block.

  • Compacted: Soil water contents in top layer is reduced if soil is compacted.

  • Hydrophobicity: Describes the susceptibility of water to infiltrate or runoff at the soil surface. Is used in hydrology model to define runoff. Default is based on region and rainfall.

  • Susceptibility to pugging: This is not a measure of whether pugging has occurred, or the degree of pugging that occurs after a single grazing event but rather the propensity of pugging. This is used to estimate the profile drainage status, and in the estimation of denitrification.

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