Discussion on Unexpected Outcomes from Overseer Output Based on GSL Modeled Farm Production Data.
- Soil Type is significant in quantifying total leaching of farm and precise identification of effluent and cropping areas may significantly affect real average losses N losses for total farm. (see table 1.0)
- Ensuring all Soil Types are specifically identified for a particular farm may be critical in lowering Overseer’s reported N leach total for farm. (see table 2.0)
- N leaching for crop production particularly when grazed where grown appears to inversely reduce the cropping areas N leach when yield of crop is increased over low yielding crop. This can be very significant in quantifying the farms total average N leach per Ha. (see table 3.0)
- Relationship between the applied N on a reducing scale being replaced by natural N on an increasing scale but averaged annually may give an incorrect total N leach assessment relative to the real usage/benefit of the actual time of applied N use. (see table 4.0)
- Analysis identifies an apparent discrepancy between N applied and N “used” when pasture DM yield. Pasture yield response to applied N does not appear to be accounted for in Overseers output.
- Inability to identify and quantify N leach and surface water run off and drainage losses when grazing crops under wet winter conditions.
- Rainfall effect which increases fracleach but does this increase diminish GHG total?
- Cultivation effect for cropping may be a variant that can reduce leaching of N through the Overseer model.
- Total Milk production is the primary connection in Overseer to N leach outcomes. Is sufficient account taken of the effect per cow production will have on the N leach outcome?
- Overseer appears to reduce the volume of N as a less productive system introduces more applied N to the system.
1.0 Overseer N Leach Variance for Soil Type and Rainfall
Rotrua Farms – Base Scenario
2.0 Overseer N Leach Variance for Soil Type Rainfall & Crop
Rotorua Farms – Base Scenario
Rotorua Farms – Base No N Scenario
3.0 Fodder Crop Yield Influence on N Leach Result
4.0 Test for N Leached with Variable Clover Content of Pasture