Wednesday, 25 January 2017
Earthquake Recovery - calculating loss in production
Once the initial priorities of family home, access, fences and water has been addressed the impacts of slips on your farm business can be assessed and quantified.
First you will need to assess overall loss in production resulting from the slips, which are made up of two parts, face and tailings.
Face: Soil removed leaving a shallow soil or subsoil with low moisture holding capacity, little organic matter and very low nitrogen levels. Face slips are very slow to re-vegetate. The face generally only makes up 30% of the visual slip damage.
Tailings: The soil that was lost from the slip. Tailings are a tumbled mixture of the soil, rubble and buried vegetation. Tailing debris re-vegetates within 6-12 months due to existing plant material and from dormant seed already in the upper soil layer.
In some instances subsequent regrowth on these tailings is higher than the equivalent non-eroded slopes. It is appropriate to only consider the face as lost production.
Calculating immediate loss in dry matter
Estimate the percentage area of the slip face and the steepness involved (slips often occur on >28° slopes).
Generally this land has 60% of the productive capacity of flat/rolling country. Both pasture quality and utilisation is lower in steeper slopes.
Estimated loss in consumed dry matter as a result of varying slip damage on a Central North Island farm of average topography (27% flat/rolling, 48% hill and 27% steep hill).
|Topography||% of area affected|
|% of hill with slip face||0||2||3||5||8|
|% of slip on steep hills||3||9||15||25||42|
|Loss in annual consumed dry matter (%)||1||3||4||7||12|
Moderate slip damage often only produces the same loss in dry matter as a poor “growth” year.