Soil Conditioning Index

The Soil Conditioning Index (SCI) has been used for a primary performance measure by four watershed councils in northeast Iowa.  The SCI was chosen as a performance measure because of its focus on soil organic matter.  Farmers in these watershed understand the importance of maintaining and building soil organic matter in order to maintain productivity.

The SCI is a product of the RUSLE2 soil loss computer model, predicting the effect of cropping systems and tillage practices on Organic Matter (OM) reported on a scale from -1 to +1. The three main components are organic matter returned or removed from the soil, the effect of tillage and field operations on OM decomposition, and effect of predicted soil erosion associated with soil conservation and other field management. Major contributing practices to increase index scores include: Forage or small grains in rotation, contouring, reduced tillage and especially no-till planting, and fall cover crop planting following corn silage or soybean harvest.  A negative SCI value predicts declining OM, while a positive value predicts increasing OM. The Natural Resource Conservation Service required a SCI value of 0 or above to be eligible for the original Conservation Security Program.

Variations of the following “per-farm” SOIL CONDITIONING INDEX incentives have been used in four watersheds.

  • $200 first year payment per 0.1 SCI above 0 for whole farm weighted average of all fields.
  • $100 per 0.1 SCI for annual data and SCI review after the first year.
  • $200 paid for each 0.1 improvement in the annual SCI.

To determine the the SCI on each farm, a technician works with the farmer to document management practices.  This information is combined with soil and landscape characteristics within the RUSLE2 soil loss calculator.  A weighted average SCI is then calculated for each farm.  Field and farm results are provided to cooperating farmers.  The farmers also receive a listing of all the fields in the watershed – listed by highest Phosphorus Index to lowest Phosphorus Index.  The SCI values are highlighted in a separate column in the report.  To review a real-world example, the 2009 Coldwater-Palmer watershed summary can be found here and includes watershed average values for six years.

Rye Cover Crop

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