Composting Effects on Soil Fertility and Physical Properties of Low Organic Matter Soils in Southeast Idaho.

Reduced crop yields and potato tuber quality are suggested to be related to intensive cultivation in a potato/grain rotation system in southeast Idaho which results in low soil organic matter and subsequently decreases soil health.  Application of soil amendments (e.g., compost and manure) can improve yield potential, increase soil fertility and organic matter content.  A continued study has proposed that the effects of soil amendments benefit the levels organic matter (OM), nitrogen (N), phosphorus (P), yield, and tuber quality.  A four year rotation (winter wheat, winter wheat, alfalfa, and potatoes) with compost added before planting was compared to the same rotation without a soil amendment.  The compost was steer feedlot manure (11.2 g kg^-1 N and 7.0 g kg ^-1 P) and was applied before planting at the rate of 6.7 Mg ha^-1 for wheat and alfalfa and at 11.2 Mg ha^-1 for potatoes.  Research plots were located on a Blackfoot silt loam and a Pocatello variant silt loam near Rexburg, Idaho.  Bulk density and soil fertility samples were taken in the spring and after harvest and compared to native soils from the original year which included undisturbed soils from the same soil type as the research plots.  Native soils had a bulk density of 1.14 g/cm³ which was lower than the plot bulk density of 1.51 g/cm³.   For the research plot soils, CEC ranged from 12 to 15 cmol_c kg^-1 and yields for 2007 were 4.36 Mg ha^-1 for wheat, 6.71 Mg ha^-1 and 22.6 Mg ha^-1 for potatoes.  No statistical differences were observed between crop yield and quality for the compost and the control treatments.  Soil tests showed that SOM in the research plots 19.3g kg^-1 and 43.3g kg^-1 for the native soils. The plots had lower fertility levels (e.g., total N and nitrate) than the native soils with the exception of phosphorus levels which were 73 kg ha^-1 for native soils and 88 kg ha^-1 for plot soils. The study is currently in second year of 12 years, and it is expected that composting will increasing soil carbon levels and provide nutrients to the plant which will reduce the amount of fertilizers need to obtain optimal crop yields and quality.