Composting and Tillage Effects on pH and Cation Exchange Capacity.

Cultivation of arid soils in southeast Idaho have reduced soil organic matter (SOM) levels which may have negatively  impacted soil chemical properties such as increased pH and decreased cation exchange capacity.  Alternative management practices like reduced tillage and compost application may positively influence soil pH and CEC. The objective of this study was to determine if compost and reduced tillage increases SOM and decreases pH.  The crop rotations consisted of four year wheat, wheat, alfalfa, and potatoes rotation and a two year wheat and potato rotation.   Treatment rotations were conventional tillage, composted with tillage, minimum tillage (tillage only before and after potatoes), and a control (two year rotation with intensive cultivation).  Compost source was steer feedlot manure (11.2 g kg^-1 N and 7.0 g kg ^-1 P) and was fall applied at the rate of 11.2 Mg ha^-1.  Research plots were located on a Blackfoot silt loam and a Pocatello variant silt loam near Rexburg, Idaho.  Soil pH for the 2 year rotation did not change from spring 2007 to fall 2009 (pH = 7.2).  The four year rotations (conventional tillage, composted, and minimum tillage treatments) showed a pH decrease of 0.2 to 0.3 over three years (2007-2009). The pH results suggest a decrease of pH may be the result of a longer rotation, 2 years of alfalfa, or a combination of rotation length and alfalfa.  Comparison of CEC among treatments for 2007 and 2009 showed no difference (CEC ranged between 17.6 – 20.0 cmol_c kg^-1).  The CEC results coincide with soil organic matter (SOM) results which have shown no increase from 2007 – 2009 among treatments.  The reason for no change in SOM and CEC  may be due to cooler temperatures which may have reduced mineralization rates of compost and surface residue (reduce tillage).  The study may need more time before changes in SOM will occur which may influence CEC and pH.