Soil Characteristics Determine the Effect of Compost or Sterile Compost on Wheat ( Triticum aestivum L.) Development

Composted organic wastes are applied to crops as organic fertilizer and to improve chemical and physical soil characteristics, but the importance of microorganisms applied with the compost is still debated. In this study, composted cow manure was sterilized or left unsterilized and applied to two contrasting unsterilized soils, i.e., a soil identified by its high organic matter content (30.8 g C kg−1) considered the OM-rich soil and one by its low organic matter content (1.8 g C kg−1) considered the OM-poor soil. Both soils were subsequently cultivated with wheat (Triticum aestivum L.) in the greenhouse for 134 days. Application of the cow manure compost to the OM-poor soil increased plant height 1.1 and weight 2.4-times, although the application of sterile compost increased plant height 1.4 and weight 3.4 times at harvest. Application of compost or sterile compost to the OM-rich soil reduced wheat plant weight 1.3-times, but seed weight decreased 1.7 in the compost amended and 1.4-times in the sterile compost amended soil. These results suggest that microorganisms in soil and in the compost compete for nutrients with the plant. As such, application of compost as organic fertilizer to a crop cultivated in an organic matter rich soil might require the additional application of inorganic plant nutrients to compensate for possible nutrient immobilization by soil and compost microorganisms, and the amount supplied will depend on compost and soil characteristics.