The interdependent effects of solar disinfestation and compost maturity level on soil microbial activity

The combined effects of soil solarization and application of compost of various maturity levels upon soil microbial activity were studied under field conditions during 2010–2012. Eight treatments were divided into solarized and non-solarized treatments, and each was either non-amended or annually amended with compost at 6 kg (DW) m^-2. The composts were mature, partially mature, or immature. In all three tested parameters of microbial activity (respiration rate, heat output, and dehydrogenase activity) the immature compost showed higher activity than the other compost types. Soil samples were collected weekly in order to assess microbial activity, which was evaluated from measurements of soil respiration rate, heat output, and dehydrogenase activity. Significant and year-to-year reproducible differences in all three parameters were observed between soils amended with the three compost types. Some residual (carry-over) effects of previous-year treatments were obtained. Microbial activity decreased in both solarized and non-solarized treatments during the experimental period, probably because of increasing summer temperatures, but the decline was sharper in the solarized treatments probably due to oxygen deficiency under the tarp. Significantly higher activity was found in the treatments amended with the immature compost, both in the solarized and non-solarized treatments. This could be a result of the high level of dissolved organic matter in the immature compost, which enhanced microbial activity.