Effects of solarisation combined with compost on soil pathogens and the microbial community in a spinach cropping system

Abstract

This study compares the effects of solarization combined with compost (72% vineyard prunings and 28% leek residues) (CAS) versus solarization (NAS) in soils used for intensive spinach cultivation in the Mediterranean area. The objective was to study the beneficial effects of the compost on the soil microbial community, soil fertility and soil functionality related to C and N cycling during solarization, during the spinach crop growth period and after harvesting. CAS did increase soil fertility and microbial activity, in addition, CAS increased the microbial alpha diversity in the soil to a greater extent than NAS, and the Principal Coordinate Analysis (PCoA) of the beta diversity in the soil revealed changes in the bacterial and fungal community at the different sampling times, except after the plastic was lifted. During solarization and after harvesting, different beneficial bacteria and fungi related to C and N cycling were more abundant in CAS than in NAS, in the same way as the genera involved in plant defense and plant growth (Pseudomonas, Sphingomonas, Bacillus, Thermomyces, Streptomyces, NMD1 or Nitrospira). CAS also had a notable effect on the abundance of predictive genes involved in the C and N cycles. The functional genes showed their lowest activity level a week after covering the soil with plastic, but they increased after lifting the plastic and after harvesting. Compared to NAS, CAS also showed higher N2-fixation and greater conversion of N2O to N2. Moreover, the abundance of several predictive genes involved in hemicellulose, lignin and cellulose degradation suggested that CAS produced an increase in nutritional availability. From this study, it can be concluded that the combination of solarization and compost increased soil fertility, microbial activity, microbial diversity and functionality. Compost could provide added value by stimulating the microbiological community in the soil until harvest.