Soil quality, microbial functions and tomato yield under cover crop mulching in the Mediterranean environment

• Tomato yield and soil responses to cover crop mulching were assessed.
• Two fields experiment (years 2012 and 2013) were carried out in a Mediterranean area.
• Cover crop mulches were: hairy vetch HV, lacy phacelia LP, and white mustard WM.
• LP mulch showed higher decomposition rate and lower tomato yield under arid conditions.
• The effects of mulches on soil quality and tomato yield depend on summer weather.

An experiment concerning the biological and chemical responses of soil to cover crop mulching was carried out in two adjacent experimental fields (2012 and 2013) under different climatic conditions in the Mediterranean environment (Central Italy). The Monthly Aridity Index was calculated in order to verify the relationship between soil properties and climatic factors under three different cover crop mulches: Vicia villosa Roth (HV), Phacelia tanacetifolia Benth. (LP), and Sinapis alba L. (WM). A conventional management was also included in the experimental fields as control (C). Soil samples were collected at 0–20 cm depth after the transplanting and the harvesting of tomato (May and August, respectively), in order to assess the initial and residual effects of mulching on soil quality. In the two experimental years, the amount of precipitation from May to August was 110 mm in 2012 and 172 mm in 2013. The average values of AI were 18 and 49 in 2012 and 2013, respectively. LP mulching was sensitive to low precipitation levels in terms of aboveground decomposition rate (the variation of dry matter from May to August 2012 was −53% in LP, 64% in HV and 69% in WM) and a lower tomato yield compared to the control in 2012 (4.2 kg m−2 in LP and 5.2 kg m−2 in C). WM mulching was sensitive to low precipitation in terms of soil nutrient storage (from May to August 2012 the variation of soil C was 19% in WM., 6% in C, −5 % in LP and 10% in HV; the variation of soil N was 44% in WM, 2% in C, −2% in LP and 13% in HV). Soil microbial activity and functional diversity were strongly affected by the climatic conditions in all mulching treatments. In particular, precipitation influenced soil C availability, which enhanced microbial functional diversity. In short, the effects of lacy phacelia, white mustard and hairy vetch mulching on soil quality, microbial functions and tomato yield were influenced by summer precipitation and temperature in the Mediterranean environment.