Effect of vermicompost and pelleted manure as amendments on chemical and biochemical properties of soil under greenhouse farming

Soil organic matter (SOM) plays an important role in conservation and restoration of soil fertility, as it is able to ameliorate physical, chemical and biochemical soil properties preventing erosion, increasing porosity, water-holding capacity and cation exchange capacity. Furthermore, SOM can stimulate microbial biomass and as consequence microbial activity and functionality in terms of soil respiration and enzymatic activities. Biogeochemical cycle of nutrients can also take advantages from the microbial activity enhancement with positive effects on N and P uptake and crop yields. The intensive farming systems favour the SOM decomposition and depletion due to the absence of rotations, the preference of milling to ploughing, the mineral fertilization, and the removal of crop residues.

The aim of this research was to assess the effect of vermicompost (VC) as organic soil conditioner compared to pelleted manure (PM) under greenhouse in a conventional farm. Two doses of VC and PM corresponding to 75 and 150 kg N ha^-1 year^-1 were applied to solarized soil. Solarization was carried out during the hottest summer period and applied to all plots to control weeds, nematodes and soil-borne pathogens. VC is the final product of a vermicomposting process involving synergistic action of earthworms and microbes in the bio-conversion of organic matter into humus-like substances. VC used in this research derived from solid digestate obtained in anaerobic digestion plant using, as carbon source, livestock sewage, olive mill wastewater and whey from dairy industry. Chemical and biochemical properties of soils sampled after 7 and 150 days from organic amendments were investigated to understand the correlation between the use of organic soil conditioners and organic C stock, nutrient availability, microbial biomass, enzymatic activity, and crop yields and quality.

In the first sampling PM increased significantly the soil electrical conductivity compared to VC amendments. In addition, PM, in particular the greater dose, enhanced better than VC soil respiration, microbial biomass and overall enzymatic activities because PM is richer in labile carbon source than VC. In contrast, VC was able to improve the activity of acid phosphatase and urease by increasing the applied dose thus making free phosphate and ammonium from organic matter.

This study is part of the project "Sustainable management of soil fertility in the Sele Plain to produce ready-to-eat food as cover crops through organic amendment deriving from local livestock sector" funded by PSR Campania 2014/2020.