Biochemical properties of two different textured soils (loam and clay) after the addition of two different composts during conversion to organic farming

Abstract

The conversion to organic farming of two soils, a loam (Xerofluvent) under irrigation and a clay (Chromic Haploxerept) under dryland management, was studied through analysis of their biochemical properties. Soil biological status was evaluated by measuring microbial biomass carbon and the ratio of enzymatic activity to microbial biomass. Results were compared to those after application of inorganic fertilizer. At the end of the study, in both soil types the organic treatments had increased the organic matter and nitrogen content compared with the inorganic treatment. Total organic carbon (TOC) values in the clay were higher than in the loam. This could be related to a lower mineralization rate of soil organic matter under dry land management and/or with a protection effect, by the clay on the organic fraction. However, absolute ratios of some enzymatic activities (dehydrogenase, protease and alkaline phosphatase) by microbial biomass carbon in the clay were lower than in the loam indicating a lower rate of enzyme production by microbial biomass in the clay. In the clay soil there was a great increase in TOC, total N, microbial biomass and enzymatic activity, in all treatments, in the last crop cycle. This was mainly related to a previous legume crop. Generally organic management improved biomass and enzymatic activity in both soils. In the future further studies are required to confirm the positive long-term effect of organic fertilization on biochemical properties which maintain or improve soil quality.