Microbial and physico-chemical responses of the soil to intensive onion and pepper cropping

Vegetable cropping systems are high-input and generally require large quantities of fertilization, protection, frequent irrigation, and repeated tillage operations. Consequently, an increase in vegetable production may have serious impact on soil health and functions. The aim of the study was to assess microbiological, chemical and physical indicators of soil fatigue in two of the most intensive vegetable crops in Poland: onions and peppers, to identify which cultivation practices are most responsible for the adverse changes. The results have shown, that the most reliable indices in cultivation of these vegetables occurred dehydrogenase activity, organic matter content and soil physical properties. The other studied parameters such as pH, nutrients availability and microbial abundance seem to be less sensitive factors. In all soils, where the onion and pepper were produced, the dehydrogenase activity was significantly lower as compared to non-cultivated soil. It corresponded with reduced content of organic matter. In onion production numerous runs by agricultural machinery during field operations lead to soil compaction, breakdown of its structure and organic matter reduction. Moreover, poor crop rotation and low surface coverage with vegetation accelerate these effects and deteriorate the biological functioning of the soil. In turn, in pepper cultivation, monoculture with high mineral fertilization, cause soil acidification and adverse effect on microorganisms, decreasing their activity, but increasing the proportion of fungi in microbial community. Intense mineral input, resulting in high concentration of nutrients in soil, may be a reason of reduced organic carbon content, despite application of organic manures.