Changes in soil organic matter and biomass of soil microorganisms in alternative farming system

The object of this work was to find out the effect of ploughing-down all crop by-products (plant residues) to the content of soil organic matter and carbon biomass of soil microorganisms. A stationary experiment was conducted on Orthic Luvisol in warm and medium dry climatic region with the mean temperature of 9.7 degree C and the mean precipitation of 561 mm in year (south-western region of the Slovak Republic). In 1994-1997 the following crop were cultivated on experimental plots within the four-course system: - maize (cv. Dea), - spring barley (cv. Jubilant), - pea (Pisum sativum, cv. Olivin), - winter wheat (Triticum aestivum L., cv. Vlada). Two variants of farming system (fertilization) were applied in the experiment: rat. - rational fertilizing with mineral fertilizers, which rates were calculated at average yield level; p.zv. - decreasing organic matter was supplemented by ploughing-down of all crop by-products (plant residues) into the soil along with an addition of nitrogen to support the mineralization of wheat and barley straw plus mineral fertilizer supplementation for balancing. Soil was cultivated conventionally on all experimental plots with ploughing up to the depth of 0.3 m in maize and up to 0.2 m in other crops. During of the vegetation period (from March to September), five or six soil sampling were performed out from 0.02 to 0.2 m layer of the soil. Carbon biomass of soil micro-organisms (C mic) was determined in fresh soil samples. Content of oxidizable organic carbon was determined in air-dried samples according to Tjurin. Soil organic matter balance was calculated using the model of Jurcova et Bielek [ref. 7]. The results were estimated statistically by programme Statgraphics. The results show that addition of organic matter in form of all crop by-products (plant residues), improve of balance soil organic carbon on active to medium passive, in comparison with fertilization without application. These facts did not confirm in measured content of oxidizable organic carbon (C ox). The quantity of soil microbial biomass values (C mic) as a variable part of organic matter, were significantly influenced (alpha = 0.05) by ploughing-in of crop by-products. Soil parameters (C ox, C mic) were significantly affected by climatic conditions during experimental years. Cultivated crops did not influence on these parameters