High densities of Collembola and mites in organic fields with undersown catch crops

The abundance and species composition of soil living mites and Collembola were investigated in autumn and winter in field plots with five different types of catch crops and a control plot that was kept free of vegetation. The catch crops, chicory, white clover, garden lupine, and perennial ryegrass were undersown in barley while fodder radish was sown after harvest .The investigation was carried out at a site on sandy loam and a site on coarse sand. At the sandy site densities up to about 250.000 and 100.000 m-2 of mites and Collembola, respectively, were found. At the sandy loam site densities were up to 120.000 mites m-2 and 150.000 Collembola m-2. The densities of both microarthropods were extremely high with up to 120,000 Collembola m-2 and 90,000 mites m-2. At the sandy site the Collembola were significantly more abundant in plots with catch crops than in the control plots during the winter. At the sandy site the prostigmatic mites showed significantly higher abundance in plots with catch crops, while the Collembola density was not significantly affected. The most abundant Collembola were Mesaphorura sp., Lepidocyrthus cyaneus, Isotomurus palustris and Sminthuridae sp. at the sandy loam, and Isotoma tigrina at the coarse sand. At both sites the mite fauna consisted mainly of Prostigmatic mites. The input of organic matter from the catch crop root exudes, the lack of tillage after harvest and the continuos plant cover are supposed to improve the conditions for the microarthropods in the catch crop plots.