The Studies Of Microbial Diversity Under Different Planting-patterns For Paddy Soils In Southern China

Microbial organisms play a key role in the agricultural ecosystems, involving in cycling of energy and nutrient, formation and decomposition of soil organic matter, maintenance of soil productivity, growth and disease protection of plants. A series of experiments on basis of three field trials were carried out employing tranditional soil microbial methods and molecular method (denaturing gradient gel electrophoresis, DGGE) to research the influence of three cropping-patterns in Southern China on soil nutrients, major microorganism number, soil enzyme activity, community structure of microbial. The main results were as follows:1. Contents of different soil nutrients were generally higher in the 0~15cm layer than in the 15~30cm layer for all the three cropping-patterns. The rice-vegetable cropping system was beneficial to increase the content of soil organic matter in 0~15cm depth.compared with that of egetable monoculture and fallow rotation cropping system, the difference was significant. The sequence of hydrolysable N content for the three cropping systems both in 0~15cm and 15~30cm were vegetable monoculture>rice-vegetable>fallow rotation cropping system. The contents of available P and exchageable K were vegetable monoculture>fallow rotation cropping system>rice-vegetable both in two layers. The contents of available P had no regulatiy. Meanwhile, the rice-vegetable system increased soil pH value, but monoculture of vegetables decreased it.2. The influence on the number of the soil microorganisms including bacteria, fungi and actinomyces was investigated. The number of bacteria and actinomyces could be ranked for the three cropping patterns as: 1) vegetable monoculture< fallow rotation cropping system < rice-vegetable, however, the number of fungi was in an opposite direction. 2) The number of soil microorganisms was higher in the 0~15cm than in the 15~30cm layer. 3) The number of of soil microorganisms did not varied obviously in different seasons for the three cropping patterns.3. The activities of some major soil enzymes including intervase, acid phosphatase, urease, polyphenoloidase and catalase were analysed. Results showed that the activities of different enzymes were higher in the 0~15cm than in the 15~30cm layer. The activities varied in the trends of vegetable monoculture