THE MICROBIOLOGICAL CHARACTERISTICS OF RED SOILS (I) THE MICROBIOLOGICAL ANALYSIS OF THE HILLY RED SOILS DERIVED FROM QUATERNARY RED CLAY OF CHHSIEN, WESTERN CHEKIANG

Red soils derived from quaternary red clay occur on the hilly land of Chuhsien, western Chekiang. The soils have been cultivated for a long time, and their fertility was definitely improved as the cultivation went on. Four samples of these soils of different fertility, varying in accordance with their history of cultivation, were used in this study, and the microbial population, rate of nitrification and cellulose decomposition, and the respiratory capacity of these soils were analysed 4 times annually. The results were summarized as following: 1. The abundance of soil microorganisms increased with the improvement of soil fertility. Among the microbial population, bacteria is the most abundant organism in all soils. The number of bacteria is relatively higher in more fertile soil, while the relative number of fungi is decreased as the cultivation went on. The abundance of aerobic cellulose decomposing organisms, the nitrifying bacteria and aerobic nitrogen fixing bacteria are also positively correlated with soil fertility. 2. The respiratory capacity, measured with Warburg apparatus, also increased with the improvement of soil fertility. 3. The rate of nitrification is very different in the tested soil samples. To those having higher fertility, 90% of the added ammonium was oxidized into nitrate within 1 week, and the process of nitrification was completed in 3 weeks. But a delayed nitrify- ing process was happened in virgin soil, only 20% of the ammonium was transformed into nitrate after 5 weeks. 4. The cellulose decomposing capacity of these soils, as measured by embedding cloth method, also showed good correlation to soil fertility. In the most fertile soil about 45-67% of the dry weight of the embedded cloth were lost within 1 month. But in the case of virgin soil, only 1.44-8.50% were lost. Using the soil particle inoculation method, it showed that the presence of cellulose decomposing microorganisms in most fertile soil was as high as 100% (mostly bacteria), while in virgin soil, there were only 8.75-62.50% (mostly fungi). 5. The isolation of Azolobacter chroococcum and Beijerinck sp. by plaque method, soil particle method and enrichment method was achieved only from the fertile cultivated soils. However, Clostridium pasteurianum was found in all soil samples. Survival of the inoculated Azot. chroococcum in different samples varied with the soil fertility. They sustained longer in cultivated fertile soils. These findings showed clearly that the fertility of red soils is characterized by some of the microbiological properties.