| In order to probe into the effect of minimum tillage, no-tillage and Astragalus sinicus straw on biological character in soil and to provide scientific proof for reasonable culturing system to fertilize soil, studies on the effect of no tillage and minimum tillage on the biological activity in paddy soil covered with 33% rice-straw (about 2500 kg·hm-2)and the ways and quanity of incorporating Astragalus sinicus straw on microbial quantity, microbial activity and enzyme activity in soil during different tobacco growth period were conducted. The results showed that:1. It was different for the effect of culturing system on biological activity in soil.The soil biological quality can be improved by minimum tillage and no tillage. Minimum tillage and no tillage can do good to the growing crops and rice-straw-decomposing when a little rice-straw was returned to soil. During late-rice maximum tillering stage, the activities of cellulase in soil are no tillage>tillage >minimum tillage, the activities of catalase and xylase in soil are minimum tillage> no tillage>tillage, the activities of urease and protease in soil are tillage> minimum tillage> no tillage, nitrification activities in soil are no tillage>minimum tillage> tillage, and the microbial activities and ammonification activities in soil are minimum tillage> tillage>no tillage. During the late-rice-harvested stage, the activities of urease, catalase and xylase in soil are minimum tillage> no tillage> tillage, but the microbial activities, protease, cellulase, ammonification activities and nitrification activities in soil are tillage> minimum tillage> no tillage.2. It was different for the effect of returning ways of Astragalus sinicus straw, such as full-thickness tillage covered with 22500 kg·hm-2 A. sinicus straw on soil surface, full-thickness tillage with 22500 kg·hm-2 A sinicus straw deep in soil and full-thickness tillage without A. sinicus straw, on biological activity in soil. The full-thickness tillage with 22500 kg·hm-2 A. sinicus straw deep in soil was the optimal ways to improve soil quality. The quantity of aerobic bacteria decreased rapidly at the early tobacco'growth stage, and slowly increased at the middle tobacco growth stage and then slightly fluctuated. The quantity of aerobic bacteria in soil with 22500 kg·hm -2 A. sinicus straw deep in soil was more than that covered with 22500 kg-hm 2 A. sinicus straw on surface. The quantity of fungi decreased during the whole tobacco growth period. The quantity of fungi in soil covered with 22500 kg·hm-2 A. sinicus straw on surface could be inceased during early tobacco growth period. The quantity of fungi in soil with 22500 kg·hm-2 A sinicus straw deep in soil was affected a little. The quantity of actinomycetes decreased at the early tobacco growth stage, followed by a sharply increase at the middle tobacco stage, and finally gradually increased at the late tobacco stage. Thequantity of actinomycetes in soil covered with 22500 kg·hm-2 A. sinicus straw on surface was more than that with 22500 kg·hm-2 A. sinicus straw deep in soil, and more than that without A. sinicus straw. Microbial activity decreased at early tobacco stage, then continually increased at the later stages. Until the later tobacco stage, the microbial activity in soil covered with 22500 kg·hm-2 A. sinicus straw on surface was more than that with 22500 kg·hm-2 A. sinicus straw deep in soil, and more than that without A. sinicus straw. Cellulase activity increased before growth vigorous stage and decreased after that. Cellulase activity in soil with A. sinicus straw was more than that without A. sinicus straw. Urease activity dropped sharply, followed by slightly increase, then sharply increased at late tobacco growth stage. Urease activity was the highest in soil with 22500 kg·hm-2 A. sinicus straw deep. Protease and catalase activity were not serious during the whole growth period. They both slightly decreased at the early growth stage. They were the highest in soil with 22500 kg·hm-2 A. sinicus straw deep.3. It was obviously different for the effect of A. sinicus straw quantity, such as 0 kg·hm-2 (contrast),15000 kg·hm-2,22500 kg·hm-2,22500 kg·hm-2 (reducing N, P and K from A. sinicus) and 30000 kg·hm-2 A. sinicus, on microbes quantity,microbial activity and enzyme in tobacco soil. The optimal returning quantity of A. sinicus straw for tobacco growth was 22500 kg/hm2. Aerobic bacteria quantities increased rapidly in the early growth stage during tobacco growth, then increased slowly. During the early tobacco growth stage, the aerobic bacteria in soil with 22500 kg·hm-2 (reducing N, P and K from A. sinicus) A. sinicus were more than that in soil with 22500 kg·hm-2 A. sinicus.The quantities of actinomycetes decreased slowly in the early growth stage, and increased little in the medium-term stage and decreased later. The actinomycetes in soil with A. sinicus was more than that in the CK soil. The actinomycetes in soil with 22500 kg·hm-2 (reducing N, P and K from A. sinicus) A.sinicus were less than that in soil with 22500 kg·hm-2A. sinicus. Fungi quantity increased rapidly in the early and medium-term stages, decreased afterwards. Soil microbial activity decreased in the early stage, then was stable, finally gradually increased and reached the highest peak. Soli microbial activities increased with more A.sinicus straw to soil. Cellulase activity increased before blossom stage and decreased after that. Initially, urease activity started by a sharp decline, and then increased slightly, but sharply increased during the late stage. Cellulase activity in soil ith A. sinicus straw was higher than that in soil without A. sinicus straw. Urease activity increased with more A. sinicus straw to soil. Protease activity decreased in the early stage, and increased slightly later. Protease activity increased with more A. sinicus straw to soil. Alterations of catalase activity in soil were not serious in the whole tobacco growth stages.
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