| Previous results showed that chemical treatments on raw rice straw could improve the decomposing efficiency of rice straw by microorganism. Chemical treatments could efficiently decrease the amount of waxiness, the cellulose, semi-cellulose and silicon dioxide of raw rice straw, while water-soluble compounds of the treated rice straw was increased and therefore the treated straw could be easily attacked by soil microorganisms. Pot experiments were carried out to study the effect of application of the chemically treated rice straw with inorganic fertilizer (urea) on soil microbial biomass nitrogen (MEN), microbial biomass carbon (MBC), and mineral nitrogen and crop growth in this paper. The results obtained were as follows:1. Pot experiments with winter wheat showed that both soil MEN and MBC were increased at the seedling stage of winter wheat. Soil MEN reached highest value at the booting stage of winter wheat, then decreased until the harvest period of winter wheat. The application of the treated rice straw with urea could increase soil MEN, MBC and mineral N by 180%, by 45% and by 66%, respectively during the whole growth stage of wheat, compared with control (CK), thus increasing the N uptake and dry weight of wheat by 56.3% and 124.3% respectively. Application of raw rice straw had not so remarkable effects on the supply of soil available N and N uptake by winter wheat as that of treated rice straw. Application of treated rice straw with urea significantly increased the grain yields of winter wheat and the N in wheat grains compared with the application of the raw rice straw with urea and application of urea only. Highest use efficiency of chemical N fertilizer was found in the application of treated straw with inorganic fertilizer among all treatments.2. Pot experiments with spinach showed that the application of rice straw increased the content of MBC and MBN in both Bungor Sandy clay loam soil and yellow-brown earth. The amount of MBC and MBN in the treatment of TS+N was higher than any other treatment on average during whole spinach growth. The changes of the MBC and MBN in Bungor Sandy clay loam soil were similar to those in the yellow-brown earth, i.e. theamount of MBC and MEN was increased greatly at the beginning of the experiment, and thereafter decreased in the fluctuant shape.3. Pot experiment with spinach also showed that in six treatments only FN and rice straw combined with inorganic fertilizer increased soil mineral nitrogen (NH4+-N and NO3--N) in both soils. And in these two treatments the changes of ammonium in Bungor Sandy clay loam soil was similar to that in yellow-brown earth, i.e. the content of NH4+-N in both soils increased rapidly at the beginning of experiment, and thereafter decreased gradually. In three nitrogen fertilizer treatments the NH4+-N content reached highest in 7 days, while in other three treatments without nitrogen fertilizer application the NH4+-N content reached highest after 2 days. The content of NH4+-N in the treatment of rice straw with inorganic fertilizer was lower at the beginning of spinach growth than that in the treatment of FN, which inferred that there could exist a competition between spinach and soil microorganism in N uptake.The content of NO3--N in yellow-brown earth gradually increased on the commence of the experiment and reached the highest value in 30 days, then declined, while the content of NO3--N in Bungor Sandy clay loam soil rapidly reached the highest in 7 days after treatment and thereafter decreased gradually. It was well known that high content of NO3--N enhanced the risk of its leaching in Bungor Sandy clay loam soil. Therefore it was practical and efficient to reduce fertilizer amount or change the fertilization in Bungor Sandy clay loam soil so as to prevent it from losing NO3--N at the beginning of fertilization. In our experiments we also found that application of FN increased soil mineral N rapidly while combined application of rice straw with inorganic fertilizer released soil mineral N slowly. Thus the soil appli...
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