Effict Of Straw On Carbon,Nitrogen Transformation In Different Soybean-corn Cropping Soils

In this paper,the methods of combination of field experiment and indoor soil incubation (simulating straw returning all)were used to study the effect of straw on soil enzyme activity, DOM and carbon,nitrogen mineralization in rhizosphere zone and non-rhizosphere of soybean,corn and mixed cropping fields.Results of the study showed that:1.MBC,MBN,inorganic nitrogen and respiration quantity of planting soil presented different change trends in different ways by adding straw;with straw content and incubation time increasing, MBC of soybean field soil gradually reduced; with incubation time increasing, MBC of corn field soil gradually reduced, and there were no significant differences between corn field soil MBC and straw addition content, but significant differences between non-rhizosphere soil MBC and corn field soil. MBC rosed at the beginning then declined in mixture cropping soil,and with straw content increasing, MBC gradually increased; there were no significant differences with non-rhizosphere soil.MBN rosed at the beginning then declined in soybean field soil,and increased with straw content increasing, and reached a significant difference level among straw contents. After incubation,both MBN of corn field and mixed farming soil had no obvious changes, at the initial stage of incubation, there was no significant difference between MBN of corn field soil and straw content, and MBN of mixed farming soil gradually reduced with the straw content increasing;soil inorganic nitrogen content in soybean field and mixed farming had no significant differences with straw addition content, but had a significant difference with the root zone soil. Inorganic nitrogen content in soybean field soil gradually rose with the increase of incubation time, and that of mixed farming soil had an adverse trend instead, decreased slightly over time. Inorganic nitrogen content in corn field soil rose after incubation, and increased with straw addition content.There were significant differences between total soil respiration and straw addition content in three different planting soils,and total soil respiration all increased gradually with straw content increasing.Total soil respiration prented as:2times straw>1times straw>without straw.The respiration rate had the same change trends, and significantly different with the straw addition amount.2.Soil urease,invertase,polyphenol oxidase and catalase of different planting soil presented different change trends in different ways by adding straw,soil urease activity of three different planting made different changes after straw added.At the initial stage of incubation,urease activity of soybean field soil declined with straw content increasing；by contrast,urease activity of mixed farming soil increased with straw content increasing,but there was no significant difference between urease activity of corn field soil and straw content. With straw addition into three different planting soil,invertase activities increased with straw content increasing.During incubation,invertase activities of different planting soil declined and then increased again, but changed at different range. Soil polyphenol oxidase had different change trends with other enzymes.Polyphenol oxidase activity in soybean field and mixed farming soil both rose with straw content increasing.During incubation,polyphenol oxidase activity of soybean field soil first fall then increased quickly,and that of mixed farming soil increased gradually with incubation time.Polyphenol oxidase activity of corn field soil reduce with incubation time,and had no significant difference with straw addition content.There was no significant difference between catalase activity and straw addition content in the three different planting soils,but significantly different with that of non-rhizosphere soil.Catalase activities of soybean field and corn field soil gradually reduced with incubation time,but that of mixed farming soil increased gradually with incubation time;In addition, the total soil respiration of three different planting soils reached significant and very significant different levels with four enzyme activities,respectively.3.Reducing sugar,phenolic compounds and DOC of different planting soils by straw addtion presented different change trends.Reducing sugar content of soybean field and corn field soil increased with straw increasing, and that of soybean field and mixed farming soil first decreased then increaseed,but that of corn field soils firstly increased then reduced.Phenolic compounds content in three different planting soils decreased with incubation time,and all reducesed with straw content increasing.Phenolic compounds content in mixed farming soil were significantly higher than that of soybean field and corn field soil.DOC contents of three different planting soils were gradually fallen after incubation.DOC in soybean field and mixed farming soil increased with straw added. DOC contents in corn field and mixed cropping soils were significantly higher than that of soybean field soil.