Effects Of Rapeseed Cake On Biological Activities And Transformations Of Nitrogen And Phosphorus In Soil

In agriculture production,chemical fertilizers are playing more and more important role and the amount used is also increasing continually.The excessive use of chemical fertilizer causes several soil and environmental problems such as imbalance of soil nutrients,environmental pollution,soil acidification,depletion of trace element availabilities,decrease in activities of soil enzyme,and changes of microbial community and structure in soil and so on.The organic-fertilizer could improve physical and chemical properties of soil;provide nutrients for crops and energy for microorganisms,resulting in increasing soil nutrient bioavailabilities and the abilities of soil nutrient supply.The seed cake is the residue left after extraction of oil crops,the common we see is the soybean, rapeseed,sesame,cottonseed,peanuts,camellia seed,tung seed,and so on.Among them,the rapeseed cake is applied much more in South China.The experiment showed that employment of rapeseed cake in flue-cured tobacco production could improve the soil structure of tobacco filed, promote microbial activities,enhance the biological validity of soil nutrients and more importantly improve the appearance quality of tobacco leaf,increase the fragrance and improve the flavor evidently.We studied the effects of rapeseed cake on soil microbes,soil enzyme activities and soil available nutrients of the quaternary period yellow earth and purplish soil by indoor cultivation experiment,the purpose is to explore the mechanism of improvement of soil fertility and flue-cured tobacco quality with rapeseed cake.The experimental results are as follows:Following application of rapeseed cakes into soils,the numbers of bacteria,actinomycetes and fungus were significantly increased.The largest numbers were observed in the prophase and then reduced gradually.They reached the maximum at variable time according to microbial species in different soils.The largest numbers of both bacteria and fungi were similar in the two soils but actinomycetes were much more in purplish soil than those in yellow earth.After repeatable addition of rapeseed cake into soils three times,six strains of bacteria(2 strains of bacteria in yellow earth and 4 in purplish soil) and five strains of fungi(3 strain of Apodachlya in yellow earth and 2 in purplish soil) were isolated and identified.The protease activities in the soil with rapeseed cake added into are higher remarkably than the control.They were also higher in purplish than yellow earth and changed with the incubation time. The activities of protease reached highest at 5 days in yellow earth and 10 days in purplish soil, respectively,and then decreased as the time prolonged.The urase activities were increased remarkably at 10 days and reached highest at different time in the two kinds of soils and then decreased as the time prolonged.The urase activities in the purplish soil increased faster than yellow earth,but the maximum value in yellow earth is higher than purplish soil.The invertase activities of soils is remarkably reduced along with the mixed of rapeseed cake.The minimum value of invertase activity in two kinds of soil is similar.The catalase activities in two kinds of soil are similar,about 5 days reached highest,and then maintained at a steady state continuously.The contents of organic matter in the soil with rapeseed cake added into reached maximum value in 5～10 days,it in purplish soil was appreciably higher than yellow earth,and then decreased along with the time lengthened.The contents of total N of soil increased remarkably in 5days,it in purplish soil was appreciably higher than yellow earth,afterwards maintained at a steady state.The contents of available N of soil increased remarkably in 5days,it in purplish soil was higher than yellow earth.Then in yellow earth it maintained steady and increased in 30～40days;and in purplish soil it was increased continuously.The contents of available P of soil increased remarkably in 5days, it in purplish soil was higher than yellow earth.Then in yellow earth it maintained steady and increased in 30～40days;and in purplish soil it maintained steady in 5-20days and then increased remarkably.The contents of available K of soil increased remarkably and reached highest at 5days, the maximum values of two kinds of soil are similar,afterwards maintained at a steady state.There are different correlations in different soils among soil microbes,soil enzyme activities and soil available nutrients.In yellow earth,there were significant positive correlation between bacteria amount and contents of organic matter,significant negative correlation between bacteria amount and contents of available K,significant negative correlation between actinomycetes amount and contents of available N,significant positive correlation between fungi amount and urase activity; while in purplish soil,bacteria amount had significant positive correlation with invertase activity, highly significant positive correlation with contents of organic matter,highly significant negative correlation with contents of available N,and significant negative correlation with contents of available K.