Effects Of Fertilization And Straw Returning On The Components And Enzyme Activity Of Soil Organic Carbon

The object of our study is winter wheat and summer maize rotation ecosystem in ShaanxiGanzhong irrigated area. According to laboratory measurements and cultivation experiments，we studied the effects of six different fertilization treatments on the components and enzymeactivity of soil organic carbon as well as the respiration intensity of soil. The six treatmentsare: free-nitrogen application （N0），conventional nitrogen application （FP），recommendednitrogen application （N330）， reduced nitrogen application （N165）， increased nitrogenapplication （N495） and recommended nitrogen application+straw mulching（N330+S）. Thestudy provided the theoretical basis for the enhancement of soil fertility and sustainableagriculture development. The main results and conclusions are as followings:（1）The total soil organic carbon decreased with the increasing soil depth under differentfertilization treatments. Within0-20cm soil layer， N330+S treatment had the highest totalsoil organic carbon （TOC） content，14.732g㎏^-1， which significantly increased12.44%than FP. The next one was N330treatment，14.39g㎏^-1， which significantly increased11.92%than N0. Therefore，the order was: N330+S>N330>N165>N0>FP>N495. Within20-40cm soil layer， there was no significant difference of soil total organic carbon amongdifferent treatments， the order is N330+S>N165>N330>N495>N0>FP.（2）The content of different components of soil organic carbon decreased with increasingsoil depth under different treatments. Within0-20cm， the contents of soil water solubleorganic carbon （WSOC） were different among different treatments， but the difference wasnot significant. But within20-40cm soil layer， the order wasN330+S>N330>N495>N165>FP>N0. The content of WSOC of N165treatment decreased by37%compared with that in0-20cm soil layer. The contents of soil microbial biomass carbonwithin0-20cm soil layer under different treatments showed the following order:N330+S>N330>N165>FP>N495>N0. But within20-40soil layer， compared with N0theother treatments reached the significant level. The contents of soil readily oxidizable organiccarbon （ROC） within0-20cm under different treatments presented the following order:N330+S>N330>N495>N165>FP>N0， but within20-40cm soil layer the order was:N330>N165>N330+S>N495>FP>N0. Generally speaking， N330treatment was beneficial to the accumulation of the components of soil organic carbon， and the effect will be bettercoupled with straw mulching.（3） Fertilization and straw mulching enhanced the activities of soil invertase， urease，phosphatase at different levels within0-20cm and20-40cm soil layers. Within0-20cm soillayer， soil invertase activity of N330+S and FP， N165treatments had significantdifference， and the order was: N330+S>N330>N165>N495>FP>N0. Within20-40cm soillayer， the activity of soil invertase decreased with soil depth increased under the sametreatment. Soil invertase activity of N330+S and N495had significant difference，so did theN330and N0treatments. We can see the order was: N330+S>N330>N495>FP>N165>N0.Within0-20cm soil layer， the activity of soil urease between N0and FP treatments wassignificantly different， while the difference between N165and N330+S was also significant，and the order was N330+S>N330>FP>N495>N165>N0. Within20-40cm soil layer， FP andN0soil urease activity had significant difference，so did N165and N330+S. The activity of soil invertasedecreased with soil depth increased under the same treatment， and the order wasN330+S>FP>N495>N330>N165>N0. Nitrogen and phosphate fertilizer can dramaticallyimprove the activity of urease and phosphatase respectively. Within0-20cm soil layer， soilacidic phosphatase activity was different under different treatments， but the difference wasnot significant. Since we kept applying phosphate fertilizer at a constant level，100kg P2O5hm-per treatment， during five years experiment， and the degree of soil acidic phosphataseactivity can represent the supplu condition of soil rapidly-available phosphorus. Thus， soilacidic phosphatase activity remained almost stable within0-20cm and20-40cm soil layers，and the activity of soil phosphatase decreased with the soil depth increased.（4）Respiration intensity was different within0-20cm and20-40cm soil layer underdifferent treatments. Within0-20cm soil layer， soil respiration intensity constantly increasedduring the first three days of cultivation， and slightly decreased after the third day. Overallresults showed that comparing with N0treatment soil respiration intensity of the others hadsignificant differences. Soil respiration of N330+S treatment was relatively better than theothers. Within20-40cm soil layer， soil respiration intensity was different under differenttreatments， but the difference was not significant. Overally speaking， compared with N0treatment， soil respiration intensity of the others remarkably increased， and this was relatedto the content of soil organic carbon and microbial biomass carbon in soil. Soil respirationintensity decreased with the increasing cultivation time under different treatments. Soilrespiration intensity of N330+S treatment increased during the first two days of cultivation， but decreased from the third day. Moreover， compared with the other treatments， soilrespiration intensity of N330+S treatment was obviously higher.