| The rise of CO2concentration in atmosphere has some connection with the massconsumption of industrial fossil fuels as well as the agriculture production.In recent years, dueto the special climate condition and the unwise regulation of farmland, CO2emissions offarmland soil has been significantly increased followed by the decline of carbon reserves insoil year by year, while carbon reserves is one of the key factors determining farmlandproductivity, stable and high yield.Although China is a major consumer of fertilizer,theutilization efficiency is rather low,and the excessive use of fertilizer tends to rendering thepollution of underground water and the decrease of soil fertility. Modern agriculture arerequired to fulfill the conception of green, organic and low-carbon agriculture, which needs toseek for more scientific fertilizer method under the condition of less use of fertilizer.Therefore,in our study we discussed the effect of the reduction of chemical fertilizer, theincrease of organic fertilizer and straw on soil carbon characteristics, above and undergroundbiomass on the basis of long term location test,offering scientific evidence for rationalfertilizer, increase of organic carbon in farmland and strengthening of crop carbon fixationcapacity. Our results are as follows:1. The effect of organic fertility betterment with the reduction of chemical fertilizer onthe content of carbon among different organ in summer-sown maizeThe content of carbon among different organ in summer-sown maize presents thefollowing pattern: grain>stamen>stem>leaf>bract>thrum>root. Root, stem, leaf and stamenall share a similar trend of first rise and then down at tasseling, anthesis and elongation stage.At tasseling stage, compared with fertilizer only, fertilizer reduction with the adding oforganic fertilizer(method Ⅰ) and fertilizer reduction with the adding of straw(method Ⅱ) canboth boost the content of carbon in maize root by23.04%and22.36%,respectively; Thecarbon content in stem treated by method Ⅰ is increased by0.26%than treated by method Ⅱ;the carbon content in stamen treated by70%reduction of fertilizer while increasing strawpresents significant distinction with those treated by fertilizer only (P<0.05). At anthesisstage,the carbon content in root treated by method Ⅱ is decreased compared with thosetreated by fertilizer only while increasing the amount of organic fertilizer will increase the carbon content in root among different treatments; The carbon content in stem treated bymethod Ⅰ and method Ⅱ is increased by36.63%and38.28%compared with those treatedwith fertilizer only. At maturing stage, all treatments can strikingly increase the carboncontent in grain, and the carbon content in above section (stem, leaf) is increased significantlythan underground section (root).2. The effect of organic fertility betterment with the reduction of chemical fertilizer oncarbon reserves of whole plantUnder the treatment of organic fertilizer reduction,the carbon content of above groundorgan (leaf, stem and grain) is significantly higher than underground organ (root),50%reduction of fertilizer with the increase of straw and50%reduction with the increase oforganic fertilizer significantly reduce and enhance the carbon content in undergroundsection,respectively. Compared with fertilizer alone,30%reduction of fertilizer with theadding of straw could elevate the carbon content in whole plant; fertilizer reduction with theadding of organic fertilizer of different treatments can all boost the carbon content in wholeplant,and the degree of increase is especially striking on the above ground part.3. The effect of organic fertility betterment with the reduction of chemical fertilizer onthe amount of fixed carbon in summer-sown maizeThe amount of carbon fixation of different organs in maize shows the followingtrend:grain>stem>bract>leaf>root>stamen>thrum.The regional carbon fixation of the twomethod(Ⅰ and Ⅱ) is elevated by10.87%and11.62%compared with fertilizer alone. Ofthem,the regional carbon fixation reaches its maximum by the combination of chemicalfertilizer and low amount of organic fertilizer, and the average regional carbon fixation ofdifferent treatments by the application of chemical fertilizer in concert with organic fertilizeris higher than treatment of the same amount reduction of chemical fertilizer with straw.4. The effect of organic fertility betterment with the reduction of chemical fertilizer onthe overall organic carbon content in soilDuring summer-sown maize growth season,the overall organic carbon in soil isdecreased from seedling to elongation, and increased gradually from elongation to mature.From elongation to tasseling,to flowering and mature stage, the overall organic carbon contentin soil is increased by7.35%,2.30%and5.16%, respectively. The overall organic carboncontent in soil treated by method Ⅰ and Ⅱ is1.95%higher and8.11%lower than thosetreated by chemical fertilizer alone. In comparison with the use of chemical fertilizer alone,the average of overall organic carbon content ranging from0-60cm soil treated by method Ⅰis elevated1.95%. With the increase of soil depth,the mass fration of the overall organiccarbon in soil is decreased gradually and reaches statistically extremely significant difference. In comparison with the use of chemical fertilizer alone, the overall organic carbon in soilranging between0-20cm treated by method Ⅰ and Ⅱ is increased by11.21%and0.13%, theoverall organic carbon in soil ranging between20-40cm as well as40-60cm treated bymethod Ⅰ is decreased by8.70%and6.22%, while the decreasing extents are17.16%and11.59%for method Ⅱ.5. The effect of organic fertility betterment with the reduction of chemical fertilizer onactivated organic carbon in soilActivated organic carbon in soil ranging between0-60cm demonstrates the followingtendency at varied developmental stages:elongation<seedling<tasseling<flowering<mature,from elongation to tasseling,to flowering,to mature, the activated organic carbon in soil isincreased by9.56%,3.32%,8.17%, outnumbering the increased extent of overall organiccarbon in soil. Compared with chemical fertilizer alone, the mass fraction of the overallorganic carbon in soil ranging between0-60cm among different treatments of method Ⅰ allreaches significant difference, the detailed results are as follows:70%reduction of chemicalfertilizer by adding organic fertilizer(3.7763g/kg)>50%reduction of chemical fertilizer byadding organic fertilize(r3.6887g/kg)>30%reduction of chemical fertilizer by adding organicfertilizer(3.3540g/kg)>30%reduction of chemical fertilizer by adding straw(3.3020g/kg)>chemical fertilizer alone(3.2927g/kg)>50%reduction of chemical fertilizer by adding straw(3.2113g/kg)>70%reduction of chemical fertilizer by adding straw(3.0923g/kg).The overall activated organic carbon in soil is decreased with the deepening of soil, theactivated organic carbon in soil attains signnificant difference among0-20,20-40and40-60cm soil. Among different layers of soil treated by method Ⅱ(0-20,20-40,40-60cm), theactivated organic carbon in soil is3.65%,3.23%,15.79%higher than control, while theincreasing ratios are9.11%,8.25%,19.35%by method Ⅰ.6. The effect of organic fertility betterment with the reduction of chemical fertilizer onregulatory index of soil carbon poolAmong different treatments of0-60cm soil, the average of soil carbon pool activityillustrates the following pattern:chemical fertilizer alone(0.465)<30%reduction of chemicalfertilizer by adding organic fertilizer(0.485)<70%reduction of chemical fertilizer by addingstraw(0.495)<50%reduction of chemical fertilizer by adding straw(0.519)<30%reductionof chemical fertilizer by adding straw(0.539)<50%reduction of chemical fertilizer by addingorganic fertilizer(0.557)<70%reduction of chemical fertilizer by adding organic fertilizer(0.567); The soil activity index treated by method Ⅰ shares the same trends with theactivity of soil carbon pool as is detailed in the following:0-20cm<chemical fertilzieralone,20-40,40-60cm>chemical fertilzier alone; The soil carbon pool index of all other treatments is decreased except for treatment of70%reduction of chemical fertilizer by addingorganic fertilizer. The regulatory indexes of soil carbon pool of different treatments of methodⅡ and Ⅰ are105.596and118.547,and they have5.09%and15.65%increase compared withthe use of fertilizer alone.Our results indicate that method Ⅱ and Ⅰ both can strengthen the capacity of carbonfixation in crop and increase carbon reserves in farmland.Thus our study reveals that methodⅠ can not only reduce fertilizer pollution, but it also can fully utilize straw and organicfertilizer, thereby paving the way for low carbon agriculture as well as agriculture sustainabledevelopment. |
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