Effects Of Different Organic Materials On Soil Organic Carbon Fractions And Aggregates Of Lou Soil

Shaanxi Guanzhong Plain is one of the main grain producing areas in China,the problem of soil quality degradation widely exists because of the highly intensive planting method of winter-wheat and summer-corn rotation.The returning of organic materials can improve soil structure,regulate soil nutrient balance,and increase soil organic carbon.However,the influence mechanism of different organic materials on the stability of soil aggregates is different.Thus an incubated study was conducted to explore the effect of different organic materials application dosages?0%,1%,2%and 4%?on the dynamic changes of organic carbon fractions and aggregate stability under different incubation time?60th,120th,180th,240th,300th and 360th days?.Soil organic carbon?SOC?and its fractions such as light fraction organic carbon?LFOC?,polysaccharides,water soluble substance?WSS?,fulvic acid carbon?FAC?,humic acid carbon?HAC?contents and aggregate stability were measured to study the stability mechanism of soil aggregates under the four organic materials amendment,path analysis was adopted in order to provide theoretical support for the soil structure and quality improvement of farmland.A three-year field experiment was carried out in order to explore the effect of different fertilizers on the aggregate size and the distribution of aggregate carbon,seven treatments were?1?control?no fertilization?,?2?chemical fertilizer?NPK?,?3?chemical fertilizer?10?straw?SNPK?,?4?chemical fertilizer+manure?M₁NPK?,?5?chemical fertilizer+high level of manure?M₂NPK?,?6?chemical fertilizer+manure+microbial agent?M₁NPKM'?and?7?chemical fertilizer+high levels of manure+microbial agent?M₂NPKM'?,respectively.The main results were as follows:?1?The SOC,soil light fraction ratio and WSS of 1%-4%application rates under corn straw and wheat straw increased by l22.8%-86.7%and 27.5%-92.0%,78.0%-479.4%and113.0%-505.4%,81.2%-247.8%and 53.3%-189.6%respectively,The LFOC increased by230.3%-331.4%under biochar treatment,HAC and FAC increased by 42.48%-88.26%and3.30%-46.85%under organic fertilizer treatment,and increased with increasing the organic material application rates,but the soil polysaccharide did not change significantly under the biochar treatment,while the HAC/FAC ratio only increased significantly under the biochar treatment at the end of incubation compared with the control.The application of corn and wheat straw decreased the organic carbon content of>2 mm aggregate in soil,while increased the organic carbon content of micro-aggregate?<0.25 mm?,and promoted distribution of soil organic carbon to macro-aggregates?>0.25 mm?.Organic fertilizer application could increase organic carbon content in all soil aggregates,but not effectively increased the carbon sequestration capacity of soil macro-aggregates.Biochar application mainly increased the organic carbon content of>2 and<0.25 mm aggregates,and the organic carbon proportion in the macro-aggregates increased before 300th days.The application of four organic materials had a most significant effect on the polysaccharide content of 2-1 mm and<0.25 mm aggregates.The proportion of organic carbon and polysaccharide in soil macro-aggregates did not change significantly in the organic fertilizer treatment,while there was a decreasing trend at 180th,240th and 360th days,respectively under wheat straw,biochar and corn straw treatment.?2?With the increase of the organic materials application rates,the content of>2 mm mechanical stability aggregate and<0.25 mm water stability aggregate decreased,while the other aggregates increased.As compared to the control,the aggregate mean weight diameter?WMWD?of water stability increased by 1.8-4.1 times,9.4%-60.1%,1.4%-36.0%and 2.1-3.0 times,the percentage of aggregate destruction?PAD?decreased by 37.8%-86.0%,2.5%-14.7%,10.0%-40.5%and 42.2%-79.5%under the 1%-4%application rates of corn straw,organic fertilizer,biochar and wheat straw treatments,respectively.The content of>0.25 mm water stability aggregate(WR_0.25)increased by 1.3².4 times,14.7%⁸8.6%and 1.2².2 under the 1%-4%application rates of corn straw,biochar and wheat straw treatments,respectively,and increased by 49.21%under the 4%application rates of organic fertilizer.and the WR_0.25.25 decreased at 360th,180th,240th and 180th days under corn straw,organic fertilizer,biochar and wheat straw treatments,respectively.Correlation analysis showed that the effect of WSS on the stability of soil structure was similar to that of SOC under the organic fertilizer treatment,and the effect of soil LFOC,WSS and HAC on the stability of soil aggregates was almost equivalent to the SOC,but less than that of organic carbon under biochar treatment.The effects of soil polysaccharide and WSS on soil aggregate stability were greater than SOC under straw treatment.The results of path analysis showed that the direct factors of soil aggregates stability were>2 mm and<0.25 mm aggregates under the conditions of applying four organic materials,while the indirect factors were different.For example,the application of corn straw decreased the<0.25 mm aggregate content by increasing the content of soil polysaccharide,HAC,WSS and>2 mm water stable aggregates,resulting in an increase in WMWD.Organic fertilizer application increased the SOC,causing<0.25 mm aggregate to form>2 mm large aggregate,thereby as a result of the increase in WMWD.?3?Under the field conditions,in the 0-10 cm soil layer,SNPK treatment increased the>5 mm mechanical stability aggregate content,and decreased the 1-0.5 mm aggregate mechanical stability content of soil,and NPK treatment increased<0.25 mm aggregate content.In terms of water stability of soil aggregates,the content of<0.25 mm aggregate decreased under NPK treatment,the content of 0.5-0.25 mm aggregate increased under SNPK,M₁NPKM'and M₂NPKM'treatments.Compared with CK,SOC increased under straw and manure treatments.The organic carbon content in 0.5-0.25 mm aggregate increased under NPK and SNPK,while the organic fertilizer application could increase organic carbon in all aggregates sizes.The above results indicated that the application of corn straw,organic fertilizer,biochar and wheat straw could increase soil organic carbon and its fractions,and biochar application mainly increased soil LFOC,Straw application mainly increased soil polysaccharide,light fraction ratio and WSS,organic fertilizer application mainly increased soil HAC and FAC,which affected the stability of soil aggregates by affecting these different fractions.Four organic materials could improve the stability of soil structure under this conditions,the higher the dosage,the more significant the effect.In terms of improving the stability of soil structure,corn straw>wheat straw>biochar>organic fertilizer,but in the maintenance of water aggregate stability,corn straw>biochar>organic fertilizer and wheat straw,carbon and polysaccharide sequestration capacity of macro-aggregate:straw>organic fertilizer and biochar.