Effects Of Different Straw Returning Methods On Soil Organic Carbon Sequestration And Crop Production

With the development of modern intensive agriculture and the extensive use of chemical fertilizers,the soil fertility,especially the organic matter content in farmlands of China showed an obvious downward trend of decrease,which seriously affected the quality of agricultural products and production efficiency.It was truely importment to increase investment of organic matter,thus promoting the research and exploration of scientific use of straw and other agricultural wastes fertility.On the other hand,the industrial structure of agriculture in China was during the adjustment period when crop straw and animal manure processing problems remained to be resolved.In this paper,we aimed to the way of straw returning in order to improve soil fertility and crop yield and at the same time promote soil organic carbon fixation,and provide reference to mitigate the greenhouse effect.To comprehensively evaluate straw utilization effects on soil organic carbon sequestration and crop growth in farmland,a field experiment was carried out in Jiangsu Academy of Agricultural Sciences Luhe test plots.Different straw utilization methods including spent pig litter compost(SP),straw and manure compost organic fertilizer(OF)and wheat straw biochar with fertilizer(BR)were compared.These three materials were applied according to the criterion of applying same amount of nitrogen,and no fertilization(CK)and single fertilizer((NH4)2SO4 + Ca(H2PO4)2 + KCl)(CF)were set as control.Rice-wheat rotation ecosystem was used.Soil samples were collected two months and one year after fertilization at August 16,2015 and June 16,2016 at 0-5 cm,5-10 cm and 10-20 cm soil depth.At the same time crop growth and yields were recorded.The soil organic carbon(SOC)content and variation coefficient of soil organic carbon were affected by different straw returning methods.In top soil layer,SOC content in OF,SP,BR were 4.32%,18.27%,and 9.30%higher than that in CF,respectively,two months after straw returning.One year later,SOC content in OF,SP,BR were 18.82%,10.98%and 11.76%higher than that in CF,respectively.This suggests that a large number of foreign carbon inputs can improve soil total carbon and contributed to the improvement of soil fertility.Compared with the soil carbon content the two months after straw returning to soil,the soil carbon stratification was more obvious one year later.SOC distribut in among soil layers ranged in the order of 0-5cm>5-1 Ocm>10-20cm.Pure chemical fertilizer application sigificantly reduced soil C/N in one year.Compared with chemical fertilizer,OF and SP improved soil water-soluble and humin carbon contents in subsurface soil.The addition of organic manure increased PQ values,HA/FA ratio,E4/E6 values and ? log K.The correlation analysis showed significant or extremely significant positive correlations among humic material,humic acid,fulvic acid and total organic carbon.The correlation coefficients were between 0.714 and 0.834.The correlation between humin carbon and total organic carbon content was the best with a correlation coefficient at 0.834.Soil microbial community structure and function showed significantly differences under different straw-returning modes.The microbial carbon metabolism,microbial diversity index and carbohydrat,amino acid,polymers and amine utilization were significantly higher in OF treatment than in others.The influence of SP application on microorganisms was less significant than that of OF,BR,and CF.The influences of BR and CF on soil microbial indexes were similar in topsoil(0-5cm).The different straw returning modes could significantly affect soil microbial carbon metabolism in soil surface layer(0-5cm).The effects on subsurface layers(5-10 cm and 10-20 cm)were less obvious.Compared with CF and BR,OF and SP increase soil microbial diversity.These findings indicated that OF and BR application could effectively increase soil carbon metabolic diversity in short term.The CO2 flux of soil under different straw returning methods was influenced by the season and farmland management measures.Except that CO2 flux(averaged 1.44 n mol·m-2·S-1)was highest in OF during the first quarter of rice growing.CO2 flux was highest in CF in the first and second quarter of wheat and rice seasons which averaged 5.34nmol·m-2·s'1 and 1.33 nmol·m-2·s-1,respectively.Relationship between soil CO2 flux and soil temperature showed power function.The correlation coefficients of OF,SP and CF were 0.48,0.64 and 0.52 respectively.The soil temperature was affected by different ways of straw returning to field.During the three seasons of crop rotation,the soil temperature of CF,BR was lower than in OF and SP.In this paper,the yield of rice and wheat under BR was slightly higher than that of CF treatment,and the yields under rice in the two seasons were 9.69%and 5.74%higher than that under CF,respectively.The alkali hydrolyzable nitrogen in surface layers of BR and CF was significantly different(P<0.05)in two periods.Soil available phosphorus and available potassium were slowly released.In the topsoil and subsurface layer,the pH were 6.00,6.08 in BR,while pH were 5.74 and 5.94 in CF.There was no significant difference between OF and SP which were significantly lower than that of CF and BR.The effects of different straw returning methods on soil available nutrients were mainly in the topsoil.In the short term,OF and SP could reduce the soil bulk density.However soil available nutrients showed no significant difference among treatments.