Effects Of Straw Returning And Nitrogen Amounts On Soil Carbon Pool And Radiation Use Of Double Cropping Maize

The unreasonable used of nitrogen increased the environmental load and seriously affected the soil quality.Straw returning is an measure to effectively improve the soil quality.The field experiment was conducted from March 2018to December 2019,at the experimental station?22°50?N,108°17?E?of Agricultural College of Guangxi University.The maize?Zea mays L.,var.Zhengda 619?was hand-planted at 55556 plant/ha,with 0.6 m row spacing and0.3 m plant spacing.with three replicates.The experiment adopted a two-factor split-plot design,and the main plot were traditional planting?TP?and full straw return?SR?;the subplots were five nitrogen levels:100 kg/ha?N100?,150 kg/ha?N150?,200 kg/ha?N200?,250 kg/ha?N250?,300 kg/ha?N300?.We discussed the straw return and nitrogen application on photosynthetic physiology,soil nutrients,soil organic carbon components and yield of maize,in order to provide theoretical basis for continuous straw return to reduce nitrogen application,the result as follows:1.In spring and autumn maize growing season,compared with the traditional planting straw,the return could improve the leaf area index?LAI?,chlorophyll content index?CCI?,dry matter weight?DM?,net photosynthetic rate?Pn?,canopy photosynthetic active radiation capture ratio?CR?and penetration ratio?PR?,reduced the reflection ratio?RR?.The canopy photosynthetic active radiation RR of straw return was significantly reduced by23.42%?spring maize?and 31.62%?autumn maize?than that of traditional planting,respectively?P<0.05?.Tr was significantly positively correlated with LAI,CCI,DM,Pn and CR?P<0.01?,and increased with the increase of the nitrogen amounts,and the increase range decreased gradually.2.Straw is rich N,P and K,which play an important role in soil nutrient.In the growing season of spring maize,the straw return decreased the content of TN and NH4⁺-H,and increased the content of NO₃^--N,available P and available K compared with the traditional planting.In the growing season of autumn maize,the straw return significantly increased the content of TN,NH4⁺-H,available K and available P,and significantly decreased NO₃^--N compared with the traditional planting?P<0.05?.There was a positive correlation between nitrogen amounts and soil nutrient,and nitrogen amounts was significantly positively correlated with NO₃^--N and available P?P<0.01?.Increasing nitrogen amounts is beneficial to improve the soil nutrients,the content of TN,available K and available P in soil could be increased by strew return continuously.3.In spring maize growing season,the soil organic carbon?SOC?,labile organic carbon?LOC?,microbial biomass carbon?MBC?of soil were 9.34 g/kg,2.60 mg/kg,137.13 mg/kg respectively?straw return?and 9.25 g/kg,2.44 mg/kg,84.30 mg/kg respectively?traditional planting?.In autumn maize growing season,the SOC,LOC,MBC of soil were 9.91 g/kg,2.47 mg/kg,111.89 mg/kg respectively?straw return?and 9.23 g/kg,2.11 mg/kg,92.05 mg/kg respectively?traditional planting?,and the straw return was significantly higher than those of traditional planting?except the LOC of autumn maize??P<0.05?.Nitrogen amounts was significantly positively correlated with SOC,LOC and MBC,straw treatments,nitrogen amounts,and their interaction significantly affected the MBC at R6,strew return continuously was very beneficial to improve soil SOC.4.In spring maize growing season,straw treatments,nitrogen amounts,and their interaction significantly affected the thousand grain weight?P<0.05?,the grain number/row,thousand grain weight,radiation use efficiency and yield of straw return were 2.10%,5.63%,10.43%and 10.59%higher than those of the traditional planting,respectively.In autumn maize growing season,straw treatments,nitrogen amounts,and their interaction significantly affected the grain number/row,thousand grain weight and yield?P<0.05?,the grain number/row,thousand grain weight and yield of straw return were 4.39%,5.69%and 14.37%significantly higher than those of the traditional planting,respectively?P<0.05?.The straw return could improve plant height,ear height,stem diameter,ear diameter,ear length,row number,and grain number/row,shorten ear tip.The yield increased with increasing nitrogen level,and there was no significant difference between 200-300 kg/ha of nitrogen amount,the yield of250 kg/ha was the highest,and the yield of 200 kg/ha was higher than those of traditional planting under different nitrogen application level.In this experiment,the yield of straw returning combined with 250 kg/ha nitrogen application was the highest,in order to ensure the yield of maize,the nitrogen amounts not less than 200 kg/ha,and the yield will decrease when the nitrogen amounts is more than 250 kg/ha.