水稻秸秆还田年限对稻麦轮作田土壤碳氮固存的影响

Effects of years of rice straw retention on soil carbon and nitrogen sequestration in rice-wheat system

为明确连续秸秆还田对农田土壤碳氮固存的影响,该文于扬州大学试验场展开研究。田间试验布置于2010年,设置秸秆不还田(NR),秸秆还田1a(SR1),秸秆还田2a(SR2),秸秆还田3a(SR3),秸秆还田4a(SR4),秸秆还田5a(SR5),秸秆还田6a(SR6),秸秆还田7a(SR7),秸秆还田8a(SR8)9个处理。于2018年小麦收获后取样,测定分析了土壤容重、有机碳和全氮含量,计算碳氮比、层化率、土壤有机碳和全氮储量(等质量法)。结果表明,随着秸秆还田年限的增加,各土层有机碳和全氮含量逐渐提高,但增幅逐渐减小。0～5 cm土层土壤碳氮比在短期内(≤3 a)随着秸秆还田年限增加而显著提高,但是对其他土层和年限的无显著影响。随着秸秆还田年限增加,表层0～5 cm与其他层次有机碳和碳氮比层化率先增长后下降,全氮层化率则先下降后上升。秸秆还田处理0～20 cm土壤有机碳和全氮储量分别较NR提高6.23%～27.85%和6.04%～25.66%,各土层碳氮储量均随着秸秆还田年限的增加而提高,但是当还田年限>6a其增幅明显降低。综上所述,秸秆还田具有良好的碳氮固存效应,但是当秸秆还田年限>6a,土壤碳氮固存量的增幅明显降低,可适当减少还田量。

Growing concerns about environmental conservation and sustainable intensification have raised interests in enhancing soil organic carbon and nitrogen pools.To estimate the effects of straw retention years on soil organic carbon and nitrogen pools,a field experiment initiated from 2010 with 9 straw retention year treatments(no straw retention,NR;1,2,3,4,5,6,7,8 straw retention years were SR1,SR2,SR3,SR4,SR5,SR6,SR7,SR8,respectively)was conducted in a rice-wheat double cropping system at Yangzhou University Experimental Station in Yangzhou on the Middle-Lower Yangtze Plain of China.After 9 years of experiment,soil bulk density,soil organic carbon(SOC)and total nitrogen(TN)were determined from 3 soil depths increments.Then the C:N ratio,the stratification ratio and the storage of SOC and TN(using the equivalent soil mass approach)were calculated.This study observed that with the increase of straw retention years,the soil bulk density at 0-20 cm depth decreased gradually.Compared with NR,the soil bulk density at 0-5,5-10 and 10-20 cm depths showed significant differences(P<0.05)from SR3,SR1 and SR1,respectively.The concentrations of SOC and TN increased gradually with the increase of straw retention years,but the increase amount decreased gradually.There was no significant difference of SOC and TN concentrations between SR6,SR7,and SR8 treatments.Compared to NR,the contents of SOC at 0-5,5-10 and 10-20 cm depths under straw retention treatments(SR1-SR8)were improved by 6.37%-30.99%,10.13%-32.04%and 4.15%-24.08%,respectively,while the TN contents were increased by 4.81%-22.00%,6.86%-29.38%,5.15%-22.48%,respectively.The soil C:N ratio at 0-5 cm depth increased significantly with the increase of straw retention years in short term(≤3a),however there were no significant difference between treatments at the other soil depths or years of straw retention.With the increase of straw retention years,the stratification ratio of SOC and C:N ratio in 0-5 cm to the other depth rose first and then fell,but that of TN decreased first and then rose.The stratification ratios of SOC,TN and C:N ratio for 0-5:5-10 cm were among 0.95-1.00,1.02-1.11,0.87-0.97,respectively,while for 0-5:10-20 cm it was among 1.02-1.11,1.16-1.21,and 0.85-0.95,respectively.The stocks of SOC at 0-5,0-10 and 0-20 cm depths under straw retention treatments were 6.37%-30.99%,8.27%-31.52%and 6.23%-27.85%higher than those of NR,respectively,those of TN stocks were 4.81%-22.00%,5.78%-25.14%and 6.04%-25.66%higher than those of NR,respectively.The SOC and TN stocks increased with the growth of straw retention years at each layer,along with the gradual decrease of increase amount,especially after the 6 years of straw retention.There was no significant difference of SOC and TN stocks between SR6,SR7,and SR8.Above all,straw retention was benefit to SOC and TN sequestration.However,after 6 years of straw retention,the growth rates of soil carbon and nitrogen stocks were significantly reduced,which could be considered to reduce the amount of straw retention.