秸秆还田对长期连作棉田土壤有机氮组分的影响

Effects of Cotton Straw Incorporation on Organic Nitrogen Fractions in Long-term Continuous Cropping Cotton Field

探讨长期秸秆还田下连作棉田土壤有机氮组分的变化特征,对深入认识连作棉田土壤肥力演变及合理施肥均具有重要的理论价值。依据新疆绿洲棉花长期连作定位试验,设置秸秆还田条件下棉花连作5、10、15和20年(分别标记为5、10、15和20 a)及无秸秆还田处理下连作5、10、20年(分别标记为CK5、CK10和CK20)共计7个处理,采用Bremner酸水解蒸馏法对有机氮组分进行分级。结果表明:无秸秆还田处理下,随着连作年限的增加,土壤全氮明显增加,除氨基糖态氮逐渐下降,其他有机氮组分逐渐上升,但差异不显著(P>0.05)。与无秸秆还田处理相比,秸秆还田可以显著提高耕层土壤全氮和有机氮各组分含量,连作5、10和20年的土壤全氮分别比CK5、CK10和CK20增加了27.12%、29.56%、36.56%,差异显著(P<0.05);氨基酸态氮增加了44.93%、80.00%、61.11%,氨态氮增加了26.92%、34.48%和35.48%,氨基糖态氮增加了11.11%、62.50%、100%,未知态氮增加了11.56%、6.38%、24.59%,非酸解性氮增加了34.81%、13.16%、24.60%,连作20年均达显著水平(P<0.05),且随着连作年限的增加,各组分氮含量逐渐增加。同时,秸秆还田增加了氨基酸态氮和氨基糖态氮占全氮的比例,降低了酸解未知态氮比例,且随着连作年限的增加,氨基酸态氮比例上升,非酸解性氮比例下降。有机氮各形态在耕层土壤中的分布趋势为:非酸解性氮(173.32 mg·kg^(-1))>酸解未知氮(149.00 mg·kg^(-1))>氨基酸态氮(123.17mg·kg^(-1))>酸解氨态氮(100.42 mg·kg^(-1))>氨基糖态氮(30.42 mg·kg^(-1))。综上,秸秆还田能够提高长期连作棉田耕层土壤全氮和有机氮各组分含量,增强了土壤的供氮能力,提高土壤肥力水平。同时,秸秆还田增加了不易分解的酸解未知氮和非酸解性氮,维持了土壤氮库的稳定性。

Discussing the changing features of soil organic nitrogen components in long-term continuous cropping cotton field under the straw returning,it is of great theoretical value to deeply understand the evolution of soil fertility and rational fertilization in continuous cropping cotton fields.According to the long-term continuous cropping location test of cotton in Xinjiang Oasis,the research set up cotton continuous cropping under the condition of straw returning for 5,10,15 and 20 years(marked as 5 a,10 a,15 and 20 a respectively)and continuous cropping with no straw returning for 5,10 and 20 years(marked as CK5,CK10 and CK20),a total of seven treatment.And the organic nitrogen components were classified by Bremner acid hydrolysis distillation.The results showed that total nitrogen in soil significantly increased with the increase of continuous cropping years,and the other organic nitrogen components increased gradually except for ammonia sugar nitrogen under the treatments without straw returning to the field,but the difference was not significant(P>0.05).Compared with no-straw returning treatment,straw returning could significantly increased the content of total N and organic N fractions of plough layer soil.The total nitrogen in soil increased by 27.12%,29.56%and 36.56%respectively over CK5,CK10 and CK20 after 5,10,and 20 years of continuous cropping,and the difference was significant(P<0.05).Amino acid nitrogen increased by 44.93%,80.00%and 61.11%,ammonia nitrogen increased by 26.92%,34.48%and 35.48%,amino sugar nitrogen increased by 11.11%,62.50%and 100%;unknown nitrogen increased by 11.56%,6.38%and 24.59%,un-hydrolysable nitrogen increased by 34.81%,13.16%and 24.60%,continuous cropping for 20 years reached a significant level(P<0.05).And with the increase of continuous cropping years,the content of each nitrogen components gradually increased.At the same time,straw returning treatments increased the percentage of amino acid N and amino sugar N,while the percentage of unknown non-acid hydrolysis N decreased.And with the continuous cropping years,the percentage of amino acid N increased but non-acid hydrolysable N percentage decreased.Meanwhile the distribution trend of organic N fractions in cultivated soil followed the order of non-acid hydrolysis nitrogen(173.32 mg·kg^-1),hydrolysable unidentified N(149.00 mg·kg^-1),amino acid N(123.17 mg·kg^-1),acid ammonia N(100.42 mg·kg^-1)and amino sugar N(30.42 mg·kg^-1).In conclusion,straw returning can improve the content of total N and organic N fractions in long-term continuous cropping cotton field,enhance the soil N supply and increase soil fertility.In the meantime,the straw returning also increases the non-decomposable acid hydrolysis unknown N and non-acid hydrolysis N,so as to maintain the stability of the soil nitrogen reservoir.