秸秆还田对苏打盐碱稻区土壤团聚体分布及有机碳含量的影响

Effects of Straw Returning on Distribution of Soil Aggregates and Content of Organic Carbon in Saline-sodic Rice Areas

为探究秸秆还田对苏打盐碱稻田土壤水稳性团聚体组成、稳定性、各粒级团聚体有机碳分布以及产量的影响,以期为松嫩平原西部苏打盐碱地土壤改良及土壤团聚体固碳技术提供理论依据。试验于2017—2020年在吉林省大安市舍力镇苏打盐碱稻区进行,共设置5个处理,秸秆施用量分别为ck(0 t/hm^(2))、S_(1)(2.8 t/hm^(2))、S_(2)(4.2 t/hm^(2))、S_(3)(5.6 t/hm^(2))、S_(4)(7.0 t/hm^(2))。于2019年、2020年在水稻成熟后进行测产及采集土壤样品,测定土壤容重、土壤有机碳,利用湿筛法得到不同粒级土壤团聚体,测定各粒级团聚体有机碳含量。结果表明:与ck相比,S_(2),S_(3),S_(4)处理显著降低土壤容重。苏打盐碱土壤团聚体主要是以0.053~0.25 mm的微团聚体为主,秸秆还田显著降低了<0.053 mm团聚体占比;秸秆还田使土壤平均重量直径(MWD)和>0.25 mm粒级团聚体含量(R>0.25)提高,且随着秸秆还田量的增加而增加。秸秆处理显著提高土壤有机碳含量,与ck相比,2019年有机碳含量提高了18%~44%,2020年提高了27%~43%;秸秆还田增加了各个粒级团聚体有机碳含量,且降低了微团聚体(<0.053 mm)的有机碳贡献率,S_(1),S_(2),S_(3),S_(4)处理<0.053 mm团聚体有机碳贡献率2019年下降15.14%~43.93%,2020年下降23.42%~49.05%。秸秆还田显著增加苏打盐碱稻田的产量,且随着秸秆还田量的增加,水稻产量呈现先升高再降低的趋势,在S_(3)处理达到最大值,S_(3)处理2年产量分别为9.83 t/hm^(2)(2019年)和9.60 t/hm^(2)(2020年),比ck处理增加30%(2019年)和28%(2020年)。这说明秸秆还田不仅显著降低了土壤容重,显著提高土壤大团聚体(>0.25 mm)占比且增强团聚体稳定性,改善土壤物理结构;提高土壤有机碳含量,并提高大团聚体有机碳贡献率,提高土壤养分;可显著提高水稻产量。相比之下,S_(3)处理(5.6 t/hm^(2))为改善苏打盐碱稻区土壤结构和提高水稻产量的最佳秸秆还田量。

The study aims to investigate the effects of straw returning on composition and stability of water-stable agglomerates,distribution of organic carbon in agglomerates of different particle sizes and yield of saline-sodic rice paddies,in order to provide a theoretical basis for soil improvement and soil agglomerate carbon sequestration technology in saline-sodic soils in western Songnen plain.The experiment was conducted in 2017—2020 in the saline-sodic rice areas of Sheli town,Daan city,Jilin province,with five treatments,namely ck(0 t/hm^(2)),S_(1)(2.8 t/hm^(2)),S_(2)(4.2 t/hm^(2)),S_(3)(5.6 t/hm^(2))and S_(4)(7 t/hm^(2)).In 2019 and 2020,soil samples were collected after rice maturity to determine soil bulk density and soil organic carbon,and soil agglomerates of different particle sizes were obtained using wet sieve method to determine organic carbon content of each particle size agglomerate.The results showed that(1)S_(2),S_(3)and S_(4)treatments significantly reduced soil bulk density compared to ck.(2)Soda salty soil aggregates were mostly microaggregates of 0.053-0.25 mm,and straw returning reduced proportion of<0.053 mm aggregates considerably;straw returning increased mean weight diameter of soil(MWD)and content of agglomerates(R>0.25)at the>0.25 mm particle size,and it increased with the increase of straw returning amount.(3)Straw treatments improved soil organic carbon content considerably;compared to ck,organic carbon content rose by 18%to 44%in 2019 and 27%to 43%in 2020.(4)Straw returning increased organic carbon content of agglomerates of different particle sizes while lowering organic carbon contribution of microagglomerates(<0.053 mm),and contribution rate of organic carbon in<0.053 mm agglomerates treated with S_(1),S_(2),S_(3),and S_(4)decreased by 15.14%to 43.93%in 2019 and by 23.42%to 49.05%in 2020.(5)Straw returning significantly increased yield of saline-sodic rice paddies,and with the increase of straw returning,rice yield showed a first increasing and then decreasing trend,reaching a maximum in S_(3)treatment;the two-year production of S_(3)treatment was 9.83 t/hm^(2)(2019)and 9.60 t/hm^(2)(2020),respectively,which increased by 30%(2019)and 28%(2020)compared to ck treatment.The study indicates that straw returning not only significantly reduces soil bulk density,significantly increases proportion of large soil aggregates(>0.25 mm),enhances stability of aggregates,and improves soil physical structure,but it also increases content of soil organic carbon,and contribution rate of organic carbon to large aggregates,and improves soil nutrients,thus significantly increasing rice yield.In contrast,S_(3)treatment(5.6 t/hm^(2))is the best amount to improve soil structure and rice yield in the saline-sodic rice areas.