1. College of Agronomy， Jilin Agricultural University， Changchun 130118， China；2. Key Labora?
tory of Germplasm Innovation and Physiological Ecology of Coldland Grain Crops， Ministry of Educa?
tion，Harbin 150030， China
Abstract：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/hm2), S1 (2.8 t/hm2), S2 (4.2 t/hm2), S3 (5.6 t/hm2) and S4 (7 t/hm2). 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) S2, S3 and S4 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 re?duced 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 S1, S2, S3, and S4 de?
creased by 15.14% to 43.93% in 2019 and by 23.42% to 49.05% in 2020. (5) Straw returning signifi?
cantly 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 S3 treatment; the
two-year production of S3 treatment was 9.83 t/hm2 (2019) and 9.60 t/hm2 (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 ag?
gregates, and improves soil nutrients, thus significantly increasing rice yield. In contrast, S3 treatment
(5.6 t/hm2) is the best amount to improve soil structure and rice yield in the saline-sodic rice areas.
