Profile morphology and organic carbon distribution of saline-sodic soil in different rice planting years
Saline-sodic soil with different rice planting years was selected to study the effect of rice planting years on profile morphology of saline-sodic soil and the distribution and stability of organic carbon.Through field experiment,the uncultivated saline-sodic soil and the saline-sodic soil which were cultivated for 1 year,5 years,10 years,15 years,20 years and 40 years in the uncultivated were selected as the research object.The profile morphology,pH value,content of micro-aggregates,distribution characteristics of organic carbon in micro-aggregates and content of easily oxidized organic carbon were measured and analyzed.The results showed that compared with the uncultivated saline-sodic soil,the color darkness of the soil tillage layer was deepened with the increase of years.The soil in each section was mostly granular and prismatic.The soil resistance became loose.Both the uncultivated saline-sodic soil and the saline-sodic soil after planting rice had higher carbonate content,and the lime reaction degree was different in each profile.The pH value of each layer of saline-sodic soil was reduced at different degrees.Among the micro-aggregates,the content of large micro-aggregates with a grain size of 0.05 mm-0.25 mm was the greatest,and the grain size aggregates were decomposed into micro-aggregates<0.05 mm by rice planting.From 1 to 5 planting years,the organic carbon content in small micro-aggregates was increased,and from 10 to 40 planting years,the organic carbon concentrated in large micro-aggregates.The content of easily oxidized organic carbon of saline-sodic was promoted with the increase of rice planting years.Compared with the uncultivated saline-sodic soil,the oxidative stability coefficient of easily oxidized organic carbon in saline-sodic after rice planting was lower.The oxidation stability coefficients of tillage layer,subsurface layer and infiltration layer reached the minimum values at 40 years,15 years and 10 years of rice planting,respectively.In conclusion,long-term rice planting not only improved the structure of saline-sodic soil,its pH value and the stability of organic carbon,but also increased the content of small micro-aggregates and the organic carbon content of large micro-aggregates.
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