Effects Of Tillage And Straw Returning On Aggregate Composition And Organic Carbon Content Of Black Soil

Compared with other types of soil,black soil has better physical and chemical properties and is a valuable agricultural resource.Large scale reclamation and long-term high-intensity cultivation are the main reasons for the serious degradation of soil aggregation and the obvious decrease of organic carbon content in black soil,which seriously affect the sustainable development of agriculture in Northeast,and thus threaten the food security of China.As important part of conservation tillage,no tillage and straw returning can improve physical and chemical properties of soil more effectively than conventional tillage.At the same time,applying straw to farmland can also avoid various environmental problems caused by burning straw.Soil aggregation and organic carbon content are important soil quality evaluation indices.They play important roles in guiding agriculture and ensuring food production safety.In order to explore the protection and enhancement effect of no tillage and straw returning on soil aggregation and organic carbon content of black soil,an experiment was carried out in Xiangyang experimental base of Northeast Agricultural University in Harbin since 2015.Four treatments including straw returning with no tillage(NTS),no tillage(NT),straw returning with conventional tillage(CTS)and conventional tilliage(CT)were designed.Soil samples were collected in 2018 and 2019.The soil aggregation,organic carbon content of soil and organic carbon content of aggregate at 0-10,10-20 and 20-30 cm soil layers were measured and calculated.The impact of no tillage and straw returning on the physical and chemical properties of soil was analyzed to provide theoretical guidance for the sustainable utilization of black soil in Northeast China.The main results were as follow:(1)Effect on soil aggregation: In 0-10,10-20 and 20-30 cm soil layers of 2018 and 2019.The percentage content of water-stable aggregate larger than 5 mm,Mean Weight Diameter(MWD)and Geometric Mean Diameter(GMD)of NTS and NT treatments were significantly higher than those in CTS and CT treatments.The fractal dimension and percentage content of water-stable aggregate smaller than 0.25 mm of NTS and NT treatments were significantly lower than those in CTS and CT treatments.No tillage and straw returning were beneficial to the formation of soil macroaggregate,while the percentage of soil microaggregate decreased,made Mean Weight Diameter and Geometric Mean Diameter of aggregate increased,the fractal dimension of aggregate decreased,the stability of aggregate increased.Compared with the other three treatments,NTS treatment could maintain the soil structure better.(2)Effect on soil organic carbon content: In 0-10,10-20 and 20-30 cm soil layers of 2018 and2019,the soil organic carbon content of NTS and NT treatments were significantly higher than those in CTS and CT treatments.The organic carbon content of each treatments showed an overall decreasing trend with the increase of soil depth.The soil organic carbon content of each treatments ranged from 7.62 g/kg to 11.66 g/kg in 2018,ranged from 7.67 g/kg to 12.18 g/kg in 2019,the soil organic carbon content in 2019 was higher than that in 2018 totally.No tillage was beneficial to the increase of the organic carbon content of the soil,straw returning had no significant effect on organic carbon content of the soil,and the organic carbon stratification rate of NTS was higher than that of the other three treatments.(3)Effect on organic carbon content in aggregate: In 0-10 cm soil layer of 2018 and 2019,the organic carbon content in aggregates of NTS and NT treatments were significantly higher than those in CTS and CT treatments.The organic carbon content in aggregate of each treatments showed an overall decreasing trend with the increase of soil depth.The peak value of organic carbon content in aggregate appeared at 1-2 mm.The organic carbon content of macroaggregate was higher than that of microaggregate.No tillage and straw returning were beneficial to the increase of organic carbon content in aggregate.(4)Effect on organic carbon contribution rate of aggregate: In 0-10,10-20 and 20-30 cm soil layers of 2018 and 2019,the organic carbon contribution rate of water-stable aggregates of larger than 5,2-5 and 1-2 mm of NTS and NT treatments were higher than those in CTS and CT treatments generally,and those of water-stable aggregate smaller than 0.25 mm was smaller than that of CTS and CT treatments.In the same treatment,the contribution rate of organic carbon of water-stable aggregate smaller than 0.25 mm was always the largest.(5)Effect on maize yield: The maize yield of each treatment in 2019 was significantly lower than that in 2018,and there was no significant difference between each treatments in 2018 and2019.After four years of continuous cultivation,no tillage and straw returning had no significant effect on maize yield.(6)The results of correlation analysis showed that the percentage of water-stable aggregate larger than 5 mm had a significant positive correlation with the MWD and GMD values of aggregate,and a significant negative correlation with the fractal dimension.The organic carbon content of soil was significantly positively correlated with the percentage of aggregate larger than5 mm,MWD and GMD,negatively correlated with the fractal dimension.The content of organic carbon of different aggregates were positively correlated with the organic carbon content of soil.Comprehensive analysis of soil physical and chemical properties showed that no tillage +straw returning treatment could improve and enhance soil aggregation,soil organic carbon content and aggregate organic carbon content,which was conducive to the sustainable utilization of black soil in Northeast China and food production security.