Effect on improving mollisol paddy soil and saline meadow soil by continuous deep ploughing

Abstract: Heilongjiang province is the main production area of Japonica Rice in China. In Heilongjiang Province, rice growing areas are mainly distributed along Rivers and low plains. Due to the short time of planting rice, the development of paddy soil, which still keeps the original soil characteristics, is not completed. Rotary tillage is the main way of soil preparation in spring. Tillage depth is persistently maintained at 8-12 cm in paddy soil, which results in thin tillage layer, shallow plough bottom, and restricts rice root extension. With the decrease of soil holding capacity, rice plants prone to lodging at the later stage of growth, and rice yield and quality are affected. When the tillage layer is thin, the soil nutrient capacity is low, and the natural fertility is restricted, it is often used to increase the yield of rice by adding chemical fertilizer. The increase in the amount of fertilizer is not only a waste of fertilizer, but also pollutes the environment. The experimental results of the Honghe farm in the Sanjiang plain showed that, with the increase of paddy field tillage depth from 10 cm to 15 cm, the yield increased by about 10%. Japanese statistics showed that the thickness of the plough layer was more than 16-18 cm, some of which were more than 20 cm. The yield of rice was closely related to the thickness of topsoil. At present, there is no clear conclusion about the suitable depth of soil in different types of paddy soils in Heilongjiang Province.In order to clarify the effect of deep tillage on different types of paddy soils, the experiment , using the self-developed paddy deep plough, was carried out to study the effects of deep ploughing, shallow ploughing and rotary tillage in black soil and salinized meadow soil. Results showed that the effects of deep tillage on rice yield and soil physical and chemical properties were different. First, black soil deep ploughing treatment increased yield by 7.28%-8.37%. there was no significant difference in grain yield between the deep ploughing and rotary tillage treatment of salinized meadow soil in first years, but in the second year rice yield decreased by 9.96%-11.03%. Second, plowing promoted the homogenization of soil nutrients in black soil, and the soil nutrient content was not significantly reduced, and the difference of nutrient content between soil layers became smaller. Deep tillage caused the decrease of nutrient concentration in salinized meadow soil. The soil organic matter content of the shallow and deep ploughing treatments respectively decreased by 4.57 and 6.68 mg/kg compared with the control in 0-20 cm layer of salinized meadow soil, and total nitrogen decreased by 0.24 and 0.29 g/kg. The alkali hydrolyzable nitrogen in 0-10 cm soil layer of the kind of soil respectively decreased by 2.31 and 11.52 mg/kg, and pH value increased significantly, and the exchangeable Na+ concentration increased in the 0-30 cm soil layer. Third, compared with the control, the shallow and deep ploughing decreased the solid ratio and bulk density of black soil, and increased soil aeration and water permeability. The soil solid ratio of 10-20 cm soil layer was decreased by 4.23% and 3.23%, respectively. The soil bulk density was decreased by 0.09 and 0.08 g/cm3, and the ventilation coefficient increased by 3.04 times and 3.42 times, and the permeability coefficient increased by 1.71 times and 1.14 times, respectively. The soil solid phase ratio of deep ploughing treatment in the 10-20 cm soil layer of black soil was reduced by 1.86%, and the ventilation coefficient and saturated permeability coefficient increased by 0.86 times and 1.87 times. Fourth, there was a tendency to increase the subsoil solid and bulk density and reduce the ventilation and permeability of salinized meadow soil in the shallow and deep ploughing areas. Deep tillage is not suitable for salinized meadow soil, the effect is obvious in black soil, deep tillage can improve soil physical and chemical characteristics and increasing yield.