Black-soil paddy field experiment on improving soil physical and chemical properties and increasing rice yield by continuous deep ploughing

Abstract: Rice is cultivated in large area in Heilongjiang Province. The area of rice cultivation in Heilongjiang is about 100 thousand hectares. For a long time, rotary or shallow ploughing is the main tillage mode of paddy soil. Rotary tillage depth is usually 8-10 cm, and shallow ploughing is 12-13 cm. Long term shallow ploughing has the following problems. First, it makes plough pan layer move upward, which leads to the shallower tillage layer and the rise of the plow bottom. With the reduction of effective space for roots growth, roots cannot absorb nutrients from deep soil and the soil nutrient supply per unit area will decrease. Second, it easily leads to rice lodging in late growth stage due to the shallow rooting zone. When the roots are hindered by the plough pan layer, they cannot grow vertically and only extend horizontally, which results in a decrease in the ability to support stems. The more roots in the deep soil, the stronger the ability of roots to fix the soil, and the stronger lodging resistance. Shallow ploughing leads to a decrease in the soil nutrient supply per unit area. In order to meet the growth of crops, a large amount of fertilizers have to be applied, especially nitrogen, which can cause late maturing rice, lodging and losses in yield. Third, soil aeration and water permeability are impeded by the plow bottom, the air in the upper and lower soil layers is not in circulation. As long as the soil is in the reduction state, it is easy to form reduced iron, manganese as well as reduced gases such as H2S, which results in rice roots poisoning and a reduction of yield. The results of the survey for rice cultivation in Heilongjiang area showed that the topsoil thickness of high-yield cropland soil is generally 15-17 cm, and the plough layer thickness is 7-8 cm. the medium-yield cropland soil is generally 12-15 cm and 8-10 cm, and low-yield is 8-10 cm and greater than 8-10 cm, respectively. In Honghe farm, long term production practice concluded that the yield of 20 cm deep ploughing was 10% higher than that of 8-10 cm. In order to clarify the effects of deep ploughing on soil physical and chemical properties and rice yield, in this paper, we carried out the research of large area contrast of deep tillage, shallow tillage and rotary tillage by use of the independent developed deep plough of paddy field. The results showed that shallow and deep ploughing can reduce soil solid ratio and bulk density. The soil solid phase ratio was 0.74%-4.80% and 1.86%-3.90% lower than rotary tillage respectively. The soil bulk density respectively decreased by 0.09 g/cm3 and 0.08 g/cm3 in the 10-20 cm soil layer. The soil bulk density of deep ploughing was decreased by 0.03 g/cm3 than that of rotary tillage in the 20-30 cm soil layer. Compared with rotary tillage, the soil permeability coefficient and saturated permeability coefficient of shallow ploughing were increased by 4.04 and 2.71 times in the 10-20 cm soil layer, respectively, those of deep ploughing were 4.42 and 2.14 times, and those of deep ploughing were 1.86 and 2.87 times in the 20-30 cm soil layer. In two years, the change trend of soil aeration coefficient and saturated permeability coefficient was consistent. Deep ploughing can promote the growth of rice roots. The increase of root growth amount and length was 6.53%-16.33% and 10.81%-21.62%, respectively, and deep ploughing is better than shallow. Deep ploughing increases the yield of rice. In 2015, shallow and deep ploughing in rice yield increased by 6.91% and 9.81%, respectively compared with rotary tillage, and by 6.59% and 7.84% in 2016. The trend of increasing yield was consistent in two years.