Effect of planosol improvement by using straw subsoil mixed layer plough

Abstract: The subsoil of planosol is usually extremely hard, compacted and poorly nutrient during the growing stage of upland crops. These unreasonable physical-chemical properties of the subsoil trigger the problems on its topsoil, which makes upland crops frequently suffer dry and wet damage so called the surface dry and surface wet damage. Meanwhile it also functions as an obstacle layer limiting root extension, and hence the effective layer of root system of planosol is only about 20 cm. The research formerly carried out has proved that it could cease the problems of subsoil when the Aw (planosol layer) horizon and the B horizon (illuvia horizon) were mixed with the ratio of 1:1 while leaving the topsoil undisturbed. Through this method, the permeability and the water storage capability of the subsoil were increased. As a result, the machine named the three-stage subsoil mixing plough was developed. Since its working is deeper more than 50 cm, the plough provides the opportunity to return stalks into the mixed subsoil, and the poor nutrient condition of the subsoil can be therefore improved. Based on such kind of principle of planosol improvement, the machine so called the stalk-subsoil mixing plough was developed. This machine can make it come truth to leave the Ap (topsoil) horizon in depth of 20 cm undisturbed, while mixing the subsoil and stalk in depth of 30-40 cm. In this study, the large-size field tests were carried out with the stalk-subsoil mixing plough and the conventional plough at the 854 State Farm of the Sanjiang Plain, Heilongjiang Province of China. The physical-chemical properties after the machine operation were investigated. The agronomic characteristics and yield of the indicating crops were checked. The results showed that compared with the conventional plough, the stalk-subsoil mixing plough could significantly improve the soil physical properties. In the depth of ＞20-40 cm, soil moisture was increased by 2.69-4.90 percent points; soil hardness was reduced by 44.45%, and there was no hardness peak appearing. In 2014 and 2015, it also could improve soil permeability; solid phase was reduced by 4.51 to 2.14 percent points, water phase was increased by 1.17 to 4.31 percent points, air phase was increased by 0.38 to 0.98 percent points, and soil bulk density was decreased by 0.11-0.16 g/cm3. The soil chemical properties were also improved. In the depth where subsoil was mixed with stalks, available nitrogen (N) was increased by17.33%, available phosphorus (P) was increased by 116.39%, available potassium (K) was increased by 37.86%, and organic matter was increased by 36.66%. By the way, soil total N, P, and K and soil pH value were increased. During the 2 years the soybean yield in the field operated by the stalk-subsoil mixing plough was increased by 15.77%-16.33% compared with the field operated by the conventional plough. Thus long term effect for Planosol improvement can be achieved by using the technique of returning stalks.