Developing a new subsoling method is one of the important ways to improve the subsoiling efficiency and overcome the traditional subsoling weakness, i.e. limited range and inhomogeneity. The present paper proposed a noval subsoiling method based on pneumatic split technology, namely, air pressure subsoiling. During the air pressure subsoiling, air was injected into cultivated soil to result in plenty of cracks inside the soil. In order to investigate the effect of air pressure subsoiling, a simulation experiment was carried out to observe the inner and external changes of soil before and after air pressure subsoiling with 3 indices including soil porosity, soil porosity increasing rate and soil surface uplift. Experiment was carried out from December 10, 2014 to February 10, 2015 in the Agricultural Machinery Laboratory of the Engineering Research Center of Northeast Agricultural University. Test and research methods were as follows: 1) Firstly, the Miller Soil Box test equipment was used to test soil resistivity of different moisture content, porosity and saturation of black cultivated soil in the Northeast of China. The various parameters of Archie soil resistivity model were formed based on the regression analysis of our test result. Then a regression formula was acquired to calculate soil porosity by soil resistivity and soil moisture content acquired. 2) According to the actual cultivated land status of subsoiling in the Northeast of China, the plough layer and plow pan were made. The procedure was that 0.2 m plow pan was set on the groove bottom at first, and then 0.2 m plough layer was covered, which had 1.17 g/cm3 bulk density and 18% moisture. Two factors and 3 levels (plow pan bulk density of 1.4, 1.6 and 1.8 g/cm3, and subsoiling air pressure of 1.4, 1.6 and 2.2 MPa) were set in the experiment. Our experiment used the self-made air pressure subsoiling equipment to inject air into the plow pan with different bulk density (0.35 m deep), before and after air pressure subsoiling, used the regression formula to calculate the soil porosity and its increasing rate before and after air pressure subsoiling, and at the same time measured the vertical rise of soil surface when measuring the soil resistivity. 3) Draw contour map of soil resistivity, soil resistivity increasing rate and vertical rise by the Origin software in order to analyze the distributions and changes of soil resistivity, soil resistivity increasing rate and vertical rise before and after subsoiling. Further more, we compared air pressure subsoiling with 3 traditional subsoilers (triangle shovel, arrow shovel and chisel shovel) on the effect of subsoiling by analyzing the scope of subsoiling, uneven extent and soil porosity increasing rate. Main results obtained were as follows: 1) The regression formula of subsoiling soil porosity, soil resistivity and moisture content was obtained, which was suitable for the black soil in the Northeast of China. 2) For the plow pan with bulk density of 1.4, 1.6 and 1.8 g/cm3, when subsoiling air pressure was 1.4, 1.6 and 2.2 MPa, air pressure mainly formed horizontal cracks which resulted in an obvious increase of soil porosity. These cracks could effectively break the plow pan, increase the air content in the soil after subsoiling, make the soil volume expand and the surface uplift. Excellent subsoiling could be obtained with fewer changes or effects for plough layer. 3) Compared with traditional subsoiling, air pressure subsoiling had the merits of larger scope, more uniformity and higher efficiency. For the effectively influenced radius on land surface, air pressure subsoiling was about 2~2.5 times of traditional subsoiling, and it was at least 3 times of traditional subsoiling on plow pan. The results and the data obtained in this paper can provide a reference for the further study and the design of air pressure subsoiling equipment. © 2016, Chinese Society of Agricultural Engineering. All right reserved.
