Experimental Study On The Pressure Of Roots System On Soil

The pressure of roots system on soil is the pressure generated by the root system, which is produced by roots interspersing and increasing of root diameter during they are mechanical growing in the soil. With the growing of root, the pores of the soil displaced, which leads to the soil particles migration and the structural change, also leading to soil physical properties have changed, thereby affecting the migration of the soil bulk density, porosity characteristics and water or nutrients of soil. The pressure of root system on soil is a synthetically mechanical index of reflecting the roots-soil composite system. It's research belongs to biomechanics, at present, the mechanical effect of roots to the soil has not been systemic reported in the documentation at domestic and foreign, The analysis and research of the mechanical pressure of the root system, not only to promote the integration between the mechanical and agricultural cultivation, as well as the subject of soil erosion and promote the development of biomechanics, but also deepen the knowledge and understanding of the mechanical characteristics of the roots-soil composite system.Based on the theoretical analysis and model simulation calculation, by using the root system simulating experiments and the cultivation experiments, we analyzed the pressure range and vertical distribution characteristic of the pressure of root system on soil in the soil surface layer, and related the influence factors and there relationships. we established the equation between the pressure and the root system characteristic, a preliminary analysis of the pressure characteristic during plant growth also obtained, and the model of root pressure on soil was evaluated and modified. The main results are as follows:(1)The distribution of the pressure of root system on soil is between 2.5 to 4.2kPa during the 0~45cm soil layer. Pressure of the corn, wheat and other herb root system is between 2.0 to 2.7 kPa.(2)The distributed proportion of root system is less influence on the pressure of root. The relevance is not significant between the values of the pressure and the types of the plants when the diameter is smaller than 1mm, but when the diameter is larger, this similarity is not significant. The root system is a mechanics material which is vitality, when the diameter of the roots occurred the remarkable change, the variation of the pressure of roots system is more obvious, the diameter of the roots become larger is the main reason for the increase of the pressure of roots. As the soil deepens, the differences between their own roots have less influence on the mechanical pressure of roots compared with the force of volume around the soil.(3)To establish the indicators between roots characteristics and the pressure of roots, the relevance between the selected indicators and the pressure in this chapter is: the diameter of roots>the biomass of roots>the length of roots>the total surface area of roots. The diameter of roots is the best when select the indicators.(4) A new apparatus, which can measure the pressure of roots system on soil, is designed and manufactured. The experimental data measured using the new apparatus with the air-medium and liquid-medium are obtained. The new apparatus with the liquid-medium can also reached the demands of a experiment for measure the pressure of roots system on soil during the Plant Growing Period. It is shown by the experimental data measured using this new apparatus is suitable to measure the pressure of roots system on soil with high accuracy.(5) Simulation experiments show that: root diameter, the depth of root in the soil, soil bulk density and the wind on plant have significant impact on the pressure of root system, the pressure of root system increases in the form of power function as the roots diameter goes up, in the form of exponential function as the soil bulk density increasing, the pressure significantly increases as the soil layer becomes deeper, the pressure distribution in different soil layers is also related to the diameter of roots. The pressure has a significant relationship with the wind, increasing as the wind increase. This study built the multiple regression equation of the mechanical pressure (P) of root system between the diameter of roots (D) and soil bulk density(d): P=0.5918D1.4594ebd.(6)Using theoretical model, there is goodness of fit on a certain degree when calculated the plants which the diameter of roots is less than 2mm. It is more suitable when Poisson ratio is 0.28 to calculate the value of the pressure for the herbaceous-soil composite system.