Influencing Factors And Prediction Model On Red Soil Penetration Resistance

Seasonal drought is a key factor restricting the farming of the red soil area in South China. Red soil, as an high bulk density and clay particles contents, the penetration resistance of which will increase sharply if the soil water content decreases, and then affects the crop root elongation and water absorption. But there were little literatures studied on the status of the penetration resistance of red soil. And it is unknown that how strong the impact of soil properties on the penetration resistance. The objectives of this thesis were to study the change of soil penetration resistance with moisture content and the effect of soil properties, land utilization type and fertilizer treatments under different cultivation measures on the relationship between soil penetration resistance and moisture content, and compared different forms of resistance prediction model. From the results, some scientific basis was provided for discussing the formation mechanism of seasonal drought and defending the seasonal drought in red soil area.The laboratory experiment set up three bulk density (1.1,1.3,1.5g/cm3)simulating the process of field drought and monitoring the change of penetration resistance.The field experiment was carried out in the tea garden, woodland and the farmland area for monitoring the change of penetration resistance in root layer from June to September in2012. The farmland area set four fertilizer treatments, including no fertilizer-CK, application of chemical fertilizer-NPK, application of manure-PCM and application of chemical fertilizer with straw returning-NPKM. Each fertilization treatment set no-tillage and conventional cultivation measures. The red soil used in both methods was developed from parent materials of quaternary red clays and the crop in field experiment was summer maize. The instrument for measuring the soil penetration resistance were TYD-1micro-penetrometer (in pots) and SC900soil penetrometer (in fields). The main findings are showed as follows:The relationship between soil penetration resistance and water content was non-linear and negative correlation significantly. The penetration resistance mostly surpassed the maximum resistance suitable for the root (2.0MPa) in mild and moderate droughts. And it was unimodal distribution in soil layer of0～40cm. In moderate drought, the biggest resistance of tea garden was3.51MPa in the12.5cm layer and the woodland was4.78MPa in the5.0cm layer. The biggest resistance of CK with no-tillage was5.12MPa in the22.5cm layer and the NPKM with no-tillage was4.38MPa in the12.5cm layer. The biggest resistance of plots with conventional tillage (except NPK) were less than2.0MPa in soil layer of0-20cm. The difference of penetration resistance was significant among the plots of different land utilization types, cultivation measures and fertilizer treatments, and it enlarged as water content decreased. The result indicated that as for red soil, the penetration resistance increased sharply due to lowered water content.The properties of red soil affect the penetration resistance, but the bulk density, texture, organic matter had different influence on penetration resistance and the relationship between penetration resistance and water content. The influence of bulk density was most significant. When water content reduced to0.20g/g, the change of penetration resistance increased sharply. The texture and organic matter had significant influence on penetration resistance when water content was more than0.17g/g, and penetration resistance decreased with the increase of organic matter or silt content. With the reduction of the water content, the penetration resistance of each plots in soil layer of0～10cm increased significantly comparing to the other three soil layers. The difference of tea garden was significantly greater than woodland’s and NPKM had the least difference among the no-tillage plots. The penetration resistance of CK with conventional tillage increased as water content increased. The result indicated that high bulk density would lead to higher penetration resistance than other soil properties.This paper selected four models whose forms as below:Q=aθb(1), Q=aθbDc (2), Q=a|Ψ|b-c|Ψ|(3), log10Q=alog10|ΨS|+blog10D+c (4) simulating the penetration resistance of each experimental plots and Q is the penetration resistance (KPa),θ is the water content (g/g), D is bulk density (g/cm3), Ψ is matric potential (-KPa), S is the saturation of soil moisture (water content/field capacity), a、b、c are the model parameters. Different models had different performance on the penetration resistance prediction.We can select model4and model2for non-agricultural land and no-tillage agricultural land, respectively. For conventional tillage agricultural land, we can select the model2after the bulk density stabilized. The results can be used to predict red soil penetration resistance.