Water diffusivity of sandy soils of different particle sizes

Soil water movement parameters include its diffusivity,conductivity,and so on,which synthetically reflect the water retentively and movement capacity.It is absolutely necessary to research soil water movement regularity and to analyze soil water movement quantitatively with mathematical monitoring method.Unsaturated soil water diffusivity is an important hydraulic parameter for estimating irrigation quota,water infiltration and water loss.In this paper,water diffusivity of sandy soils of different particle sizes from typical sandy croplands are measured with the method of horizontal soil columns.The results show that the sequences of the wetting front advancement rates are 0.50-0.25 mm,0.25-0.10 mm,undisturbed soil and sand soil of 0.10 mm.The infiltration capability is positively correlated to soil particle size,the relationship between infiltration distance and the rate of wetting front advancement is fitted as a power function.With the increase of soil water content,Boltzmann parameter decreases gradually,for the sandy soil of 0.10mm,when soil water content less than 0.415,the Boltzmann parameter decreases slowly with soil water content increasing,when soil water content is more than 0.415,the Boltzmann parameter decreases rapidly.Water diffusivity decreases gradually with the decrease of soil particle size,the sequences of water diffusivity are 0.50-0.25 mm,undisturbed soil,0.25-0.10 mm and sand soil of 0.10mm.There is significant positive correlation between water diffusivity and soil water content,the relationship is consistent with a rule of exponential curve and conforms to the empirical equation.