Simple model to estimate soil water retention limits of Chattisgarh state

Abstract

To know available water holding capacity of soil, knowledge of soil water retention limits is essential. This is useful in irrigation scheduling, water balance simulation and land use planning. The measured soil water limits: upper limit at field capacity (-33 kPa pressure) and lower limit at permanent wilting point (-1500 kPa pressure) was available for 67 established soil series of Chattisgarh state. In the present paper, a simple generic power equation has been developed to estimate the soil water limits based on soil survey data such as texture and bulk density. Linear regression was used to estimate the gravimetric soil water limits from sand and clay percentages. The volumetric soil water limits is estimated by multiplying gravimetric soil water limits with bulk density. The predictions were adjusted for coarse fragments and organic carbon present in the soil matrix.The standard error (SE) of the measured water content at field capacity (Wfc) and at permanent wilting point (Wpwp) are 0.98 and 0.54 respectively whereas the SE of the estimated water contents by the developed models are less, 0.89 and 0.51. The percentage error between the estimated and measured Wfc and Wpwp found to be 10.1 and 5.8 respectively Comparison made through graphical representation of error bars also shows satisfactory result at (i) ±1.96 (SE) and (ii) ±10% error criteria. Coefficient of variation (CV) also indicates improvements. The goodness of fit (R2) value between the estimated Wfc with measured Wfc, is 0.85, which shows model estimation is reasonable. Similarly, for values of Wpwp by model estimation R2 is 0.81. Paired „t‟ test for comparison shows that model is estimating well at 95% confidence level.