Use of pedotransfer functions in crop growth simulation Utilisation de fonctions de pédotransfert dans la simulation de la croissance des cultures

Under water limiting situations, estimates of four critical parameters are required as inputs for integral simulation models, for predicting crop growth and yield. These are the soil water content values at saturation, field capacity, wilting point and air dryness. For many locations actual measurements are generally not available. Soil survey data routinely provides layerwise distribution of the textural components, organic carbon content and bulk density values. Simple relationships have been developed between the easily available or measurable soil properties routinely reported in literature and the four critical soil water constants. The data was collected from various sources representing the various agro-ecological regions of the country. Soil water content at saturation and wilting point were significantly correlated and satisfactorily estimated using clay content. Field capacity was negatively correlated and satisfactorily estimated using the sand content. The difference in R 2 using all the variables viz., sand, silt, clay, organic carbon content and bulk density, together and the properties taken individually, was generally less than two per cent. Hygroscopic coefficient values were assumed to represent the air dry moisture and could be estimated sufficiently accurately by using the clay content. The predicted values were very close to the estimated with the correlation coefficient (r) significant at P=0.01 for individual parameters. It was shown that the four soil water constants estimated by these simple relationships for 20 randomly selected soils were also very close to the observed values (R 2 =0.9472). The saturated hydraulic conductivity was negatively but significantly correlated with clay content but not as satisfactorily as the other soil water constants.