DSSAT-CSM Soil Module: Modeling Topsoil Water Holding Capacity in the two Dry Savanna
Zones of Kano State, Nigeria.
The objective of this study was to test the efficiency of the Hydraulic Pedotrans- fer Functions (PTFs) employed in the Decision Support System for Agrotechnol- ogy Transfer – Crop Simulation Model (DSSAT-CSM) in modeling topsoil WHC in Northern Guinea Savanna (NGS) and Sudan Savanna (SS) of Kano State in Nigeria. Coefficient of determination (R2), Root Mean Squared Error (RMSE), and Index of Agreement (d-index) were the three statistical methods used to test the fitness between predicted, and laboratory observed WHC of dis- turbed, auger sampled topsoil. Findings of the study established that the PTFs fitted in the algorithm of DSSAT-CSM soil water sub module made a significant topsoil WHC estimation in NGS with statistics R² = 0.352, RMSE = 0.03, and d- Index = 0.71. However, the model did not estimate the WHC validly in Sudan Savanna, with insignificant statistics of R² = 0.031, RMSE of 0.10, and 0.44 as the index of agreement. The conclusion drawn was that DSSAT made fair and poor predictions of topsoil WHC in NGS and SS soils respectively, irrespective of texture and other intrinsic properties. Based on the findings above, we recom- mend the development of local PTFs alternatives to be used with DSSAT’s algo- rithm for Nigerian Savanna soil