A simple method to determine soil moisture regime for highly weathered tropical soils

Introduction. The soil water balance approach can be used to evaluate soil water dynamics and determine soil moisture regime (SMR) and water availability. Despite some models are available in the literature, they have been validated within temperate regions, and require several input variables, restringing their use when data is limited. Objective. To develop a simple method to estimate soil water balance (after infiltration) and further determine the corresponding SMR for highly weathered soils from Costa Rica, Central America. Materials and methods. Twelve pedons (distributed in seven regions of Costa Rica) were sampled and described, where monthly total soil available water (TSAW) and available water in the soil control section (AWCS) were calculated. Potential evapotranspiration (ETo) and monthly dependable precipitation (DP) were estimated using historical data obtained from neighboring meteorological stations. DP, ETo, TSAW, and AWCS were used as variables in the calculations performed to identify months with soil water deficit. Results. Three SMRs were identified: 1) Ustic (six pedons), 2) Udic (four pedons), and 3) Perudic (two pedons). In five assessed pedons, SMR assigned through our soil water balance approach disagreed with that reported in the literature for nearby areas (SMR estimated through Newhall model). However, historical rainfall behavior and the developing crops and vegetation in these regions reinforced the SMR assigned to this research. Conclusions. The method developed in the present study was considered satisfactory in determining both soil available water and SMR for highly weathered soils of Costa Rica. We encourage its use in further studies of hydrology, soil physics, and pedology due to 1) its versatility of use with limited data and 2) the inclusion of meteorological and edaphic variables calibrated under tropical conditions