Evaluation of soil water retention pedotransfer functions for Vietnamese Mekong Delta soils

• The reliability of published PTFs for VMD soils varies according to PTFs’ calibrated data sets.
• PTFs derived from large databases of tropical soils perform better in estimating SWRC of VMD soils.
• Applicability index and geographical position can be used as indicators to select proper PTFs.
• Specific PTFs for tropical deltas soils should be developed to estimate accurately SWRC.

Appropriate management of irrigation and drainage, which require the information of soil water retention characteristics (SWRC), is of crucial importance for sustainable paddy rice production in tropical deltas. SWRC, however, is usually missing due to the lack of facilities, cost, and personnel training involved in direct measurement methods. Pedotransfer functions (PTFs) that provide the estimation of SWRC from other basic soil properties are the alternative source of SWRC for practical soil water managements or modeling purposes. Since developing new PTFs is a very arduous task which requires a large soil database of good quality, utilizing existing PTFs where possible is highly recommended. The objective of this study was therefore to evaluate the applicability and reliability of published SWRC-PTFs for soils in tropical Vietnamese Mekong Delta (VMD) where paddy rice is the main agricultural practice. A number of well-known statistical regression and pattern-recognition PTFs were selected for the evaluation. By assessing the correspondence between measured and PTF predicted values of SWRC, the results show that the PTFs derived from large databases of soils in the regions having similar climatological and pedological conditions to VMD soils are more reliable for predicting SWRC (RMSE varies in the range of 0.06–0.07 m3 m−3, and of 0.05–0.06 m3 m−3 for the prediction of soil water content at −33 kPa and −1500 kPa, respectively). The applicability index together with geographical information, therefore, could be used as integral indicators to select appropriate PTFs in cases no SWRC data are available for timely uses. Detailed evaluation of PTFs’ performance however revealed the limited potential of investigated PTFs to VMD soils. Further researches to develop specific PTFs for tropical delta soils are recommended for accurate SWRC estimation in such regions.