Improved understanding of soil water content at field capacity and estimates from pedotransfer functions

Abstract

The soil water content at field capacity, θFC, is a fundamental variable for irrigation and agriculture. This study determines the optimal tension ( 33 or 10 kPa) of deriving θFC which best matches the in situ field measurements following the Veihmeyer procedure. The Veihmeyer method refers to a profile water status for which there is a negligible drainage rate of bare soil without evaporation. In addition, we derive a set of linear and nonlinear pedotransfer functions (PTFs) which estimate θFC. θFC was measured in 69 plots in northwestern Iran, which has a cold semi-arid climate. The soil properties used for developing PTFs include texture, bulk density, and organic matter. The results show that θFC cannot be derived at a fixed tension. We therefore developed PTFs with satisfactory performance in reproducing in situ measured θFC. The findings show that PTFs developed at a fixed tension consistently underestimate θFC derived in situ. It was also speculated that tension less than 10 kPa could yield improved predictions of in situ θFC