Effect of soil pore size distribution on plant-available water and least limiting water range as soil physical quality indicators

Soil pore size distribution (SPSD) is one of the most important soil physical properties. This research investigated the relationships of location and shape parameters of the SPSD curves with plant-available water (PAW) and least limiting water range (LLWR) of the light-textured soils at the Torogh Agricultural Research Station in north-eastern Iran. Soil moisture release curve (SMRC), PAW and LLWR in matric heads of 100 and 330 hPa for the field capacity and location and shape parameters of the SPSD curves of 30 soils with different texture and organic carbon contents were determined, and the variable relationships were statistically analyzed. The results showed that the median equivalent pore diameter (d(e)), mean de, standard deviation (SD*), and skewness of the SPSD curves were significantly correlated with PAW (PAW(330)) and LLWR (LLWR330) measured in a matric head of 330 hPa. Decrease in d(e) and increase in the diversity of soil pore size (SD*) increased PAW(330) and LLWR330. The SD* values of all the soil samples were lower than the optimal ranges suggested in literature. Neither PAW nor LLWR values were significantly different in the soils with the optimal modal de and those with non-optimal modal d(e). Optimal values of median and mean equivalent pore diameters and kurtosis of SPSD curves led to a significant improvement of PAW(330) and LLWR330 as soil physical quality indicators. It was recommended to revise the optimal ranges for SD* and modal de for future studies.