Accumulation and replacement of exchangeable sodium in soils of Southeast Texas under turfgrass and its effect on soil infiltration rate

Abstract

Many municipal water supplies in Southeast Texas have a relatively high level of Ne and low total dissolved solids. Smectitic clays which respond to wetting by swelling, especially when wetted with high Na waters of low salinity are the major clays in soils of this area. This study assessed the degree of Na accumulation on cation exchange sites as affected by gypsum treatments in soils that support turfgrass (bermudagrass) and the response of soil infiltration rate to different rates of gypsum amendment by using rainfall simulation. A field experiment was conducted on a sodic, non-saline Boonville soil (fine, montmorillonitic, thennic Ruptic Vertic Albaqualf) amended with gypsum at rates equivalent to 5 0%, I 00% and 200% of the exchangeable Na in the soil to a depth of 15 cm. Application of gypsum resulted in similar infiltration rates (IR) which were lower than the untreated plots suggesting a significant difference between treated and untreated soils 9 wk after application. However, at 36 wk after application, treated and untreated soils had similar IR with no statistical difference between treatments. Soils of the study area varied somewhat in textural class, but generally had more than 20 % clay within the 0-IO cm depth. Clay content in the 0-10 cm depth was not correlated with IR at the 20-min measurement. These results suggest the channels developed by roots may enable water to enter the soil in spite of clay content and degree of sodic character. The gypsum treatments statistically affected the levels of extractable Ca and Na in some plots and some depths. Treated plots had higher extractable Ca than untreated plots for the 01 0 cm depth for all sites, but treatment rates did not show a significant difference for each site in the same depth. Levels of extractable Na were statistically lower for treated plots than untreated ones for the 0-I 0 cm depth at all sites. For all sites gypsum application did not have significant effects on levels of extractable Mg and K at all depths and times. Even though the pH of the soils tended to decrease with application of gypsum, untreated soils also showed a decrease in pH over the course of the study and pH was not statistically significant.