Comparative effects of chemical amendments on salt and NA leaching

Abstract

Efficiency of sodic soil reclamation is thought to vary with types of chemicals used. This study examined the effects of five inorganic (H2SO4, CaCl2 · 2H2O, CaSO4 · 2H2O, FeSO4, Al2(SO4)3) and two organic compounds (polyacrylamide, and trihydroxy glutaric acid) on the rate and the extent of salt and Na leaching in moderately Na-affected saline soils: Saneli silty clay loam (Vertic Torrifluvents, ESP=17.5%) and Glendale silty clay (Typic Torrifluvents, ESP=13.5%). Air-dry soil samples (<2mm) were packed in columns, and chemicals, except H2SO4, were incorporated into the surface 5 cm of the soils, and in selected cases, to 30 cm. H2SO4 was surface-applied. Application rates of the inorganic chemicals were 3.57 and 10.7 mmol(+) kg-1 (2.5 and 7.5 Mg ha-1 in gypsum equivalent weight) in the silty clay loam, and 8 and 24 mmol(+) kg-1 in the silty clay, and the organic compounds were applied at rates of less than 620 kg ha-1. The soils were then leached with simulated Rio Grande water (EC = 1.1 dS m-1, SAR = 3.5) under continuous ponding. The tested inorganic compounds removed approximately equivalent amounts of exchangeable Na after approximately 35 cm of water application. However, the rate of water percolation (consequently the rate of salt leaching) from CaCl2 treated columns, became progressively slow after about 20 cm of water intake. The combined effect of rapid electrolyte leaching and insufficient replacement of Na in the surface layer seemed to be responsible for the flow reduction. Gypsum and H2SO4 treatments provided lower ratios of sodicity to salinity in percolating solutions and relatively uniform hydraulic gradients throughout the soil depth. Incorporation of chemicals to the surface 30 cm did not alter performance, except in CaCl2 treatments where water intake rates became even slower. The tested organic amendments improved initial water infiltration, but neither increased subsequent percolation rates nor improved salt and Na leaching. The fastest reclamation may be attained when chemicals are chosen and applied to yield an electrolyte concentration that is high enough to overcome Na effects at any depth of soil profiles throughout the leaching period.