The long-term effects of lime (CaCO3), gypsum (CaSO4.2H2O), and tillage on the physical and chemical properties of a sodic red-brown earth

In 1994 a long-term field trial with 9 lime-gypsum combinations and 2 tillage treatments (reduced tillage and direct drill) was established on a sodic red-brown earth soil [surface pH( water) 6.5] at a property near Peak Hill, NSW, Australia. The lime-gypsum treatments were: L0G0 (lime 0 t/ha, gypsum 0 t/ha), L0G1, L0G2.5, L0G5, L1G0, L2.5G0, L5G0, L1G1, and L2.5G1. After 3 years, higher rates of lime and gypsum or their combinations significantly (P<0.01) increased exchangeable and soluble calcium and decreased exchangeable and soluble sodium in the 0-100 mm layer of the soil. Gypsum was found to decrease the total soluble cation concentration (TCC) in some instances, while lime maintained TCC at 1995 levels. Soil pH was significantly higher on all lime plots and electrical conductivity was slightly higher on plots treated with lime than on control plots. Organic carbon levels were significantly higher in plots with gypsum and high levels of the lime-gypsum combination (L2.5G1). The effectiveness of the lime treatments was influenced by the initial soil pH (as suggested by the findings of other studies). The lime, and to a lesser extent the gypsum treatments, improved the physical properties of the soil as measured by the Emerson aggregate test, penetrometer resistance, infiltration, and water availability. A tillage effect was also present resulting in less dispersion, decreased penetrometer resistance, and higher infiltration rates in plots prepared with reduced tillage practices than direct drill plots. Plant-available water content (AWC) was significantly higher in the surface soil of plots treated with L2.5G1 than control treatments. The L5G0 and L0G5 treatments did not significantly improve the AWC. Crop yields were increased by some of the lime-gypsum treatments in both 1995 and 1996. Corresponding with the increased AWC, the L2.5G1 treatment produced the highest crop yields. Plots with reduced tillage had consistently higher yields than those with direct drill treatment.