Abstract

The effects of amending soil with gypsum and biochar on groundnut chlorophyll concentration, water use efficiency (WUE), biomass yield and selected soil properties were investigated under water stress. Gypsum (CaSO4.2H2O) was applied at 0 and 200 kg/ha, groundnut shell biochar at 1, 2 and 4% w/w of soil, and water at 100, 70 and 40% of daily plant water requirement (PWR) as main, sub and sub-sub plots, respectively, in a split-split-plot design. Biochar neutralized the acid soil, significantly raising soil pH from 5 to 7.15 and increasing cation exchange capacity by 75%. Biochar amended at 1 and 2%, increased groundnut dry matter yield by 28%. The optimum biochar application rate for dry matter yield was 1.4% w/w. Biochar application at 4% and irrigation at 40% of PWR reduced the WUE by 45 and 50%, respectively. Chlorophyll concentration index was highest at 40% of PWR. The results suggest that biochar has potential to raise soil pH, increase moisture retention and improve crop performance.  Applying water at 100% PWR can increase groundnut dry matter yields, while higher gypsum application rates may be required to affect crop performance.

Key words: Biochar, dry matter, crop evapotranspiration, groundnut gypsum, water use efficiency.