Effect of gypsum and biochar amendments on groundnut(Arachis hypogaea L.)biomass yield and selected soil properties under water stress

Abstract

Poor rainfall distribution, low soil calcium, soil acidity and low soil moisture stress contribute largely to low levels of groundnut productivity. Because the majority of groundnut farmers in Zambia are small-holder and have limited resources, they are not able to cope with these production constraints. A greenhouse pot experiment was setup at the University of Zambia during the 2016/2017 cropping season to assess the effect of gypsum and biochar soil amendments on biomass yield and soil properties under water stress. Msekera Groundnut Variety 5 (MGV 5) was planted in an acid sandy loam soil, classified in World Reference Base as a Chromic Luvisol, low in calcium. The experiment was laid out as a split-split plot experimental design with treatments consisting of gypsum (CaSO4.2H2O), groundnut shell biochar and plant water application rates as the main, sub-plot and sub-sub-plots, respectively. Four levels of biochar (0, 1, 2 and 4 % w/w of soil), two gypsum application rates (0 and 200 kg/ha) and three daily plant water application rates (100, 70 and 40 % plant water requirement (PWR)) were combined, giving a total of 24 treatment combinations. Soil reaction (pH), cation exchange capacity (CEC), leaf chlorophyll concentration index (CCI), biomass dry matter (DM), water use efficiency (WUE), crop evapotranspiration (ETc) were determined during crop growth or at the end of the experiment. Applying biochar had a neutralizing effect on the acid soil as it significantly raised the soil pH from 5 to 7.15 and increased the CEC by 75 %. Biochar also significantly increased the CCI at vegetative (V3) and reproductive (R1 & R3) stages of groundnut growth by 42, 46 and 40 %, respectively. Biochar at 1 and 2 % increased the dry biomass and ETc, by 28 and 13 %, respectively while at 4 % both were negatively affected. The optimum biochar application rate in this soil for biomass was at 1.42 % w/w. Biochar at 1 and 2 % had no effect on WUE while 4 % biochar reduced the WUE by 45 %. With a reduction in plant water application rate WUE and ETc also reduced by 50 and 35 %, respectively while the CCI increased by 22 %. Applying 100 % PWR gave biomass yields of 2 and 3-fold greater than at 70 % and 40 % PWR. Gypsum at a rate of 200 kg/ha had no significant effect on the crop, while biochar had potential to raise the soil pH, increase moisture retention and improve crop performance. Key words: biochar, biomass, crop evapotranspiration, groundnut, gypsum, water use efficiency