Impact of Biochar and Hydrogel Amendments on Hydrophysical Properties of Sandy Soil and Cowpea Yield (Vigna unguiculata L.) Under Different Water Regimes

Abstract

South Mediterranean countries including Egypt and Tunisia are characterized by vast lands with uncultivated sandy soils. These soils have poor hydrophysical-bio-chemical properties that are being reclaimed due to population growth and the need to increase food supply. Furthermore, there is high production of crop and orchard residues from agricultural activities that lead to harmful effects to the environment. Therefore, converting these residues to biochar and their use as amendments with sandy soils could improve water retention. This research investigated the effect of three soil amendments: - biochar (50 g/plant and 100 g/plant), hydrogel (2.7 g/plant) and their mixtures (hydro-char) (50 g biochar and 2.7 g hydrogel) on some hydrophysical properties. The properties included soil water constants, pore size distribution and void ratios on yield parameters of the cowpea fodder crop under two irrigation levels (75 and 100% on base of ETc) evaluated under field experiment. The results showed that higher water content at field capacity (FC) and available water content (AW) was observed with the use of 50 and 100g/plant biochar followed by hydro-char combinations. Data revealed that higher values of drainable pores (DP) were recorded after 2.7 g hydrogel, and 100 g biochar; storage pores (SP) after 2.7 hydrogel and 100g biochar, and100g biochar; whereas none useful pores were recorded after2.7 hydrogel under 75 and 100% irrigation regimes. Positive correlations were recorded between FC drainable pores DP, storage pores SP, total porosity TP, and void ratio with r-values of 0.544*, 0.983**, 0.805**; 0.814**, respectively. Also, the biological yield exhibited positive correlations with water holding capacity (WHC), FC, AW, SP,TP, and void ratio with r-values of 0.797**, 0.835**, 0.864**, 0.879**, 0.628** and 0.631**, respectively. Yield variables increased in 75% than in 100% irrigation regimes. It was concluded that the ability of biochar to enhance the hydrophysical properties of sandy soils is highly dependent on the biochar characteristics and its application rates. Furthermore, biochar applications can increase water retention in sandy soils.