The Potential of Biochar to Enhance the Water Retention Properties of Sandy Agricultural Soils

The impact of climate change has become increasingly severe in drylands, resulting in heat stress and water deficiency and, consequently, reducing agricultural production. Biochar plays an important role in improving soil fertility. The properties of sandy soils where water deficiency occurs with a greater frequency need to be enhanced by biochar amendments to increase the water retention capacity (WRC). Few studies have reported the effects of biochar on the readily available water (RAW) of these soils or an evaluation of the optimal application rate of the biochar. In this study, we aimed to assess the effect of different biochar types and application rates on the soil properties related to water retention. Under laboratory conditions, we amended sandy soil with four different types of biochar (woodchip (WBC), waterweed of Ludwigia grandiflora (WWBC), poultry litter (PLBC) and bagasse (BBC)) at rates of 0%, 5%, 10%, 15%, 25%, 50%, 75% and 100%. Soils treated with zeolite and perlite, both conventional materials, were arranged for a comparative study. The water content in the amended soils was recorded at saturation, field capacity, wilting point and oven-dry. Our results show a reduction in the bulk density by increasing the amendment rate across all biochar types. Although the WRC increased with the application rate, the RAW reduced and peaked at a 5% (v/v) biochar content for almost all the biochar types. WBC and WWBC showed the highest RAW increments of 165% and 191%, respectively, at a 10% (v/v) rate. In most cases, higher rates (such as 75% (v/v) of PLBC) caused negative effects on the RAW. Following these results, it is clear that both the biochar type and the application rate significantly influence the hydrological properties and the RAW capacity of sandy soils. A 5% (v/v) biochar amendment could significantly improve the readily available water to mitigate drought in sandy agricultural soils