Effect of Biochar on Soil Water Retention at Low Suction Levels

Abstract

Addition of biochar is shown to improve soil physical, chemical and biological properties, especially in tropical soils with low activity clay. This study was conducted to study the effects of bio-char on soil water retention of a Typic Hapludult (Red Yellow Podzolic soils) in Sri Lanka. Treatments included a control, and soil amended with 1%, 3% and 5% (by weight basis) bio-char obtained from burning rubber wood at low oxygen content. Soil core samples were used to measure soil water retention using a suction table at low suction levels (up to 100 cm). Soil texture and organic carbon contents were determined using standard methods. The results showed that addition of bio-char increased the soil water retention. Addition of bio-char significantly increased volumetric water content at the field capacity from 0.16 cm3/cm3 in the control to 0.24 and 0.33 cm3/cm3 in soils amended with 3% and 5% bio char. The field capacity of the control was low due to the low clay content and organic carbon contents of 16% and 1.35% respectively. The field air capacity, which is an indication of soil aeration, decreased significantly from of 0.42 cm3/cm3 in control to 0.3 3 and 0.22 cm3/cm3 in treatments with 3% and 5% biochar, respectively. As the limiting value for soil aeration for highland crops is 0.10 cm3/cm3' it does not become a constrain for root growth. This study shows the practicability using locally made biochar instead of coir-peat in nurseries and potting mixtures as a soil amendment to increase water retention.