Results of some soil moisture tests are presented below. The soil tests conducted were field capacity (FC), permanent wilting point (PWP) and the quantity of water at saturation point. Available water capacity (AWC) was calculated from the difference between FC and PWP. FC refers to the amount of soil moisture or water content held in the soil after excess water has drained away while PWP is the minimal point of soil moisture that a plant requires not to wilt. AWC is the maximum amount of plant available water a soil can provide. PWP can be variable for different plant types but is given here as a standard measure. FC and AWC are more dependent on soil texture and structure. Different soil types have different capacities to hold water in the soil, with sandy soils, such as the ones from the Project site, generally having low soil water content and water holding capacity.
Source: SGS, 2014.
The results in the table above show that addition of biochar to the trial site soil had a significant effect on soil moisture and that an increase in biochar was commensurate with the soil’s ability to retain moisture. Addition of 10% biochar to the soil mix resulted in a 23% increase in FC and a 30% increase in AWC compared to the control. With 20% biochar, FC and AWC increased by 26% and 40% respectively, while the addition of 40% biochar produced a 52% increase in FC and a 65% increase in AWC compared to the control sample. These figures demonstrate the potential for biochar to allow for extended growing seasons in non-irrigated agriculture and reduced irrigation inputs for irrigated or semi-irrigated agriculture.