Effect of Biochar Derived from Different Crop Residues on Soil Water Retention

Abstract

The water retention capacity of Sierra Leone soils is low due to low organic matter content and the dominance of highly weathered low activity clay minerals such as kaolinite and iron and aluminum sequioxides. It is therefore essential to seek efforts to improve water retention capacity of soils in order to improve crop growth and yield. This research was carried out to study the water retention properties of biochar derived from different crop residues and their influence on soil water retention. The study was conducted at the Njala University Quality Control Laboratory, Njala Campus in Southern Siera Leone (Latitude 8oN and Longitude 12oW). Six biochar types from six crop residues (rice straw, rice husk, groundnut, maize stover, pigeon pea and cowpea) were studied. For each biochar, 10g was saturated with water by capillary action and suspended to allow drainage of excess water. The amount of water retained by biochar was determined by drying in oven to constant weight. The water retention capacity of each soil-biochar mixture was determined in a similar manner; where, 10g of a fine sandy loam soil was mixed with biochar at different rates (0.2, 0.4, 0.6, and 0.8g/10g soil). The study revealed that the water retention capacities of the different biochar types depended on the biomass type. However, the retention capacity of different biochar types was not clearly reflected on their soil-biochar mixtures. For example, biochar derived from Maize stover which had lower water retention capacity than Rice straw biochar showed higher soil water retention than Rice Straw biochar in the biochar-soil mixture. This showed that water retention capacity of pure biochar is not a direct measure of its capacity to improve soil water retention. However, this requires further investigations. The study also revealed that water retention capacity of biochar-soil mixtures increased with increasing biochar application levels. However, signgificant effects were observed with higher application rates. Fractionation of biochar did not produce any regular pattern in water retention.