Evaluation of Expanded Black Cotton Soil as a Hydroponics Medium

Abstract

The traditional system of producing crops using soil (geoponics) is currently facing major challenges resulting in food deficits. An alternative is the adoption of soil-less culture (hydroponics) which is regarded as key in increasing production of vegetables, herbs and ornamentals. The study aimed at preparing a hydroponic medium from black cotton soil and rice husks. This involved moulding, firing and size reduction. The aggregates were evaluated based on dry bulk density and saturated hydraulic conductivity. The optimal conditions for preparing the medium was found to be at 750°C, 30 minutes and 9:1 for firing temperature, time and ratio of black cotton soil to rice husk (on a weight basis). This process resulted in 33% reduction in bulk density from 1.43 g cm-3 to 0.954 g cm-3 while the saturated hydraulic conductivity improved from 0.333*10-5 cm s-1 to 0.00385 cm s-1, a value that lies between the ranges of Sandy Loam and Loamy Sand. The process improved black cotton soil into a light weight aggregate medium with reduced bulk density, loose and friable aggregates, easy to drain and having moderate permeability to permit water and nutrient movement. The medium is therefore better suited to grow potted plants under indoor or outdoor conditions.