Sweetpotato Cultivation with Rice Husk Charcoal as a Soil Aerating Material under Wet Lowland Field Conditions.

Abstract

Utilization of rice husk charcoal as a soil aerating material to increase tuberous root yield of sweetpotato [Ipomoea batatas (L.) Lam.] under field conditions in a wet lowland was investigated. The rice husk charcoal was applied to ridges in the field in two ways ; the material was placed in the central layer of the ridge without mixing with soil (unmixed material treatment), or the material was thoroughly mixed with the ridge soil (mixed material treatment) . Water depth between the ridges was kept at 20 mm above the furrow level throughout the growing period in order to imitate the wet soil conditions in tropical and subtropical lowlands. A conventional ridge without the material was set as a control. The fresh and dry weights of the total phytomass were greatest in the unmixed material treatment. The fresh and dry weights of above-ground parts in the unmixed material treatment were approximately 0.6 times those in the control, while the weights of subground parts in the unmixed material treatment were approximately 4 times greater than those in the control. The unmixed material treatment gave a dry weight of tuberous roots that was 6 times greater than the control. The main stem length and leaf area were smaller in the unmixed material treatment than in the mixed material treatment and the control. Water content of tuberous roots and the shoot-root ratio were lower in the unmixed material treatment than in the control. Plants in the unmixed material treatment had a greater biomass of edible parts (tuberous roots) and a smaller biomass of non-edible parts (stems, leaves and roots other than tuberous roots) than did those in the control.