Soil and nutrient loss under rozelle (Hibiscus subdariffa L. var. altissima) at Khon Kaen, Thailand

Abstract

Rozelle (Hibiscus subdariffa L. var. altissima) was grown in hydrologically defined plots at Khon Kaen, Thailand (latitude 16°30′N, longitude 102°50′E, altitude 195 m). The loss of water, soil and plant nutrients from these plots under different types of soil management was measured for the three growing seasons from 1989 to 1991. Plots were 30 m long, 5 m wide, and slope 3.6%, and the soil was a loamy sand with 5% clay and 79% sand. Treatments included up and downslope cultivation, contour cultivation with and without subsoiling, and no tillage. A bare plot was also installed to measure soil erodibility parameters. Runoff and soil loss from treatment plots was greatest from the up and downslope cultivation treatment, though not exceeding 20% of rainfall or 4 tonnes/ha respectively in any growing season. Despite the modest loss of soil by water erosion, the average enrichment ratio for nitrogen was 5.5. Thus the loss of nitrogen would be important on this sandy soil, especially as rozelle is commonly grown in this region with little or no fertilizer input. Soil, water and nutrient loss was also measured for a bare soil plot. Soil loss from this plot was about ten times higher than for the most erosive treatment. Most eroded sediment was transported from the bare plot in broad, shallow rills in which the sediment concentration was close to the transport limit, which was less than the concentration produced by rainfall detachment and re-detachment because of the low slope of the plots, and the high detachability of this soil. Of the four management treatments investigated, contour cultivation emerged as the most practicable. Subsoiling was ineffective in further reducing runoff and soil loss, and if no cultivation was carried out, plant yield was reduced, even though this treatment was most effective in reducing soil erosion.