Measurement of water-use by &lt;i&gt;Jatropha curcas&lt;/i&gt; L. using the heat-pulse velocity technique

M.B Gush

doi:10.4314/wsa.v34i5.180655

Abstract

In response to the proposed introduction of the potential bio-diesel species Jatropha curcas (Linnaeus) to South Africa, field experiments were conducted to investigate its likely water-use impacts relative to other forms of vegetative land use. As no existing water-use data could be found for this species worldwide, sap flow in Jatropha curcas trees was measured continuously for a 17-month period at two sites in eastern South Africa. These consisted of young (4-year-old) trees at a relatively wet site and mature (12-year-old) trees at a dry site. The heat-ratio method of the heat-pulse technique was utilised, together with measurements of meteorological variables and soil water. Sap- flow rates varied according to tree age, season, prevailing meteorological conditions, and soil moisture levels. Peak sap-flow rates occurred during the warm wet summer months, but due to the deciduous nature of the species, water use was negligible during winter. Scaled-up sap-flow measurements resulted in estimates of total annual transpiration of 1 983 l (147 mm) for a 4-year-old J. curcas tree, and 4 884 l (362 mm) for a 12-year-old J. curcas tree. The study concluded that the J. curcas trees studied were conservative in their water use, and were unlikely to transpire more water than indigenous vegetation types of the area.

Highlights

In response to rising oil prices and the quest for alternative, economically viable and environmentally sustainable forms of energy, certain plant species with bio-energy potential have been proposed for large-scale planting and bio-fuel production
In South Africa, the government has received numerous requests for permission to plant this species, but, apart from certain trial plantings, has imposed a moratorium on commercial plantings. This has been due to, amongst other considerations, the extremely limited data available on its potential environmental impacts. This knowledge gap is of particular concern in a dry country such as South Africa, where evapotranspiration from vegetation is the component of the water balance that accounts for the greatest loss of water from catchments
Variations in mean maximum and minimum temperature, total rainfall and total solar radiation measured at OSCA and Makhathini are illustrated in Figs. 2 and 3 respectively

Summary

Introduction

In response to rising oil prices and the quest for alternative, economically viable and environmentally sustainable forms of energy, certain plant species with bio-energy potential have been proposed for large-scale planting and bio-fuel production. International interest in Jatropha curcas as a drought- tolerant, fastgrowing, renewable bio-energy crop has grown significantly in recent years Countries such as India have initiated large-scale plantings of J. curcas in efforts towards the increased use of bio-diesel as an alternative to fossil fuel imports (Francis et al, 2005). In South Africa, the government has received numerous requests for permission to plant this species, but, apart from certain trial plantings, has imposed a moratorium on commercial plantings. This has been due to, amongst other considerations, the extremely limited data available on its potential environmental impacts ( water-use). Plant sap flow (transpiration) was measured using the heat-pulse technique, together with measurements of meteorological variables and soil moisture at two sites in KwaZulu-Natal Province, South Africa (Gush and Moodley, 2007)

Methods

Results

Conclusion