Transpiration efficiency of lucerne under unlimited soil water conditions during the first growing season

Lucerne production is regarded as requiring high water inputs, making it necessary to understand its transpiration efficiency, especially in countries with water scarcity such as South Africa. The resurgent opportunities in the local lucerne markets prompted the publication of this short communication. The objective of this study was to quantify the transpiration efficiency of lucerne for different cutting periods during its first growing season. The study was conducted in a semi-arid area at Kenilworth Experimental Farm, University of the Free State, South Africa. Thirty field lysimeters of 1 800 mm diameter and 2 000 mm depth were arranged in two parallel rows and filled respectively with Clovelly and Bainsvlei soil types for the experiment. Surface drip irrigation was applied weekly and sub-irrigation applied daily to maintain a constant water table. The mean above-ground biomass production over 30-day cutting periods was 511 g m-2. A mean transpiration efficiency of 2.81 g m-2 mm-1 and a mean transpiration efficiency coefficient of 2.85 g kPa mm-1 were derived for the growing season. Both variables declined as the growing season progressed. Future work should ascertain the physiological and environmental factors that influence the declining trend in transpiration efficiency over the season.