Global diminishing water resources, especially due to climate change have serious impacts on evaporation (E) from the soil surface, transpiration (T) from plants (crops) and grain yield, which relates to water use efficiency of different crops. A study was conducted at Kenilworth over two wheat cropping seasons (2007 and 2008) with the objectives of: (i) evaluating the effect of soils and seasons on T, E and yield, and (ii) relating these parameters to transpiration efficiency coefficient. The treatments included two soil types and two soil surface treatments (bare and mulched), which were all replicated four times. Weekly irrigation was done using a surface drip system while maintaining the water table at a constant depth. Soil water content was monitored using a neutron probe. Neither soils nor seasons were found to significantly influence the partitioning of evapotranspiration (ET), and T varied from 74 to 76% of ET while E varied between 24 and 26%. Surface treatments caused significant differences in grain yield in both seasons. Reducing evaporative loss improves the water productivity of wheat, which has an important implication in dryland farming.

Much has been reported on the agronomic aspects of canola (Brassica napus L.), but there is a lack of information on the crop's transpiration (T). The objective of this study was to evaluate the influence of soils and growth periods on the T, transpiration efficiency (TE) and transpiration efficiency coefficient (TEC) of canola under irrigation. Twenty-four lysimeters (2.5 m 2) were used for the study. The experimental treatments comprised two soil forms and four growth phases during the reproductive stage, all replicated three times. Irrigation was applied weekly through a surface drip system and a water table was maintained at 1200 mm from the surface through subirrigation. Soil water content was monitored using a neutron probe. The contribution of an accessible water table was up to 60% of the total T requirement of the crop during the investigation period. TE, calculated as above-ground biomass per unit transpiration, ranged between 2.81 and 3.32 g m −2 mm −1. TEC, obtained by normalizing TE to the vapour pressure deficit, resulted in values between 3.82 and 4.99 g kPa mm −1. Both TE and TEC were significantly different between growth periods and not amongst soils.