EFFECTS OF SOIL MOISTURE STRESS ON THE WATER RELATIONS AND WATER USE OF GROUNDNUT STANDS

Abstract

SummaryThe work described here formed part of a detailed study of the effects of temperature and water stress on growth and development in groundnut (Arachis hypogaea L.). Stands of plants were grown in controlled environment glasshouses at mean air temperatures of 25, 28 and 31 °C. Half of each stand was irrigated whenever soil water potential at 10 cm reached –20 kPa. The other half received no further irrigation after sowing, when the soil profile was at field capacity. The effects on plant water status, stomatal conductance and water use were investigated regularly during the growing season.Leaf water potential (Ψ1), turgor potential (Ψp) and stomatal conductance (g1) were already reduced in unirrigated plants by 29 d after sowing (DAS), when leaf area index (LAI) was still below 0.5; g1 was more strongly affected than water status. These differences persisted throughout the season as stress increased, g1 was poorly correlated with Ψ1 and Ψp and of ten exceeded 2 cm s−1 in wilted leaves. LAI was not affected before 40 to 45 DAS but was reduced by 20 to 25 % in unirrigated plants between 60 DAS and final harvest. The decreases in g1 and LAI reduced canopy conductance by up to 40 %. The conservative influence of decreased g1 in unirrigated plants was negated by increases in leaf‐to‐air vapour pressure difference caused by their higher leaf temperatures. Transpiration rates were therefore similar in both treatments and the lower total water use of the unirrigated stand resulted entirely from its smaller LAI. Unirrigated plants made less vegetative growth but produced more pegs and pods. However, impaired pod‐filling reduced pod yields by around 35 %.