Responses to Saturation Deficit in a Stand of Groundnut (Arachis hypogaea L.). 2. Growth and Development

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Abstract
Stands of groundnut were grown in four glasshouses with the maximum saturation deficit (D) of the air limited to 1.0, 2.0, 2.5 or 3.0 kPa. The soil was near field capacity when plants emerged and no water was applied thereafter. In a fifth glasshouse, a stand was grown at low D on soil irrigated to field capacity every few days. Developmental processes such as timing of flowering, pegging and pod formation were unaffected by D, but the numbers of branches, flowers and pegs were reduced in the drier treatments. Measurements during the first 30 d showed that in the drier treatments leaf growth was reduced, and the partitioning of dry matter into roots was enhanced. In the unirrigated stands, dry matter production in shoots was reduced by 40 per cent as the maximum D increased from 1.0 to 3.0 kPa. Growth was affected through reductions both in leaf area (and therefore light interception) and in the productivity per unit of light intercepted. These responses to D and soil water were linked to changes in bulk water potential of leaves. Productivity per unit of water transpired (q) decreased with increasing D. The product of q and the mean daytime value of the difference in vapour pressure between leaf and air was more conservative than q, and ranged from 3.1 to 5.6 g kPa kg−1.