Irrigation control of cowpea plants using the measurement of leaf thickness under greenhouse conditions

In this study, the thickness of cowpea leaves was measured with high data- and time-resolution, and the dynamics of leaf thickness was subsequently used as an input parameter for automated irrigation control at the greenhouse level. Under non-stressful environmental conditions, leaf thickness showed only minor diurnal and almost no nocturnal fluctuations. In an extreme water deficit stress scenario, leaf thickness decreased dramatically by as much as 45% within a short period of time. In a more realistic situation, leaf thickness was kept fairly constant for several days, but decreased substantially when water deficit stress became too severe for the plants to cope with any longer. This characteristic collapse of leaf thickness was used as an input parameter for the automated initiation of irrigation. Upon automated irrigation, plants re-established their nominal leaf thickness quickly and kept this leaf thickness constant for several days, until signaling the need for the next irrigation by a subsequent decrease of leaf thickness. By using the measurement of leaf thickness for irrigation control, between 25 and 45% of irrigation water could be conserved compared with a typical timed irrigation schedule.