Influence of irrigation rate on the rehydration of olive tree plantlets

The scarcity of water for use in agriculture - a consequence of its use in other areas - has made deficit irrigation common on irrigated farmland. Regulated deficit irrigation involves scheduling periodic cycles of water stress over the growing season that result in no (or only a very slight) reduction in yield. The complete recovery of plant water status is, however, necessary if losses are to be minimised. In this work, cv. Picual olive plants, grown in pots in Ciudad Real (Spain), were withheld irrigation for 26 days, and then subjected to one of three different irrigation rates during the recovery period. Two treatments were designed to provide rapid recovery but had different soil moisture targets: T1 involved irrigation to field capacity, and T2 replaced half of the water consumed during the drought period. The third treatment, T3, allowed rehydration to field capacity but at a lower irrigation rate than in either T1 or T2; the pots only reached this soil moisture level after 2 weeks. Compared to a fully irrigated control, the delay in recovery between leaf conductance and mid-day stem water potential was shorter in T1 and T2 (just 1 day) than in T3 (11 days). The T2 plants showed a trend towards lower stem water potentials compared to the controls, while the T3 plants showed a trend towards lower leaf conductance. In all treatments the recovery of water potential was very fast--less than 5 days. The differences in the recovery of leaf conductance and mid-day stem water potential are probably related to root flow. Varying irrigation rates could provide a new means of controlling - and even reducing - the intensity and length of water stress during the recovery period. Measuring the water potential alone during this period may not provide an accurate picture of plant water relations.