Experimental control of water status in an apple orchard

Abstract

A system of under-tree polyethylene tent covers was used in conjunction with irrigation treatments to induce a range of soil moisture regimes in a Bramley apple orchard. The treatments included one of covers plus added irrigation to determine any effects of the covers independent of the effects on soil water status. The covers successfully reduced precipitation reaching the root zone, so that quite large differences in soil water content between treatments were observed. There was, however, strong evidence that stomatal closure in the drier treatments minimized treatment differences in leaf water potential. This effect was more marked in younger trees. In the first year this stomatal closure was so effective that ‘over-control’ occurred such that the droughted trees had higher leaf water potentials than the irrigated trees at the end of the season. Generally, however, leaf water potentials were between 0.1 and 0.2 MPa (1 and 2 bar) lower in the droughted than in the irrigated trees. Comparisons of soil temperatures under drought covers and either a cover plus irrigation treatment or natural rainfall indicated that observed differences were related to altered soil moisture regime rather than any direct effect of covers on air flow or radiation climate.