Carry-over effects of deficit irrigation applied over seven seasons in a developing Japanese plum orchard

Abstract

Deficit irrigation is a strategy that in the short term often allows increasing water use efficiency with minimal impacts on tree performance. However, the long-term and carry-over effects of this practice have not been sufficiently investigated. Here, we report a research that was conducted over eight years in a young Japanese plum orchard planted with cv. Black-Gold in Valencia, Spain. Different deficit irrigation and crop load regimes were applied in the first seven seasons. In the last experimental season, however, all trees were well irrigated in order to explore the possible carry-over effects of the water restrictions applied previously. The results obtained indicate that under the experimental conditions of the current research (low irrigation water salinity, and Mediterranean climate with some intense rainfall events during fall and spring), deficit irrigation applied for seven consecutive seasons did not lead to accumulation of salts in the soil, a concern when deficit irrigation is applied in the long-term. Nonetheless, water restrictions impaired the fruit bearing capacity quantified as the number of fruit per unit branch length before thinning application. This effect was partly explained by a decrease in the concentration of starch reserves in the root system in one of the deficit irrigated treatments. A decrease in the fruit bearing capacity itself did not impair yield as the cultivar employed in this study required intense thinning that offset the initial differences in the number of fruit per branch length. However, deficit irrigation led to smaller trees (31% in tree shaded area in the most stressed treatment against 47% in control trees). This effect was the ultimate cause of the 29% yield reduction observed in the eighth season, when the previous deficit irrigated trees were fully watered. It is then concluded that deficit irrigation strategies in developing orchards should be used with caution. Only slight restrictions can be imposed in order to avoid the long-term carry-over effects of deficit irrigation on tree performance.