Regulated deficit irrigation and rectification of irrigation scheduling in young pear trees:: an evaluation based on vegetative and productive response

A field experiment on pear trees was designed with the objective to search for an optimum irrigation scheduling by analyzing the possible effects of over and deficit irrigation. During the first 3 years (1993-1995; first experiment), three irrigation treatments were established by irrigating at amounts 30% below (T70) and 30% above (T130) a presumed optimum rate (Control). The Control was daily irrigated following a water budget approach (FAO methodology). The results indicated that trunk growth was significantly greater in T70 than in T130 or Control and fruits of Control and T130 were not significantly larger than those of T70. In addition, T70 treatment enhanced fruit counts and bloom return. Thus, fruit yield in 1995 was 4 Mg ha(-1) lower in the Control than in the T70 treatment. This indicated that the optimal irrigation rates were closer to T70 than to the Control and therefore, reductions of irrigation were needed in the Control treatment. Consequently, in the second experiment (1996-1997), irrigation in the trees of the Control treatment was reduced during mid-season to 82% of the original Control (Control-82%). In addition, trees previously irrigated in the T70 treatment were purposely deficit irrigated at a rate of 0.5 x (Contr017821/o) during Stage II to impair fruit growth (RDI-SII). Regulated Deficit Irrigation scheduling (RDI-SI) was applied in T130 trees to reverse the low bearing behavior; deficit irrigation was applied during Stage I fruit development by reducing irrigation rates at 0.5 x (Control-82%). Trees irrigated as RDI-SI were able to recover from the low fruit counts of the previous T130 treatment. Fruit counts in RDI-SII were higher than Control-82% but fruit growth was significantly reduced. By means of the irrigation adjustment, the Control-82% achieved the highest accumulated trunk growth and largest fruit size. In conclusion, the balance between the opposing effects of deficit irrigation, which increased fruit numbers and decreased fruit size, and over-irrigation that strongly reduced fruit numbers, produced the optimum yield response. This optimum was achieved by applying adjustments to the current irrigation recommendations. (C) 2002 Elsevier Science B.V. All rights reserved.