Response of Pecan Yield, Quality, and Return Bloom to Water Stress During Three Fruit Development Stages

Pecan production in the western US requires regular irrigation to maintain yield and profitability.  Mature ‘Western’ cultivar pecan trees in a flood-irrigated orchard in southern New Mexico were evaluated for their response to water stress during fruit development stages.  In 2008 and 2009, trees were subjected to three treatments:  1) early season water stress (ES) – two nonconsecutive irrigations skipped during pollination, fruit set, and fruit expansion stages (May to mid-July); 2) mid-season water stress (MS) – two nonconsecutive irrigations skipped during liquid endosperm and shell-hardening stages (mid-July through August); and 3) late season water stress (LS) – two nonconsecutive irrigations skipped during the kernel filling stage (September to late October).  The control (C) was fully irrigated (16 irrigations in 2008 and 18 irrigations in 2009) according to the Mesilla Valley Pecan Growers’ Irrigation Scheduling Estimator, a model based on historic climate data.  Morning stomatal conductance (between 8AM and noon) and midday stem water potential (between noon and 4 PM) were measured one day before and two days after each irrigation.  Soil moisture was measured at 0.3 m and 0.9 m depths.  Yield was measured for each tree, and nut quality parameters (adherent shucks, nuts per kg, percent kernel, and percent blank nuts) were evaluated for a representative sub-sample of nuts from each tree.  Return bloom was measured on randomly selected shoots in the spring.  Relative to C, the combined 2008 and 2009 yield was 17% lower for ES and 26% lower for MS.  There was no difference in the combined yields between C and LS.  There were no obvious effects of water stress on nut quality in 2008.  Although return bloom was not affected by MS and LS, the return bloom was lower for ES than for C in 2009.  This experiment is a starting point for the development of a regulated deficit irrigation strategy for growing pecans in the western United States.