Water use by ‘Columbia Star’ trailing blackberry in western Oregon

Abstract

Two, large weighing lysimeters were installed near the center of a level field and used to measure crop evapotranspiration (ET_c) of trailing blackberry (Rubus L. subgenus Rubus Watson ‘Columbia Star’) in western Oregon, USA. The lysimeters were constructed from steel and included an inner soil tank (1.0-m wide × 1.5-m long × 1.7-m deep) positioned within a slightly larger outer tank on four hermetically sealed, shear-beam load cells. Plants were spaced 1.5 × 3.0 m apart (one plant/lysimeter; 2153 plants/ha), irrigated by drip, and trained to a vertical two-wire trellis system. During the first year after planting, when only non-fruiting primocanes were present, ET_c totaled 120 mm, or 18% of total potential evapotranspiration (ET_o) for the growing season. That year, crop coefficients (K_c), calculated by dividing ET_c by ET_o obtained from a nearby agricultural weather station, was 0.24 when the measurements were initiated in early July 2020 and, with exception of a brief decline due to heavy wildfire smoke, steadily increased to 0.81 before leaf fall in early October. The following year, ET_c doubled, reaching a total of 275 mm, or 34% of total ET_o. At that point, K_c increased from 0.30 at budbreak to 0.48, before dropping to 0.27 when the plants were scorched during a heat dome event in late June. Yield was lower than expected in year 2 (2.15 kg/plant) due to 39% fruit loss from heat damage. Afterwards, K_c slowly increased with primocane development to its highest value of 0.85 just before leaf fall. By the third year, the plants reached full production (8.46 kg/plant), and ET_c nearly doubled again, reaching a total of 511 mm, or 71% of total ET_o. Weekly K_c in year 3 increased from an average of 0.55 in late June to 0.88 in mid-August and stayed relatively constant until the plants were pruned and trained in late September, where it dropped to 0.32. At full production, the plants required an average of 280 L of water to produce each kilogram of fruit. Soil water content readings indicated the plants extracted water primarily from the top 0.6 m of the soil profile on cooler days and up to 1.2 m deep on warmer days. Each year, ET_c and K_c increased primarily with new primocane growth but fluctuated due to unusual weather events (i.e., wildfire smoke, heat dome) and pruning and training during the growing season. Results from the study provide new K_c values for estimating crop water requirements and scheduling irrigation from establishment to full production in trailing blackberry.