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- Author or Editor: David J. Chalmers x
- HortScience x
Nashi pear (Pyrus serotina Rehder, cv. Hosui) trees were planted in 12 computerized 1m-wide drainage lysimeters in September 1987. During the 1990 season tree water use was monitored via lysimeter and neutron probe readings. Diurnal leaf water relations were studied using a pressure chamber for water potential (ψ) and a porometer for leaf conductance (gs). Xylem sap trunk flow velocities were measured with an experimental heat pulse device and converted to xylem flux. Close agreement existed between 24 hr xylem flux and lysimeter water use when comparing trees with different soil water content. Xylem flux also was very sensitive to changes in evaporative demand. During 9–13 day drying cycles pre-dawn ψ became progressively lower, morning decline more rapid, and afternoon recovery slower. The diurnal gs pattern also shifted during drying cycles, such that gs of water stressed trees always decreased from time of first measurement of sunlit leaves rather than increasing during the morning as on non-stressed trees. Late afternoon was the best time to distinguish between fully irrigated and stressed trees using gs measurements.
Abstract
The Tatura Trellis was developed from principles to overcome problems identified in existing cultural systems (2, 3, 6). For optimum early bearing and yield, we wanted a) a tree design that fills the allotted space quickly, resulting in optimum land use; b) a uniform and controlled distribution of leaves and fruit to improve light interception (16) and photosynthetic efficiency (5); c) an ordered branch and leaf array that diminishes light competition within and between trees, so as to minimize the effects of crowding that usually result from high plant densities, especially with peach trees; d) close planting to create root competition, thereby reducing vegetative vigor while increasing fruitfulness (4); and e) large tree numbers per hectare for high yields early in the life of the planting. In addition, we proposed that within the above constraints, the new system should be simple to mechanize. The requirements we considered important were f) an orchard with planar, though not necessarily horizontal or vertical, surfaces for easy positioning of machines and aids; g) a canopy under which machines can operate to recover fruit simply during harvesting, and over the canopy for summer pruning; h) a shallow canopy to decrease the chance of fruit striking limbs or other obstructions, which could damage the fruit after they were removed mechanically (30); i) a shallow canopy to increase penetration and coverage of protective sprays; and j) single limbs that repeat at regular intervals to simplify the positioning of mechanical devices.
The design of a type of drainage lysimeter, as tested with trees of Pyrus serotina Rehder var. culta Rehder `Hosui' is described. All lysimeter operations and monitoring of irrigation and drainage volumes were managed by a “multi-tasking” controller/datalogger. It was possible to apply different irrigation levels to each of three sets of four random lysimeters. Evapotranspiration (ET) was calculated using a conservation of water equation, with differences between irrigation inputs and drainage outputs corrected for changes in soil-water content. ET ranged between 3.3 and 10.7 liters/tree per day in well-watered, noncropped trees in late Summer and Fall 1990. These rates correspond to ET of 0.13 to 0.43 liter·cm-2·day-1 and 0.96 to 3.10 liters·m-2·day-1 on trunk cross-sectional area and canopy area bases, respectively. The correlation coefficient between ET and Class A pan evaporation was >0.9 during this period. Weekly crop coefficients for the well-watered trees averaged 0.52 when calculated on a canopy-area basis. When irrigation was withheld for 18 days, the crop coefficient declined to 0.38. There were no differences in ET between trees growing in the two soil profiles, despite significant differences in soil water distribution.