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- Author or Editor: P. D. Mitchell x
From the mean of weekly measurements of diameter, volume, and weight of the pear (Pyrus communis L. ‘Bartlett’ and ‘Packham Triumph’), equations were developed for predicting fruit volume and weight from diameter. Equations also are presented for the relationship between days from full bloom and diameter and length (linearly related) and volume, fresh weight, and dry weight (curvilinearly related).
Root spread from close-planted (5.5 × 1 m) peach trees [Prunus persica (L.) Batsch] was restricted when irrigated from trickle or microjet outlets. Roots spread less under trickle, and trees grew more slowly but cropped earlier. Fruit set heavily on both treatments in 5th leaf. The results suggest that irrigation technique can be used as a management tool affecting tree growth and productivity for close-planted orchards.
A range of irrigation levels was compared in specific periods of fruit development to determine their suitability for control of tree vigor and yields in ultra-dense orchards of peach [Prunus persica L. Batsch] trees. Where trees in the 3rd leaf were trickle-irrigated with 4 levels (100, 50, 25, and 12.5%) of replacement of Eps (evaporation over the planting square) during the period of rapid vegetative growth, both frame and fruit growth declined as irrigation quantity decreased. In the following period of maximum fruit growth, 130% of Eps replacement increased vegetative growth but not fruit growth compared to 100% Eps. The fruit, however, grew faster in this period on those trees which had received low levels of Eps replacement in the earlier period of maximum vegetative growth. The net result was similar final fruit size and yield between treatments, combined with control of vegetative growth at the lower levels of Eps. A large saving in irrigation water was obtained at the lower levels of replacement of Eps.
Three levels of water deficit generated by 3 levels of irrigation applied at times of rapid vegetative growth and/or slow fruit growth were compared to determine their suitability for restricting vegetative growth on 5-year-old ‘Bartlett’ pear (Prunus communis L.) trees trained to a Tatura Trellis. For the period of Regulated Deficit Irrigation (RDI), the amount of water applied replaced 92%, 47%, and 23% of the evaporation calculated over the planting square (Eps). In the subsequent period of rapid fruit growth until harvest, all trees were irrigated with 150% Eps to ensure that the wetting pattern from the trickle system wetted the entire root zone. Shoot and frame growth declined in proportion to the water deficit. Fruit tended to grow more slowly on the 23% than 46% treatment during RDI, but growth on the 46% and 92% Eps treatments was similar. In the subsequent period of full irrigation, fruit growth initially was significantly faster on the RDI treatments, and the same trend was maintained for most of the remainder of fruit growth. The net result was that yield was marginally increased RDI treatments. In the subsequent season, flowering was increased on trees recieving RDI in the previous season.
Root competition (tree density), summer pruning, and regulated irrigation were studied to determine whether they can be used to control tree vigor and productivity in ultra-dense orchards of peach [Prunus persica (L.) Batsch]. All methods appeared to inhibit tree growth, but regulated irrigation combined with root competition generated from high tree density was most effective. Fruit yields and fruit growth were significantly increased (up to 30%) by high tree density combined with low rate of water application when water stress limited shoot growth but stimulated subsequent fruit growth. Periods of low rate of water application are specified.
Withholding irrigation (WI), followed by regulated deficit irrigation (RDI) at 2 levels, were compared with conventionally scheduled irrigation during rapid vegetative growth on ‘Bartlett’ pear (Pyrus communis L.) trees. All trees were irrigated at an increased common level during subsequent rapid fruit growth, by which time most vegetative growth had ceased. Irrigation effects were studied at 3 tree spacings (4 × 1 m, 4 × 0.75 m, and 4 × 0.5 m). Shoot and frame growth was related directly to early irrigation treatment before summer pruning. However, significant shoot growth that was reinitiated following summer pruning during one year increased on RDI treatments. The improved tree water status gained by changing from RDI to full irrigation in both years and from WI to RDI in the first year stimulated the growth rate of the total crop on the RDI treatments. Gross yield was increased significantly by WI and RDI in both years. Blossom density also was increased. Preliminary WI increased the control of vegetative growth by RDI when the soil was wet at flowering.
After initially withholding irrigation (WI) to dry out the root zone of pear trees, regulated deficit irrigation (RDI) applied to replace 23% and 46% of evaporation over the planting square (Eps) was compared with 69% and 92% Eps applied during the WI and RDI periods, respectively (full irrigation). Irrigation was increased to 120% Eps on all treatments after rapid fruit growth commenced. Leaf water potential (ψ1) measured at dawn and midday became less negative during RDI than during WI but in both periods was more negative than the control (69%/92% Eps). On the other hand, ψ1 of treatments receiving WI and RDI became less negative than the control when all irrigation treatments were increased to 120% Eps. Withholding irrigation followed by RDI reduced vegetative growth by 52%. In contrast, however, WI did not inhibit fruit growth, while, during RDI following WI fruit, growth was stimulated. A similar but greater stimulation of fruit growth (consistent with relatively less negative ψ1) was measured on WI/RDI plants when all treatments received 120% Eps. This stimulation of fruit growth increased yields by about 20%. The results indicate fruit osmoregulate to maintain and/or increase growth at the expense of inhibited vegetative growth when WI and or RDI reduce ψ1 in spring to values approaching −0.5 MPa at dawn.
Individual and interactive effects of restricted root volume (RRV) and regulated deficit irrigation (RDI) on vegetative growth and mineral nutrition of peach trees [Prunus persica (L.) Batsch (Peach Group) `Golden Queen'] were studied over 3 years (1992-95). Trees were grown in lysimeters of five different volumes (0.025, 0.06, 0.15, 0.4, and 1.0 m3) with either full or deficit (RDI) irrigation. Increasing soil volume increased vegetative growth as measured by trunk cross-sectional area (TCA) (linear and quadratic, P < 0.011) and tree weight (linear, P < 0.001) with the final TCA ranging from 29.0 to 51.0 cm2 and tree weight ranging from 7.2 to 12.1 kg for the smallest to largest volumes. Root density measured at the completion of the experiment decreased with increasing soil volume (linear and quadratic, P < 0.001) with root length density declining from 24.0 to 2.0 cm·cm-3. RDI reduced vegetative growth by up to 70% as measured by weight of summer prunings. Root restriction was effective in controlling vegetative vigor and is a viable alternative for control of vegetative growth. Mineral nutrition did not limit tree growth.
Individual and interactive effects of restricted root volume (RRV) and regulated deficit irrigation (RDI) on productivity and water use of peach trees [Prunus persica (L.) Batsch `Golden Queen'] were studied over 3 years (1992-95). Trees were grown in lysimeters of five different soil volumes (0.025, 0.06, 0.15, 0.4, and 1.0 m3) with either full or deficit (RDI) irrigation. In Years 3 and 4, fruit size was reduced by up to 30% on trees in the two smallest volumes. Tree water use was positively related to increasing soil volume (linear, P < 0.001; quadratic, P < 0.011) in all years ranging from 1.8 to 4.4 L·mm-1 Epan in the post-RDI period of Year 2. Water use of deficit-irrigated trees was less than fully irrigated trees and there was an interaction between soil volume and irrigation treatment during RDI. Water relations did not limit growth or productivity. Tree water use was reduced under root restriction as a consequence of canopy demand rather than leaf function. Results suggest that a combination of restricted root volume and development of water stress achieve the RDI response in the Goulburn Valley, Australia.
Sustainable alternatives for saline drainage water management in areas such as California's San Joaquin Valley are needed. Previous work has demonstrated the short-term potential for reuse of saline drainage water for irrigation in this area. Results from our 6-year cyclic drainage reuse study, however, indicate that soil structural problems may occur which can greatly reduce stand establishment and crop yields in periodically salinized soils. To prevent these problems, we are evaluating the effectiveness of winter cover crop incorporation and gypsum applications relative to conventional fallows, for improving/maintaining soil physical properties and crop productivity in cyclically salinized soils. Six winter cover crop/fallow treatments have been imposed upon a rotation of tomatoes, tomatoes and cotton as summer crops. By monitoring water use, relevant soil physical and chemical properties as well as crop performance during the course of this 3-year rotation study, we are assessing the potential benefits and constraints of using winter cover crops in drainage water reuse systems.