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- Author or Editor: I. Klein x
The effect of evaporative cooling on budbreak and yield of Vitis vinifera L. (‘Perlette’ and ‘Thompson Seedless’) vines grown in the southern Jordan Valley in Israel was investigated. Overhead microsprinklers were operated from 0600 to 1800 hr daily during the autumn and winter months, either alone or in combination with cyanamide sprays after pruning. Evaporative cooling decreased the temperature of buds exposed to direct sunlight from 30° to 16°C and that of shaded buds from 25° to 13°. Evaporative cooling induced an early uniform budbreak. However, when evaporative cooling was combined with cyanamide spray, its effect was evident only during the initial phase of bud emergence. In 1985 cyanamide spray and evaporative cooling alone increased yield of ‘Perlette’ by 6% and 6% to 24%, respectively, and by 17% to 46% when both treatments were combined. In 1986 prolonged evaporative cooling increased the yield of ‘Perlette’ by 25% but, in combination with cyanamide, by only 11.6% over the unwetted cyanamide-treated control. In both years, evaporative cooling with or without cyanamide advanced fruit maturation.
Mature almond trees [Prunuis dulcis (Mill) D.A. Webb] growing on a very light-textured soil (Delhi sand) were “pulsed” in 1980 with a soil application of 15N-depleted ammonium sulfate. Leaching of labeled N from the soil and dilution (with unlabeled N carriers) of residual label in the soil minimized uptake of labeled N from this soil in subsequent years. The percent annual depletion (PAD) of labeled N in tissue samples was 50% and represented the percent annual influx of tree N from the soil N pool. Nitrogen assimilated in previous years also represented 50% of total tree N. The fractional contribution of N absorbed in any prior year, relative to the total pool of storage N, may be expressed as 1/(2)x, where x represents the number of years prior to the current year. The PAD, as measured in tissue samples, was greater in trees growing in the Delhi sand than among comparable trees growing in a heavier-textured soil (Yolo silty clay loam). A hyperbolic depletion function was fitted to the data to predict endpoints of tissue labeling. These endpoints were estimated to be 8.5 and 86.1 years on the light- and heavy-textured soils, respectively.
The interaction between irrigation and crop load with respect to fruit size distribution was investigated in a `Golden Delicious' apple (Malus domestica Borkh) orchard located in a semi-arid zone. Irrigation levels during the main fruit expansion phase ranged from 0.42 to 1.06 of the Class A pan evaporation coefficient. Crop load was adjusted to 100 to 450 fruit/tree in the 1250 trees/ha orchard by hand thinning. Total yield was not affected by irrigation level up to a crop load of 200 fruit/tree. Yield of all grades >65 mm was affected by irrigation level for higher crop densities. The yield of fruit of diameter <75 mm was not affected by increasing the Class A pan evaporation coefficient above 0.75. Our data indicate that availability of assimilates may limit the size of fruit with potential to grow larger than 70 mm in diameter at all crop loads higher than 200 fruit/tree. This limitation increases with decreasing irrigation level. The volumetric relative growth rate (VRGR) increased with irrigation level and with decreasing crop load. VRGR was more affected by crop load than by irrigation level in the ranges studied.
Exposure to photosynthetically active radiation and the consequent effect on leaf mass per unit leaf area (SLW) and nitrogen (percent dry weight and μg·mm-2) allocation within tree canopies was investigated in walnut (Juglans regia `Serr' and `Hartley') trees. Percent contribution of discrete light flux densities below light saturation (100-700 μmol·s-1·m-2) to the total light exposure of individual spurs, exposed up to 9 hour·day-1 to saturating light (>700 μmol·s-1·m-2), was minimal (<1 hour), indicating that individual spurs were either exposed or shaded most of the day. SLW and N content per unit leaf area of individual spurs were highly correlated (second-order polynomial curve fit) with light exposure within the tree canopy, indicating uneven allocation of available N for optimal utilization. Nitrogen expressed as percent dry weight was not correlated with light exposure and SLW. Leaf N content per leaf area was highly correlated (linear fit) with SLW.
Localized and carry-over effects of light exposure [as inferred from specific leaf weight (SLW)] on spur viability, flowering, and fruit set were monitored in selected spurs throughout walnut (Juglans regia, cvs. Serr and Hartley) tree canopies. Shaded spurs (i.e., average SLW <4 mg·cm-2) were predisposed to die during the winter, and spur mortality was accentuated among spurs that had borne fruit that season. More catkins and distillate flowers per spur were characteristic of the more exposed positions within the canopy (as indicated by SLW) during the previous summer and following an “off” year. In exposed `Serr' canopy positions (SLW >5 mg·cm-2), catkin and Pistillate flower maturation was reduced in fruiting spurs by 60% and 30%, respectively, in the subsequent year relative to vegetative spurs. In `Hartley', the number of distillate flowers was also reduced by 35% on spurs that fruited the previous year relative to spurs that had been vegetative. Maximum rates of return bloom and fruit set were evident in spurs exhibiting the highest SLW and N per unit leaf area (NA), specific to each cultivar. Among spurs of both cultivars, distillate flower development was more sensitive to shading in the previous season than was catkin development. Shell weight of `Serr' varied positively with SLW, but kernel weight, fruit N, and oil concentration did not vary “with SLW in either cultivar.
Mature almond [Prunus dulcis (Mill) D.A. Webb] trees growing on light-(Delhi sand) and heavy-textured (Yolo silty clay loam) soils were fertilized with 15N-depleted ammonium sulfate at different times during the year to permit direct measurement of fertilizer N within the trees. The distribution of fertilizer N between vegetative and reproductive organs was monitored during both the year of application, 1980, and the subsequent year. The later that fertilizer N was applied during the season, the less fertilizer N was recovered in the fruit and leaves that year, and the greater its N contribution to these organs was the following year. Isotopic labeling of fruit and leaves appeared to be relatively unaffected by soil texture during the year of fertilizer application. During the subsequent year, however, the recovery of fertilizer N by fruit and leaves was 2-fold greater on the heavy-textured soil than on the light-textured soil. Recovery of labeled N in fruit was relatively low on both soil types following application of fertilizer during the dormant period. Isotopic N was recovered in fruit in both 1980 and 1981 and constituted about 20% to 28% of fruit N at most. About 25% of the applied N was removed in the fruit on the heavy-textured soil over a 2-year period. Up to 1 kg N per tree was removed annually in the harvested fruit.
The interactions between irrigation and crop level with respect to fruit size distribution and midday stem water potential were investigated for 3 years in a nectarine (Prunus persica L. `Fairlane') orchard located in a semi-arid zone. Wide ranges of crop loads and irrigation rates in stage III were employed, extending from practically nonlimiting to severely limiting levels. Irrigation during stage III of fruit growth ranged from 0.63 to 1.29 of potential evapotranspiration (ETp). Fruit were hand thinned to a wide range of fruit levels (300 to 2000) fruit/tree in the 555-tree/ha orchard. The yields and stem water potentials from 1996, 1997 and 1998 were combined together and the interrelations among yield, crop load and stem water potential were examined. Fruit <55 mm in diameter growing at 400 fruit per tree were the only ones not affected by irrigation level. The yield of fruit of 60 to 75 mm in diameter increased with irrigation level, but only a slight increase was observed when the irrigation rate rose above 1.01 ETp. A significant decrease in the yields of 60 to 65, 65 to 70, and 70 to 75-mm size grades occurred at crop levels greater than 1000, 800, and 400 fruit per tree, respectively. Midday stem water potential decreased with increasing crop level, and it is suggested that midday stem water potential responds to crop load rather than crop level. Relative yields of the various size grades were highly correlated with midday stem water potential. It was suggested that the midday stem water potential integrates the combined effects of water stress and crop load on nectarine fruit size.
The interactions between irrigation and crop level with respect to fruit size distribution and soil and stem water potentials were investigated in a nectarine (Prunus persica (L.) Batsch. `Fairlane') orchard located in a semiarid zone. Irrigation treatments during stage III of fruit growth ranged from 0.62 to 1.29 of potential evapotranspiration (ETp). Fruit were hand thinned to a wide range of fruit levels (200 to 1200 fruit/tree in the 555-tree/ha orchard). Total yield did not increase with increasing irrigation rate above 0.92 ETp in 1996 and maximum yield was found at 1.06 ETp in 1997. Fruit size distribution was shifted towards larger fruit with increasing irrigation level and with decreasing crop level. The two highest irrigation treatments had similar midday stem water potentials. Our findings indicate that highest yields and highest water use efficiency (yield/water consumption) are not always related to minimum water stress. Total yield and large fruit yield were highly and better correlated with midday stem water potential than with soil water potential. This confirms other reports that midday stem water potential is an accurate indicator of tree water stress and may have utility in irrigation scheduling.