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- Author or Editor: A. Richard Renquist x
A decision support system has been developed to help Colorado fruit growers with apple (Malus domestica Borkh.) thinning. This system can also be used as a teaching aid and as a tool for generating research hypotheses. The system determines if fruit thinning is needed by identifying catastrophic events that would eliminate the need for thinning. The major function of this decision support system is determination of tree responsiveness to chemical thinning agents. This is accomplished through analysis of the user's answers to questions related to the physiological status of the trees, environmental data, bearing history, and the apple variety in question. On the basis of the above analysis, two sets of recommendations are presented: general recommendations based on the variety selected, and specific ones for that variety based on growth stage and tree responsiveness to thinners. The user also is provided with the rationale for the recommendations.
Abstract
A disorder of red raspberry (Rubus idaeus L.) in an area exposed to high temperature and solar radiation has been identified as a form of solar injury. Specific fruit maturity stages were defined and susceptibility to injury was found to rapidly increase as fruit matured from the “green” to the “white” to the “pink” stage. Appreciable injury (more than two unpigmented drupelets per fruit) only occurred at 42C and higher with 4 or more hours of UV radiation at the fluence level used. While the injury at 42C was proportional to UV exposure, the radiation environment in the laboratory was not designed to simulate solar radiation. Therefore, no quantitative function relating injury to fruit temperature and UV radiation is presented. The results indicated that attenuating UV absorption alone, without lowering temperature, is likely to protect raspberries in the field.
The pH of processing tomato at harvest is a key quality criterion and is critical for safe product storage. Maximum allowable fruit homogenate pH is often 4.5. Our objective was to quantify the influence of air temperature on pH, including any interaction with either fruit age or use of ethephon. Three planting dates were imposed as main treatments and ethephon as a subtreatment in a field trial, and each planting was harvested on four dates. Fruits were harvested from trusses tagged to identify three fruit age groups in sub-subplots. Temperature exerted primary control of tomato pH. The relationship of bulk fruit pH to thermal time was curvilinear (pH was always <4.55); however, when pH was related to thermal time from anthesis, a linear relationship resulted. The oldest fruit had a much higher pH (>4.5) than younger ones (mean pH for all dates = 4.3). Ethephon did not alter these temperature/pH relationships.
Abstract
‘Olympus’ strawberries (Fragaria × ananassa (Duch.) with and without black polyethylene mulch were compared in terms of leaflet elongation and diurnal water potential (ψ) of leaves at 2 levels of drip irrigation. Mulch increased leaflet elongation at both irrigation levels, but had no appreciable effect on soil water potential at 20 cm depth, nor on leaf ψ or leaf turgor. Leaflet elongation with black polyethylene may have been favored by the increased soil temperature throughout the upper 20 cm. At the 10-cm depth, mulched, high-moisture soil was an average of 3.0°C warmer during a diurnal cycle. Greatest warming was in late afternoon and late evening in low and high moisture soil, respectively.
Abstract
Two field plantings of strawberries [Fragaria × ananassa Duch. cv. Olympus] were grown with and without black polyethylene mulch at 3 levels of drip irrigation and differential irrigation was maintained after plant establishment for 1 month in 1977 and 2 months in 1978. During the driest portion of each year the soil water potential at 20 cm depth remained above −0.5 bars for the highest level of irrigation, and fell below −11 bars at the lowest level. Mulch conserved soil moisture at the 2 lower irrigation levels in 1977, but this effect was minor in 1978. Vegetative growth was increased by both irrigation and mulch. The number of leaves produced during the first growing season was 30% (1977) and 25% (1978) greater in the high than the low-irrigation regime. Mulching improved leaf production 27% (1977) and 14% (1978). Most of these vegetative differences between treatments were still apparent at fruit harvest the following July. During a second year of treatments on the 1977 planting, the number of leaves was further enhanced by mulch and high irrigation. At the subsequent fruit harvest, 2-year-old plants had more leaves than those 1 year old, but the leaf area per plant averaged 27% lower. Leaf and crown dry weights of either 1- or 2-year-old plants at fruit harvest were slightly greater due to irrigation and significantly higher due to mulch, whereas root dry weight was unaffected by either treatment. The amount of summer irrigation required to sustain vigorous vegetative growth in mulched plants was only one third that of unmulched strawberries.
Abstract
Strawberries [Fragaria × ananassa Duch. cv. Olympus] were planted in 2 successive years and grown at 3 levels of drip irrigation, with and without polyethylene mulch. Differential irrigation was applied only during 1 (1977) or 2 (1978) months during the summer and all treatments were irrigated equally during the following spring. In both summers, the soil water potential at 20-cm depth was maintained above −0.5 bars for the highest level of irrigation and fell below −11 bars at the low level. Mulch conserved soil moisture at the 2 lower irrigation levels in 1977, but this effect was nearly absent in 1978 conditions. The highest irrigation regime had about 22% more flowers and 18% more fruit than the lowest regime in the spring of the first harvest season in both plantings. Mulch only increased flowering in the 1977 planting (12%), whereas the number of fruit was increased about 11% by mulch in both plantings. The high yield capacity of ‘Olympus’ was confirmed (37.8 MT/ha). Mulch increased the yield of the 1978 planting 18%, despite its lack of effect on the number of flowers in that year. This suggests a spring influence on yield. The highest irrigation regime out-yielded the lowest regime by 13% in the first crop of both plantings, although this increase was significant only in the 1977 planting. The second year crop of the 1977 planting yielded 21% less than the first year, and failed to show significant treatment differences in flower number or fruit yield despite much larger plant size with mulch and higher irrigation levels. The yield component which showed the greatest decline between years was the percentage fruit set. In general, mulch and greater summer irrigation increased fruit yield less dramatically than they enhanced vegetative growth. However, the 13% to 18% increases may represent a significant economic gain because the typical yield of ‘Olympus’ is much higher than other Pacific Northwest cultivars. Mulch also produced a greater water use efficiency.
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.
Seasonal water use data are presented for 4-year-old Pyrus serotina Rehder cv. Hosui growing in drainage lysimeters and trained onto a Tatura trellis. Weekly water use (WU) was calculated using the mass balance approach. For 8 consecutive weeks during late summer, instantaneous WU was also measured by the compensation heat-pulse technique for measuring sap flow. Although good agreement was found between the two methods for 4 weeks after probe installation, discrepancies increased after this time. Water use was highest in early to mid-January in New Zealand, averaging ≈8 liters/tree per day, or 2 liters·m-2 canopy surface area/day. Total water use over the growing season was 1070 liters/tree, or 245 liters·m-2 canopy surface area. The correlation coefficient between weekly WU and evaporation from a nearby Class A pan was 0.81 for the season. Weekly crop coefficients thus calculated for the well-watered trees ranged from 0.15 to 0.55 and 0.20 to 0.83 when calculated using canopy surface area and projected ground area, respectively. Low values were due to low values of canopy leaf area early in the season. Withholding irrigation during three periods resulted in a gradual decline in water use. Water-stressed trees had a lower predawn water potential than fully irrigated trees. This pattern was followed by a more-rapid decline during the morning, and a slower recovery during late afternoon and early evening. Midday leaf water potential never fell below -2.5 MPa.
Stomatal conductance (g s) of `Hosui' Asian pear (Pyrus serotina Rehder) trees growing in lysimeters was characterized for trees in well-watered soil and after brief water deficit. The measures of water status used to interpret g s data were soil-water content, leaf water potential (ψl), and instantaneous water use (trunk sap flow by the compensation heat-pulse technique). The diurnal course and range of g s values of well-irrigated Asian pear trees were similar to those reported for other tree fruit crops. Soil moisture at the end of a midsummer deficit period was 60% of lysimeter pot capacity, and diurnal ψl reflected this deficit predawn and in the late afternoon compared to well-irrigated trees. The g s was sensitive to deficit irrigation during more of the day than ψl, with g s values <3 mm·s-1 for most of the day; these were less than half the conductances of well-irrigated trees. The reduction of g s in response to a given soil-water deficit was not as great on days with lower evaporative demand. After a water deficit, g s recovered to predeficit values only gradually over 2 to 3 days. The low g s of trees in dry soil was the apparent cause of reduced transpiration, measured by trunk sap flow, and reduced responsiveness of sap flow to fluctuations in net radiation.