Search Results
Abstract
Plants of onion (Allium cepa L.) grown in the greenhouse and field were treated with antitranspirants during the bulb enlargement stage of growth. Daily water use in the greenhouse was significantly reduced by 1% Vapor Gard (di-1-p-menthene) and 3% Folicote (parafin wax) emulsions. The 3% Folicote treatment reduced bulb yield. In field studies, Folicote increased bulb size and total yield by 1.5–4.2 MT/ha. The increased yields resulted from larger bulb size, presumably due to reduction in the degree of moisture stress between irrigations. Neutron probe readings indicated a reduction in the rate of water removal from soils (30 cm depth) and an increase in bulb size and total yield in plots treated with the antitranspirants Folicote and tallow.
Freeze losses to grapes in March, after mild deacclimatizing winters, is the major production risk on the Texas High Plains. Earlier studies indicated the effectiveness of evaporative cooling in reducing grape bud heat summation with a correlated delay in budbreak. Parameters relating to water-use-efficiency were identified. In the current study, these parameters were incorporated to minimize water use. Water was applied through microjets for 25 seconds every 4 minutes any time air temperature exceeded 10°C, 15°C, and Control. Bud temperatures were monitored continuously by thermocouples and data logger, and correlated with budbreak and plant development. Random bud samples were taken weekly prior to budbreak and subjected to differential thermal analysis. A freeze on March 23 (-3.5°C) resulted in differential primary bud losses to Chardonnay during budbreak, and to Cabernet Sauvignon 15 days prior to budbreak. Evaporative cooling significantly increased yields in both cultivars. Differential thermal analysis verified differences in cold stress tolerance in Chardonay prior to budbreak.
Mild temperatures during late winter have caused early budbreak in grapes which resulted in freeze injury and significant crop losses in 1980 and 1988. Evaporative cooling of grapevines with microsprinklers when the air temperature exceeded 10 °C (50 °F) used 100 liters/min/hectare of treated grapes (11 gallons/min/acre) and delayed budbreak for a period of 7 to 10 days. Methods of reducing the amount of water used while not reducing the cooling were evaluated. The average hourly difference between wet and dry bud temperatures, measured with thermocouples, were summed during the system operation time and compared as a function of air temperature, wind speed, global radiation, and relative humidity limits. Limiting the cooling system operation time as a function of air temperature, wind speed, or global radiation reduced cooling efficiency by approximately a one to one ratio. Limiting system operation to humidities less than 60% reduced the amount of water used by 33%, with only a 9% reduction in cooling efficiency. By changing the wetting interval employed in this research from 25 seconds every three minutes to 25 seconds every four minutes, total water conservation would increase to 50% with insignificant changes in cooling efficiencies. These system modifications would reduce water application requirements to 50 liters/min/hectare of grapes (5.5 gallons/minute/acre).
Mild temperatures during late winter have caused early budbreak in grapes which resulted in freeze injury and significant crop losses in 1980 and 1988. Evaporative cooling of grapevines with microsprinklers when the air temperature exceeded 10 °C (50 °F) used 100 liters/min/hectare of treated grapes (11 gallons/min/acre) and delayed budbreak for a period of 7 to 10 days. Methods of reducing the amount of water used while not reducing the cooling were evaluated. The average hourly difference between wet and dry bud temperatures, measured with thermocouples, were summed during the system operation time and compared as a function of air temperature, wind speed, global radiation, and relative humidity limits. Limiting the cooling system operation time as a function of air temperature, wind speed, or global radiation reduced cooling efficiency by approximately a one to one ratio. Limiting system operation to humidities less than 60% reduced the amount of water used by 33%, with only a 9% reduction in cooling efficiency. By changing the wetting interval employed in this research from 25 seconds every three minutes to 25 seconds every four minutes, total water conservation would increase to 50% with insignificant changes in cooling efficiencies. These system modifications would reduce water application requirements to 50 liters/min/hectare of grapes (5.5 gallons/minute/acre).
The major production risk for grapes on the Texas High Plains is freeze injury to buds and wood due to deacclimation brought about by warm periods in late winter. Delaying plant development by any means would reduce risk from injury. Reducing cumulative heat summation between rest and bloom has resulted in delayed bloom on peaches but internal rest is not expressed in grapes. An evaporative cooling system using microsprinklers was applied to a Cabernet Sauvignon vineyard during Jan.-April 1989. The system provided a 25 second wetting period at 3 minute intervals anytime air temperatures exceeded 10° C. Bud temperatures were monitored continuously with a data logger and correlated to cumulative budbreak and plant development. Significant bud cooling was achieved and by normal budbreak cooled buds lagged uncooled buds by 72% in degree days. A similar lag in budbreak was recorded early with some cooled buds breaking 3 weeks after most uncooled buds were open. Cooled plants continued to lag uncooled plants at bloom and even at harvest where oBrix and pH were lower and total acids higher from cooled plots.