Search Results

You are looking at 1 - 10 of 75 items for :

  • evapotranspiration x
  • Journal of the American Society for Horticultural Science x
Clear All

Abbreviations: ET, evapotranspiration; ψ, water potential; VPD, vapor pressure deficit. 1 UC Cooperative Extension, 733 County Center III Court, Modesto, CA 95355. This work supported in part by a grant from the California Prune Board. The cost of

Free access

Abbreviations: A, alfalfa; CWSI, crop water stress index; CTV, canopy-temperature-variability; D, drainage; ET, evapotranspiration; FI, full irrigation; H, herbicide strip; I, irrigation, IR, infrared P, black plastic mulch; R n , net radiation; SDD

Free access

The use of potential evapotranspiration (PET) estimates to identify irrigation timing for greenhouse tomatoes (Lycopersicon esculentum Mill.) grown in peat-based substrate was evaluated for a spring and fall crop. PET (using the Penman equation) was calculated from leaf, wet and dry bulb temperatures, and incident and reflected photosynthetic photon flux. Substrate matric potential (SMP) was monitored continuously using electronic tensiometers. Two irrigation starting setpoints (-4.5 and -6.5 kPa SMP) and two nutrient solution electrical conductivity (EC) treatments (1.5 and 3.0 dS·m-1) were factorially combined in a completely randomized design. Irrigation frequency was greater in treatments irrigated at -4.5 than at -6.5 kPa. The integral of calculated PET values was correlated with SMP for both experiments. Accumulated PET values were higher at the start of irrigation in the -6.5-kPa treatments for spring and fall crops. Nutrient solution EC did not influence irrigation frequency. Leaf pressure potential (LPP) was correlated to PET-predicted LPP (r 2 > 0.56) in plants subjected to high EC, low (-6.5 kPa) matric potential setpoint, or both treatments. PET and electronic tensiometer technology can be used jointly to improve irrigation management for tomatoes grown in peat-based substrates by more accurately responding to crop needs for water and nutrients.

Free access

A 2-year study was conducted to quantify the actual evapotranspiration (ETa) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ETa/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ETa was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ETa were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ETa. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.

Free access

The influence of K nutrition (25, 75, 150, 300, 450, and 600 mg K/liter) and moisture stress conditioning (MSC) (exposing plants to four sublethal dry-down cycles) on leaf water relations, evapotranspiration, growth, and nutrient content was determined for salvia (Salvia splendens F. Sellow `Bonfire'). Potassium concentration and MSC had an interactive influence on osmotic potential at full (π100) and zero (π0) turgor. Differences in osmotic potential between MSC and non-MSC plants for π100 and π0 increased with increasing K concentration. Increasing K concentration and MSC resulted in active osmotic adjustment and, consequently, increased cellular turgor potentials. Foliar K content increased with increasing K concentration and MSC. High K concentrations and MSC both reduced plant evapotranspiration on a per-plant and per-unit-leaf-area basis. Greatest shoot dry weight occurred for plants grown with 300 mg K/liter and non-MSC. Total leaf area increased with increasing K concentration, but MSC had little effect.

Free access
Author:

Three species of woody ornamentals, Viburnum odoratissimum Ker Gawl, Ligustrum japonicum Thunb., and Rhaphiolepis indica Lindl. were transplanted from 3.8-L into 11.4-L containers and grown for 6 months while irrigated with overhead sprinkler irrigation. Irrigation regimes imposed consisted of an 18-mm-daily control and irrigation to saturation based on 20%, 40%, 60%, and 80% deficits in plant available water [management allowed deficits (MAD)]. Based on different evaluation methods, recommendations of 20%, 20%, and 40% MAD are supported for V. odoratissimum, L. japonica, and R. indica, respectively, for commercial production. Comparisons of plant growth rates, supplied water, and conversion of transpiration to shoot biomass are discussed among irrigation regimes within each species. Comparisons of cumulative actual evapotranspiration (ETA) to either shoot dry mass or canopy volume were linear and highly correlated. Results indicated there were minimum cumulative ETA volumes required for plants to obtain a specific size. This suggests that irrigation regimes that restrict daily ETA will prolong production times and may increase supplemental irrigation requirements. Thus the hypothesis that restrictive irrigation regimes will reduce irrigation requirements to produce container plants is false due to the strong relationship between cumulative ETA and plant size.

Free access

Abstract

Sweet corn (Zea mays L.) was irrigated using randomized complete block and line source experimental designs in 1984 and 1985 on a mixed, mesic Cumulic Ultic Haploxeroll soil. Irrigations were scheduled when ≈50% of the available water was depleted in the root zone of the 100% treatment to refill the root zone to 0% to 100% of field capacity (five irrigation levels). Four yield parameters were measured for all plots: yield of all ears before husking, yield of good husked ears, kernel yield (fresh), and total dry matter production of plants and ears. Maximum relative total unhusked ear yield and near-maximum evapotranspiration (ET) were obtained at 85% of maximum water applied, indicating that high yields can be maintained with deficit irrigation. Without irrigation, only 44% of maximum yield was obtained. Maximum water use efficiency (WUE), defined as the total unhusked ear yield in kg·ha−1·mm−1ET, occurred between 407 and 418 mm of ET. The maximum WUE corresponded to ≈313 mm water applied (WA); maximum yield, however, occurred within the range of 449 to 518 mm WA. Irrigation treatments to achieve maximum WUE were predicted to result in a 10% yield reduction.

Open Access

Cabbage (Brassica oleracea L.) was grown in drainage lysimeters under controlled soil water regimes during 3 years. Three irrigation regimes were imposed on cabbage grown on two soil types during the spring and fall growing seasons. Irrigation regimes consisted of applying water when the soil water tension at 10 cm exceeded 25, 50, or 75 kPa during crop growth. Yields and water use were highest when irrigation was applied at 25 kPa soil water tension. Regression equations are presented to describe the relationships of water use to plant age and to compute the ratios of daily evapotranspiration to pan evaporation (crop factors) for cabbage grown under the three irrigation regimes.

Free access

`Keystone Resistant Giant' bell pepper (Capsicum annuum L.) was grown in drainage lysimeters under controlled soil water regimes during 1982, 1984, and 1985. Three irrigation regimes were imposed on bell pepper grown on two soil types during spring and fall growing seasons. Irrigation regimes consisted of applying water when the soil water tension at 10 cm exceeded 25, 50, or 75 kPa during crop growth. Yields and water use were greatest when irrigation was applied at 25 kPa. Regression equations are presented to describe the relationships of water use to plant age and to compute the ratios of daily evapotranspiration to pan evaporation (crop factors) for bell pepper grown under the three irrigation regimes.

Free access

Abstract

Summer squash (Cucurbita pepo L. cv. Dixie hybrid) were grown in drainage lysimeters under closely controlled and monitored soil water regimes. Variables included three irrigation treatments, three growing seasons, and two soil types. Marketable fruit yield was greatest and production cost per kilogram of marketable fruit was least when squash was irrigated at 25 kPa of soil water tension. Yields were greatest for the spring season of production and least for the fall season. Regression equations are provided to describe the relationships of water use to plant age and to compute daily evapotranspiration : pan evaporation ratios (crop factors) for squash irrigated at 25, 50, and 75 kPa of soil water tension during the spring, summer, or fall production season.

Open Access