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Abstract

Evapotranspiration of two 5-year-old mature trees of peach [Prunus persica (L.) Batsch] was measured in weighing lysimeters. Diurnal water use patterns were conventional. Trees used an average of 136, 114, 96, and 61 liters per day in July, August, September, and October respectively, with an overall daily average of 102 liters. The crop coefficient based on class A pan evaporation declined from 0.98 in early July to 0.40 just before leaf fall and averaged 0.71 for the season. Class A pan evaporation correlated well with evapotranspiration on a weekly average but poorly on a daily basis.

Open 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

Green roofs are an increasingly common, environmentally responsible building practice in the United States and abroad. They represent a new and growing market for the horticulture field, but require vegetation tolerant of harsh environmental conditions. Historically, Sedum species have been the most commonly used plants because, with proper species selection, they are tolerant of extreme temperatures, high winds, low fertility, and a limited water supply. A greenhouse study was conducted to determine how water availability influences growth and survival of a mixture of Sedum spp. on a green roof drainage system. Results indicate that substrate volumetric moisture content can be reduced to 0 m3·m–3 within 1 day after watering depending on substrate depth and composition. Deeper substrates provided additional growth with sufficient water, but also required additional irrigation because of the higher evapotranspiration rates resulting from the greater biomass. Over the 88 day study, water was required at least once every 14 days to support growth in green roof substrates with a 2-cm media depth. However, substrates with a 6-cm media depth could do so with a watering only once every 28 days. Although vegetation was still viable after 88 days of drought, water should be applied at least once every 28 days for typical green roof substrates and more frequently for shallower substrates to sustain growth. The ability of Sedum to withstand extended drought conditions makes it ideal for shallow green roof systems.

Free access

A 3-year study was conducted in central California to compare the effects of furrow, microjet, surface drip, and sub surface drip irrigation on vegetative growth and early production of newly planted `Crimson Lady' peach [Prunus persica (L.) Batsch] trees. Furrow treatments were irrigated every 7, 14, or 21 days; microjet treatments were irrigated every 2-3, 7, or 14 days; and surface and subsurface drip (with one, two, or three buried laterals per row) treatments were irrigated when accumulated crop evapotranspiration reached 2.5 mm. The overall performance showed that trees irrigated by surface and subsurface drip were significantly larger, produced higher yields, and had higher water use efficiency than trees irrigated by microjets. In fact, more than twice as much water had to be applied to trees with microjets than to trees with drip systems in order to achieve the same amount of vegetative growth and yield. Yield and water use efficiency were also higher under surface and subsurface drip irrigation than under furrow irrigation, although tree size was similar among the treatments. Little difference was found between trees irrigated by surface and subsurface drip, except that trees irrigated with only one subsurface drip lateral were less vigorous, but not less productive, than trees irrigated by one surface drip lateral, or by two or three subsurface drip laterals. Within furrow and microjet treatments, irrigation frequency had little effect on tree development and performance with the exception that furrow irrigation every 3 weeks produced smaller trees than furrow irrigation every 1 or 2 weeks.

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Abstract

The effects of different plastic mulching using drip irrigation on yields, soil temperature, crop water requirements, and root density and distribution were determined for muskmelon (Cucumis melo L.) at the Jordan Valley Research Station, Jordan. There were no significant differences among transparent, black, and nonmulched treatments with respect to irrigation amounts, soil moisture depletion, total water supplied, deep percolation losses, and vapotranspiration. Root weights, density, and distribution, horizontally and vertically, were not significantly different among treatments. Transparent mulch treatment yields averaged 14.2 t·ha-1 and were significantly lower (5% level) than average yields (28.7 t·ha-1) of the black mulch treatments. Nonmulched treatment yields averaged 6.0 t·ha-1 and were significantly different from the average transparent mulch (5% level) and from black mulch (1% level). This difference in yield may be attributed to the fact that black mulch treatments received more irrigations than transparent mulch and bare ones. Calculations of expected potential evapotranspiration for muskmelon during the season showed that the plants did not receive their water requirements.

Open Access

Leaf gas exchange of six red raspberry (Rubus idaeus L.) and one blackberry (Rubus L. subgenus Rubus Watson) genotypes growing in 12-L containers was measured at four temperatures (20, 25, 30, and 35 °C) once a month for 3 months in growth chambers by infrared gas analysis. Measurements were taken on three successive leaves on the same primocane between the third and seventh nodes (≈75% to 85% of full leaf expansion). The plants were grown in ambient (field) conditions except when measurements were taken. Maximum daily ambient temperatures rose as high as ≈37 °C during this period. Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (gs ) were measured during June, July, and August. Significant differences (P ≤ 0.01) in A were found among the seven genotypes. 'Arapaho' blackberry displayed the highest mean A rate at all temperatures. Only in the raspberry cultivars Nova and Reveille did the rate of A drop significantly when temperature increased from 20 to 30 °C. 'Reveille' was also the only cultivar in which A significantly declined between 30 and 35 °C. The ET increased significantly over the four temperatures in four cultivars ('Arapaho', 'Heritage', 'Nova', and 'Southland'). The ET rate at 35 °C was higher for 'Arapaho' than for all other cultivars. 'Autumn Bliss', 'Dormanred', and 'Reveille' did not change significantly as the temperature rose from 20 to 35 °C. Stomatal conductance of 'Heritage' and 'Arapaho' did not change significantly between 20 and 35 °C, whereas that of 'Autumn Bliss' and 'Reveille' declined almost 50% when temperature increased to 30 or 35 °C.

Free access

Research was conducted to assess the response of tall fescue (Festuca arundinacea Schreb.) to water deficit conditions. Different leaching fractions (LF = drainage volume/irrigation volume) and irrigation frequencies (IF) were imposed over a 119-day summer period in Las Vegas, Nevada, followed by a 71-day recovery period. Plots of tall fescue contained 120 cm deep × 51 cm diameter draining lysimeters. Irrigations were based on an evapotranspiration (ET) feedback system to establish LFs of +0.15, 0.00, -0.15, -0.25, and -0.40. Plots were irrigated on a daily or twice per week schedule. N was applied to subplots at a rate of 0, 12.2, or 24.4 kg·ha-1 per month. As LF decreased, relative soil water in storage declined in a linear fashion (r 2 = 0.97, P = 0.001). Storage depletions for the four lowest LFs at the end of 119 days of imposed water deficits were about 15%, 40%, 60%, and 70% compared to the +0.15 LF treatment. Canopy temperature, soil matric potential (Ψm), leaf xylem water potential (ΨLX), leaf stomatal conductance (gs), clipping yield, color and cover ratings all statistically separated (P < 0.05) based on LF but not on IF. However, irrigation amount (I), ET, tissue moisture content and total Kjeldahl N (TKN) separated based on LF and IF with a significant LF by IF interaction for I (P < 0.05) and TKN (P < 0.001). An irrigation savings of 60.4 cm was realized during the 119-day water deficit period at the -0.40 LF. However, at the lower LFs, plant stress increased (all parameters) with color ratings declining below an acceptable value of 8.0. An Irrigation/Potential ET (I/ETo) threshold of 0.80 was determined for both color and cover. After a 71-day recovery period both color and cover returned to pre experimental values at the two higher N rates. Results of this experiment indicate that implementing a twice weekly irrigation strategy at a -0.15 LF on tall fescue during summer months in an arid environment would lead to savings of 37.5 cm of water while still maintaining acceptable color and cover ratings.

Free access

Abstract

The crop water stress index (CWSI) may be useful for optimal irrigation timing. This preliminary study evaluates the relationships between the CWSI and evapotranspiration (ET) and yield. The CWSI was also characterized on an hourly basis. Once-daily CWSI measurements after full ground cover was established and hourly CWSI measurements on 4 days were made in sweet corn (Zea mays L. ‘Jubilee’) irrigation experiments in 1984 and 1985. The gradient of water applied included five irrigation levels established from 0% to 100%, with the 100% level intended to refill the root zone to field capacity, after 50% depletion of available water, at each irrigation. CWSI values, obtained hourly throughout the day, were highest between 1000 and 1700 hr. CWSI values tended to be higher in the less-irrigated plots (40% and less) than in those that received greater amounts of water (57% to 100% treatment levels). Seasonal average CWSI values (midday measurements) were closely related to the seasonal ET deficit (r 2 ranged from 0.45 to 0.96), but there was not the expected 1:1 relationship of CWSI and ET deficit. The yield deficit of good, husked ears was also closely related to CWSI (r 2 ranged from 0.82 to 0.93), but differences in these relationships between years and experiments indicate that CWSI measurements must be improved.

Open Access

initiated when crowns broke dormancy and leaves were fully emerged; drip irrigation [25%, 50%, and 100% of daily pan evapotranspiration rate (PET)], and nitrogen (N) fertilizer [0, 4.6, and 9.2 kg/ha as Ca(NO 3 ) 2 ]. Water volume applied to each treatment

Free access

Abstract

Air layers from 6 blight-affected and 6 healthy grapefruit, Citrus paradisi Macf., trees were grown in a greenhouse with low N, low S, and lime and high N, high S, and no lime regimes, one air layer from each tree in each treatment. Shoot fresh weight of air layers from healthy trees was 25%, and root fresh weight was 38% greater than that of air layers from blighted trees, after 8 months of treatment (shoot/root ratios of 1.59 and 1.90). Shoot weight was the same with both nutrient treatments; root weight was 40% smaller with high N, high S, and no lime than with low N, low S, and lime (shoot/root ratios of 2.12 and 1.37). Air layers from blighted trees had higher concentrations of N, P, and water-soluble phenolics, and lower Ca and Na in the wood; more S, Fe, Zn, Cu, and Mo in the bark; more N and K, and less Mg, Na, and Cl in the roots, and more P and less B and Cl in the leaves than air layers from healthy trees. Low N, low S, and lime induced higher K and Mo in the wood, higher K in the bark, and lower Na and Cl in the roots of air layers from blighted trees; high N, high S, and no lime increased Mg and Zn in the roots, Fe in the wood, and Zn in the leaves of air layers from blighted trees above the levels of healthy air layers. There were curvilinear relationships between evapotranspiration and root weight and the shoot/root ratio; air layers from blighted trees transpired more water than those from healthy trees on a per unit shoot and root weight basis.

Open Access