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Fabián Robles-Contreras, Rubén Macias-Duarte, Raul Leonel Grijalva-Contreras, and Manuel de Jesus Valenzuela-Ruiz

The sabila plant is considered a strategic crop for the arid and semi-arid lands of Mexico, because it can be a high water-efficient crop due to its low water requirements, and is currently developing satisfactorily on an experimental scale in the agricultural area of Caborca, Sonora, Mexico, in the Sonoran Desert. This agricultural zone is characterized by a sandy soil with little or no organic matter and limited water supplies. Research consisted of evaluating the effect of bovine manure (BM) application to soil on the yield and size of sabila leaves. A sabila planting was established in Summer 2002, with a density of 15,000 plants/ha. Two applications of BM (9 t·ha-1) were made, one at planting time in Aug. 2002, and another one in Feb. 2003. BM was not applied to the control treatment. Although the harvest of leaves initiated in Dec. 2003 (plant formation), the first commercial harvest was made in Jan. 2005. We measured the yield and the average weight of leaves. The results indicated statistical differences (0.05) and an increase in the yield of 12.2 t·ha-1, which represents 26% more with the BM application with respect to the control, which produced 47.1 t·ha-1. As far as the average weight of leaves, there were no statistical differences between the BM application (597 g) and the control (532 g), although in both cases, they met the standards demanded by companies that manufacture products with sabila.

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Jayne M. Zajicek, Nowell J. Adams, and Shelley A. McReynolds

Landscape plantings have been designed traditionally using aesthetic criteria with minimal consideration given to water requirements. The primary objective of this research was to develop quantitative information on water use of plant communities conventionally used in urban landscapes. Pots of Photinia × Fraseri (photinia Fraseri), Lagerstroemia indica 'Carolina Beauty' (crape myrtle), or Ligustrum japonicum (wax leaf ligustrum) were transplanted from 3.8 l into 75.7 l pots with either Stenotaphrum secundatum 'Texas Common' (St. Augustinegrass), Cynodon dactylon × C. transvallensis 'Tiffway' (bermudagrass), Trachelospermum asiaticum (Asiatic jasmine), or left with bare soil. Whole community water use was measured gravimetrically. In addition, sap flow rates were recorded for shrub species with stem flow gauges. Sap flow measurements were correlated to whole community water use recorded during the same time intervals. Whole community water use differed due to the groundcover component; bermudagrass, Asiatic jasmine, and bare soil communities used less water than St. Augustinegrass communities. Differences were also noted in stomatal conductance and leaf water potential among the species.

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Fabián Robles-Contreras, Raul Leonel Grijalva-Contreras, Manuel de Jesus Valenzuela-Ruiz, and Rubén Macias-Duarte

Water is a very limited resource in the Sonoran Desert region of Caborca, Sonora, Mexico. For an efficient use of irrigation water, a method of calculating water requirements of the crops is needed. Potential evapotranspiration (Eto) value obtained with the Penman-Monteith model from a regional weather station was not dependable, since some parameters, such as sensible heat flux in the soil, are estimated from a fixed rate with net radiation (Rn), also an estimated value. The weather station did not have a sensor for heat flux in its network. Studies in northwestern Mexico have indicated that it is feasible to adapt the use of the Makkink model, because a single measurement of solar radiation and temperature would be required. We compared the daily Makkink Eto against the Class A pan method (control) Eto during 75 days and found a value of 0.81 mm/day less with the Makkink model. To fit the Makkink model to regional conditions, we ran the Makkink model varying the value of C constant (from 0.5 to 0.95), and found that a value of C = 0.87 substituted for C = 0.65 (original value) has an daily average difference of 0.09 mm/day less with respect to the control. This could be because there are few clouds in the region, and a greater proportion of global radiation arrives at the surface from the earth or the crops in form of net radiation.

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David A. Bender, Roland E. Roberts, and Frank J. Dainello

Watermelon is grown under a range of moisture regimes from rainfed to heavily irrigated, but water requirement patterns are not well documented. Drip irrigation and plastic mulch provide the opportunity to control water applications to optimize yield and quality. Water applied through subsurface drip irrigation was measured in two watermelon trials in 1998 (25 seeded and 20 seedless cultivars) and 1999 (26 seeded and 14 seedless cultivars) at Lubbock, Texas. Melons were transplanted in plastic-covered raised beds 13.6 m long spaced 2 m apart. Irrigation was applied when morning soil moisture tension measured by tensiometers exceeded 20 kPa. Watermelon yields ranged from 50 to 100 t·ha-1 with excellent quality. Weekly water use averaged 14 mm during the first 3 weeks of establishment then increased to 28 mm during the next 3 weeks as plants were running and blooming. During the 5-week fruit-enlargement period, water uptake averaged 57 mm, then decreased as full fruit size was attained. Similar uptake patterns in both years suggest that meaningful crop coefficients for scheduling watermelon irrigation could be based on phenological growth stages.

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C.M. Geraldson

A gradient concept was initiated and evaluated at the Gulf Coast Research and Education Center, Bradenton, during the 1960s as the nutritional component in a full-bed mulch system of production. Commercial tomato yields in Florida more than doubled with the shift to the gradient-mulch system. Conventionally, nutrients move to the root in the water by mass flow and thus are a function of water requirement. With the soil as the buffer component, nutrient input may or may not be synchronized with root removal. Movement with the gradient is by diffusion and the nutrient/water input is synchronized with rate of removal by the root. The limited buffer potential of the soil is replaced by the gradient with an unlimited buffer potential. Production in the field or a container has a maximum potential with the gradient procedure but can become limited in the field and a failure in the container with conventional procedure. The gradient requires minimal soil (a framework for the gradient) uses minimal water, creates minimal pollution, requires minimal management and provides a nutritional stability that has an unlimited productivity potential. The N–K banded on the soil bed surface in conjunction with a continuing water supply are the basic parameters of the gradient concept.

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Anthony S. Davis, Matthew M. Aghai, Jeremiah R. Pinto, and Kent G. Apostol

Because limitations on water used by container nurseries has become commonplace, nursery growers will have to improve irrigation management. Subirrigation systems may provide an alternative to overhead irrigation systems by mitigating groundwater pollution and excessive water consumption. Seedling growth, gas exchange, leaf nitrogen (N) content, and water use were compared between overhead irrigation and subirrigation systems used to produce trembling aspen (Populus tremuloides Michx.) seedlings. After 3 months of nursery culture, subirrigation resulted in a 45% reduction in water use compared with overhead irrigation. At the end of the growing season, subirrigated seedlings had lower net photosynthetic assimilation, stomatal conductance (g S), and leaf area, indicating earlier leaf senescence. However, no significant differences were detected for biomass, leaf N content, height, root-collar diameter, or root volume. Thus, we suggest that subirrigation systems offer promising potential for aspen seedling production when compared with overhead irrigation given the added benefits of water conservation and reduced nutrient runoff. Continuing emphasis on refinement such as determining the plant water requirements based on growth and development as well as container configuration is needed so that the intended benefits of using subirrigation can be realized.

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Xin Zhao and Edward E. Carey

High tunnels, unheated greenhouses, have been shown to be a profitable season-extending production tool for many horticultural crops. Production of cool-season vegetables during hot summer months can be achieved using shaded high tunnels. Microclimate in high tunnels and open field was monitored during summer trials of leaf lettuce, in which unshaded tunnels and shaded tunnels (39% PAK white shadecloth) were used, respectively, in 2002 and 2003. Wind speed was consistently lower in high tunnels. Compared to open field, daily air temperature was about 0.7 °C higher in unshaded high tunnels, and 0.5 °C lower in shaded high tunnels. Relative humidity was slightly lower in unshaded tunnels, but tended to increase in shaded tunnels, in comparison to the open field. When using shadecloth, soil temperature was lowered by 1∼3 °C and the leaf surface temperature was significantly reduced by 1.5∼2.5 °C. In shaded high tunnels, PAR light dropped by at least 50% relative to the outside, where the maximum PAR light intensity reached 1800 μmol·m-2·s-1. Overall, shaded high tunnels resulted in higher quality lettuce, with less bolting and bitterness. Reference crop evapotranspiration (ET0) was estimated from meteorological data on a daily basis using the FAO-56 method. ET0 was lowest in shaded high tunnels, and highest in the open field. Relatively lower ET0 in high tunnels indicated a likely lower water requirement and therefore improved water use efficiency compared with the open field.

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Giovanni Piccinni, Thomas Gerik, Evelyn Steglich, Daniel Leskovar, Jonghan Ko, Thomas Marek, and Terry Howell

Improving irrigation water management for crop production is becoming increasingly important in South Texas as the water supplies shrink and competition with urban centers in the region grows. Crop simulators and crop evapotranspiration (ET) are appealing methods for estimating crop water use and irrigation requirements because of the low investment in time and dollars required by on-site (in-field) measurement of soil and/or crop water status. We compared the effectiveness of the Crop.m.an/EPIC crop simulator and Crop-ET approaches estimating the crop water use for irrigation scheduling of spinach. In-ground weighing lysimeters were used to measure real-time spinach water use during the growing season. We related the water use of the spinach crop to a well-watered reference grass crop to determine crop coefficients (Kc) to assist in predicting accurate crop needs using available meteorological data. In addition, we ran several simulations of CropMan to evaluate the best management for growing spinach under limited water availability. Results show the possibility of saving about 61 to 74 million m3 of water per year in the 36,500 ha of irrigated farms of the Edwards aquifer region if proper irrigation management techniques are implemented in conjunction with the newly developed decision support systems. We discuss the implications of the use of these technologies for improving the effectiveness of irrigation and for reducing irrigation water requirements in South Texas.

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Fabián Robles-Contreras, Rubén Macias-Duarte, Raul Leonel Grijalva-Contreras, and Manuel de Jesus Valenzuela-Ruiz

The agricultural zones in the Sonoran Desert have great problems of water availability. An alternative that the grower must consider to diminish the negative effects caused by the water shortage is the establishment of crops with low water requirements. One such crop is the cactus pear vegetable (nopalitos). This crop supports and produces in conditions of low water availability and is a product of high demand. The objective was evaluate the potential of production of nopalitos under this condition. We evaluated two cultivars (Opuntia inermis and O. Ficus-indica) in a system of furrows with 1 m of separation between lines and 50 cm between plants, with a pruninig system of two producing caldodes per plant. The plot was drip-irrigated every 10–15 days. The evaluation was made during Spring 2004, harvesting the nopalitos to commercial size (17–21 cm) every 3–4 days. The measured variables were the yield and the weight of the nopalitos. The budbreak and harvest of nopalitos appeared in form of productive cycles, and we evaluated only the first two cycles of harvest (24 Mar. to 20 May). The obtained yields were 45.8 and 42 t·ha-1 in cv. Opuntia inermis and O. ficus-indica, respectively. The weight of nopalitos was 112 g and 106 g, respectively. We observed an insect attack (Dactylopiidae), and it was necessary to make two applications of a biological soap for pest control. The presence of this pest was almost exclusively in cv. Opuntia inermis, producing yellowish color in some cladodes.

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Xenia Wolff

Chayote (Sechium edule Swartz) is a minor vegetable crop gaining in popularity in the U.S., but with only scant cultural information on it available. The soil pH and water requirements-and the effects of various soil amendments on plant productivity were detemined in three separate greenhouse pot studies. Chayote plants were grown in either one of eight soil pH levels (5.0 to 6.5), were watered at one of three rates (1.3, 2.5, or 5.0 cm per week), or were planted in one of 16 soil amendment treatments (Oliver silt loam soil or a 1 soil: 1 peat moss (v/v) mix amended with inorganic N-P-K fertilizer, 25 or 50 kg cow or rabbit manure/ha, or 12.5 or 25 kg chicken manure/ha). Data on date of germination, plant height, single and total leaf areas, total plant and separate plant part fresh and dry weights, and presence of flowers were collected. Greatest plant productivity was achieved with a soil pH range of 5.6 to 6.5, a watering rate of 2.5 cm per week, and with several of the soil amendment treatments.