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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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Erin Alvarez, Sloane M. Scheiber, and David R. Sandrock

Water use is the most important environmental issue facing the horticulture industry. As a result, many water management districts are recommending native plants for their putative low-water requirements. Numerous textbooks and trade journals claim native plants use less water than non-natives; however, previous research found no difference in water use efficiency in the field between native and non-native species. Furthermore, recommendations of ornamental grasses for use as low-maintenance and low-water-requiring landscape plants have recently escalated. This study evaluated non-native Miscanthus sinensis `Adagio' and the native Eragrostis spectabilis for irrigation requirements and drought response in a landscape setting. To simulate maximum stress, both species were planted into field plots in an open-sided, clear polyethylene covered shelter. Each species was irrigated on alternating days at 0, 0.25, 0.5, or 0.75 L for a 90-day period. Growth index and height were recorded at biweekly intervals, and final shoot and root dry masses were taken at completion of the study. Significant treatment and species effects were found for height, growth index, shoot dry weight, and biomass. Plants receiving 0.75 L of irrigation had the greatest growth, and non-irrigated plants grew significantly less. Comparisons between species found growth was greatest among Eragrostis spectabilis plants for all parameters.

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C. M. Geraldson

The purpose of this study was to evaluate the commerical feasibility of a containerized gradient concept with relevance to water requirement, pollution potential, and production efficiency. Basic components included one-half cu ft of media/plant with 2 plants/rigid plastic container. Phosphorous, liming material and micronutrients were mixed in the media and the N-K was banded on the surface at both ends of the container which was protected by a plastic cover. Intermittent micro-irrigation was used to maintain either a lateral or vertical nutrient/moisture gradient. Variations in the media, the size and shape of the container, and the frequency and time of water applications were included in the evaluations. In the spring of 1991, 65 gallons of water was utilized to produce 22.9 lbs of marketable tomatoes/plant. Leaching was insignificant and the water required on an acre basis was projected as 4.8 acre inches with a 2000 plant population. The results indicate that the containerized gradient concept is potentially feasible as a sustainable production system.

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Enrique Troyo-Diguez and Federico Salinas-Zavala

A water demand model based on the plant–water–climate interactions is proposed to establish the effects of the photosynthetically active radiation (PAR) on the water demand processes of a crop. It is shown that a relationship exists between PAR, leaf temperature, and the transpiration of regional ecotypes of Northwest Mexico from Asia in the middle of the century. These ecotypes were found in the influence area of the Sierra de La Laguna, B.C.S., Biosphere Reserve. Estimated relationship was backed by measurements of leaf and ambient temperatures, and PAR, of which the transpiration is dependent. It is concluded that this procedure is useful to establish the expected level of transpiration of pigeonpeas and thus, their water requirements. The observed phenotype characteristics suggest the usefulness of pigeonpeas in intensive ecosystems; grain yield was near 6 Mg·ha–1. The results enable us to design appropriate horticultural systems in the villages of Sierra de La Laguna, which could include understorey horticultural species and pigeonpeas, a low-inputs crop.

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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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C. Catanzaro, S. Bhatti, and B.T. Jordan III

The U.S. Environmental Protection Agency limits the amount of nitrate and phosphate, yet these nutrients are applied in relatively large amounts during crop production. The objective of greenhouse studies conducted in 2002–05 was to determine the effects of calcined, attapulgite-type clays used as substrate amendments during production of containerized poinsettias, chrysanthemums, and ornamental grasses. Crops were grown with recommended rates of controlled-release fertilizers and irrigation volumes set to achieve a leaching fraction around 0.2. Results with poinsettias grown in substrates amended with clays were as follows: EC of leachate from poinsettia was reduced by up to 39% in the first few weeks after potting; orthophosphate concentration in leachate was reduced by up to 74% in peat-based substrate; cumulative irrigation volume required to produce plants in 16.5-cm containers was reduced by 11%. With two chrysanthemum cultivars, clays reduced EC of leachate and increased plant growth. A non-calcined clay reduced growth of poinsettia and `Oborozuki' Japanese sweetflag grass, but not `Karl Foerster' feather reed grass. Results from these studies suggest that, with controlled irrigation volumes, calcined clays added to a peat-based substrate can reduce leachate nutrient concentrations and reduce crop water requirements without negatively affecting crop growth or quality.

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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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Roberta J. Tolan and James E. Klett

Patmore green ash (Fraxinus pennsylvanica `Patmore'), Bur oak (Quercus macrocarpa), and Austrian pine (Pinus nigra), were used to measure growth differences of trees produced using three different production methods: balled and burlapped, plastic container, and fabric container (grow bag). Two irrigation frequencies were also established. A pressure chamber was used to measure the xylem water potential and to determine tree water requirements and irrigation scheduling. The balled and burlapped trees showed the least new growth of the three production methods across all three tree types. The production method showing the most new growth varied by genera. Plastic container ash trees grew considerably more than the fabric container ash; fabric container oak grew significantly more than plastic container oak; and there was no measurable difference between the new growth of the plastic container and fabric container pines. The fabric container transplants required more frequent irrigation than did the balled and burlapped trees. Under high temperature and drought conditions, fabric container trees showed stress earlier than did the balled and burlapped or plastic container trees.

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C.M. Geraldson

The gradient concept is designed with a soluble source of N–K banded on the soil bed surface in conjunction with a continuing source of water that synchronizes the nutrient–water input with rate of removal by the root. By placing the N–K on the surface rather than conventionally in the bed, nutrient movement to the root shifts from mass flow to diffusion. Nutrients that move by mass flow are a function of water requirement and potentially a source of nutritional instability. With the shift to movement by diffusion, nutrients move independently of the water to replace those removed from the gradient by the root. The gradient with a continuing nutritional stability replaces the variable and limited stability potential of the soil. Commercial tomato yields in Florida more than doubled with the shift to the gradient-mulch procedure. A containerized version of the concept (The EarthBox™) has been most successful for the home gardener and substantiates the validity of the gradient. Most innovative procedures with the gradient as the buffer component minimize pollution, require minimal management, and use minimal water with microirrigation or an enclosed system. To better understand the gradient concept and utilize the procedure, it may be necessary to consider the procedure as a nutritional paradigm shift.