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D.G. Levitt, J.R. Simpson, and J.L. Tipton

Although water conservation programs in the arid southwestern United States have prompted prudent landscaping practices such as planting low water use trees, there is little data on the actual water use of most species. The purpose of this study was to determine the actual water use of two common landscape tree species in Tucson, Ariz., and water use coefficients for two tree species based on the crop coefficient concept. Water use of oak (Quercus virginiana `Heritage') and mesquite (Prosopis alba `Colorado') trees in containers was measured from July to October 1991 using a precision balance. Water-use coefficients for each tree species were calculated as the ratio of measured water use per total leaf area or per projected canopy area to reference evapotranspiration obtained from a modified FAO Penman equation. After accounting for tree growth, water-use coefficients on a total leaf area basis were 0.5 and 1.0 for oak and mesquite, respectively, and on a projected canopy area basis were 1.4 and 1.6 for oaks and mesquites, respectively. These coefficients indicate that mesquites (normally considered xeric trees) use more water than oaks (normally considered mesic trees) under nonlimiting conditions.

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Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema, and Dawn VanLeeuwen

Successful commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] production relies on mitigation of alternate bearing, which is a function of pistillate flower production. Mechanisms of floral initiation in pecan are not well understood. Our objective was to assess the impact of select plant growth regulators (PGRs) on return bloom for commercial application in pecan trees grown in the Southwestern United States. A 2-year study evaluated effects of ethephon, aminoethoxyvinylglycine (AVG), and gibberellin GA3 (GA3) on subsequent season return bloom in fruiting and nonfruiting pecan shoots. Cultivars used were mature Western and immature Western and Pawnee. Effects of PGRs on return bloom of nonfruiting shoots were different from fruiting shoots. As compared with untreated control, a GA3 treatment on fruiting shoots of mature ‘Western’ trees increased the number of flowers per new shoot by 125%. For nonfruiting shoots on the mature ‘Western’ trees, the number of flowers per new shoot decreased significantly by all PGR treatments and as much as 93% for AVG. In previously nonfruiting shoots on the immature ‘Western’ trees, a GA3 treatment reduced the number of flowers per new shoot in the next season by 88.2%. Results from immature ‘Pawnee’ shoots did not show statistically significant differences. The effects of these PGRs on subsequent season flowering in pecan are complex. This study suggests that PGRs can be used to increase or decrease cropload through effects on return bloom and therefore have potential uses for mitigating alternate bearing.

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Pedro Revilla and W.F. Tracy

Sweet corn is one of the most important vegetable crops in the United States, however the morphology and phylogeny of open-pollinated sweet corn cultivars has not been studied. Fifty eight open-pollinated sweet corn cultivars were characterized with thirty-four descriptors to provide information for breeders interested in broadening the genetic base of sweet corn. Principal component analysis and cluster analysis were performed to classify sweet corn cultivars based on morphology. Also, relationships among morphological variables in this set of cultivars were determined. The general ordination of cultivars followed an axis representing earliness, and plant, leaf, and tassel size, while ear and kernel attributes were less variable. The morphological variability among all of the widely used sweet corn cultivars, except `Country Gentleman', was not greater than the variability found among the `Golden Bantam' strains. Based on morphology, 52 of the cultivars could be considered as one race, which we propose be called `Northeastern Sweets'. These may be a subset of the race `Northern Flint'. Five of the remaining cultivars are from the north-central or southwestern United States and may represent races from those areas. The sixth cultivar is `Country Gentleman', a commercially important sweet corn cultivar. Due to the importance of `Country Gentleman' and the introgression of nonsweet germplasm into modern sweet corn, we believe that sweet corn should be defined based on its use as a vegetable and on the presence of one or more genes that increase sugar levels in the endosperm.

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Chris A. Martin and Jean C. Stutz

A distance learning course called Southwest Home Horticulture was developed and implemented at Arizona State University using video and Internet technologies to give nonhorticulture students an overview of urban horticulture in the southwestern United States. Fourteen, one-half-hour video programs about topics in southwestern residential landscaping, plants materials and landscape best-management practices were produced in ≈800 working hours. The video programs are now telecast weekly, each academic semester, on the regional public television station and the educational channel of several cable television systems. We found that students who enrolled in the course were most likely to tape the programs on a video cassette recorder and watch them at their own convenience, one to three times. A World Wide Web (Web) site on the Internet was developed as a supplement to the video programs. The Web site was organized into a modular format giving students quick access to auxiliary course-related information and helpful resources. When asked, ≈90% of the students indicated that the Web site was a helpful supplement to the video programs. Use of video and Internet technologies in tandem has enabled nonhorticulture major students to learn about home horticulture in an asynchronous or location and time independent fashion.

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Esmaeil Fallahi, Zahra Mousavi, and D. Ross Rodney

The influence, of 10 rootstocks on growth, yield, and fruit quality of `Orlando' tangelo (Citrus paradisi Macf. × C. reticulata Blanco) was studied for 7 years under the arid climate of southwestern Arizona. Trees on macrophylla (Alemow) (C. macrophylla Wester) were the most precocious and produced the highest yields 4 years after planting. Seven-year cumulative yields of trees on Carrizo citrange [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.], Yuma citrange (P. trifoliata × C. sinensis), Volkamer lemon (C. limon Burm f.), rough lemon (C. jambhiri Lush), Taiwanica (C. taiwanica), and macrophylla were similar and higher than those on Savage citrange (P. trifofiata × C. sinensis), Batangas mandarin (C. reticulata Blanco), Ichang pummelo (C. ichangensis hyb.), and Palestine sweet lime (C. limettoides Tan.). Trees on Carrizo citrange had relatively large tree canopies and larger fruit, and fruit from trees on Volkamer lemon and rough lemon was lower in total soluble solids concentration (TSS) and total acids (TA) than fruit from trees on other rootstocks. Fruit from trees on Savage citrange was smallest but had the highest TSS. Considering yield, growth, and/or various quality factors, Volkamer lemon, rough lemon, Yuma citrange, and particularly Carrizo citrange, are suitable for `Orlando' tangelo in the arid regions of the southwestern United States. Trees on macrophylla, Savage citrange, and Ichang pummelo had small canopies and were least productive. `Orlando' tangelo trees on Savage citrange and Ichang pummelo rootstocks, however, might be good choices at a spacing closer than 7 × 7 m because of their high fruit TSS and fruit size, respectively. Trees on Palestine sweet lime declined and had low yields, and those on Batangas mandarin had low yields and poor fruit quality. These rootstocks are not recommended for `Orlando' tangelo under conditions similar to those of this experiment.

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Jeffery C. Kallestad, Theodore W. Sammis, John G. Mexal, and John White

Optimal pecan (Carya illinoiensis) production in the southwestern United States requires 1.9 to 2.5 m of irrigation per year depending on soil type. For many growers, scheduling flood irrigation is an inexact science. However, with more growers using computers in their businesses, and with soil moisture sensors and computerized data-collection devices becoming more inexpensive and accessible, there is potential to improve irrigation and water use efficiencies. In this project two low-cost soil monitoring instruments were introduced to a group of pecan producers. They were also given instruction on the use of Internet-based irrigation scheduling resources, and assistance in utilizing all of these tools to improve their irrigation scheduling and possibly yield. The objectives were to determine whether the technology would be adopted by the growers and to assess the performance of the sensors at the end of the season. Three out of the five growers in the project indicated they used either the granular matrix (GM) sensors or tensiometer to schedule irrigations, but compared to the climate-based irrigation scheduling model, all growers tended to irrigate later than the model's recommendation. Graphical analysis of time-series soil moisture content measured with the GM sensors showed a decrease in the rate of soil moisture extraction coincident with the model's recommended irrigation dates. These inflection points indicated the depletion of readily available soil moisture in the root zone. The findings support the accuracy of the climate-based model, and suggest that the model may be used to calibrate the sensors. Four of the five growers expressed interest in continued use of the tensiometer, but only one expressed a desire to use the GM sensor in the future. None of the participants expressed interest in using the climate-based irrigation scheduling model.

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Genhua Niu, Denise S. Rodriguez, Lizzie Aguiniga, and Wayne Mackay

Use of recycled water to irrigate urban landscapes and nursery plants may be inevitable as fresh water supplies diminish and populations continue to grow in the arid and semiarid southwestern United States. Lupinus havardii Wats. (Big Bend bluebonnet) has potential as a cut flower and Lupinus texensis Hook. (Texas bluebonnet) as a bedding plant, but little information is available on salt tolerance of these species. A greenhouse study was conducted to characterize the growth in response to various salinity levels. Plants were grown in 10-L containers and drip-irrigated with synthesized saline solutions at electrical conductivity levels of 1.6, 3.7, 5.7, 7.6, or 9.4 dS·m−1. Although shoot growth of L. texensis was reduced as salinity levels increased, it was visually acceptable (without any visual injury) when irrigated with salinity levels of less than 7.6 dS·m−1. All plants survived at 7.6 dS·m−1, whereas only 15% did at 9.4 dS·m−1. In contrast, L. havardii had leaf injury at 5.7 dS·m−1. No plants survived at 9.4 dS·m−1, and only 7% plants survived at 7.6 dS·m−1. In addition, growth of L. havardii was significantly reduced and plants were shorter at elevated salinity levels. Cut raceme yield of L. havardii decreased at salinity levels greater than 3.7 dS·m−1. However, no difference in cut raceme yield was observed between the control and 3.7 dS·m−1, although shoot growth was reduced. Overall, L. texensis was more salt-tolerant than L. havardii.

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Michael Maurer* and Justin Weeaks

Throughout much of the Southwestern United States, poor quality water and limited water resources require innovative methods to conserve water. No research to date has indicated whether seeded bermudagrass Cynodon dactylon can be established by using subsurface drip irrigation (SDI). In 2001 (Expt. I) and 2002 (Expt. II), seeded bermudagrass was evaluated for establishment using SDI. Treatments consisted of emitters and tubing spaced at 30, 46, and 61 cm. The control treatment consisted of pop-up sprinklers. Salinity accumulation is a concern when irrigating turfgrass in areas of poor water quality and low annual rainfall. Salinity accumulation was visible at the soil surface during establishment in 2001, but turfgrass showed no visible signs of stress due to salinity. In 2002, substantial rainfall reduced salinity accumulation during establishment as salinity was not present on the soil surface. Salinity accumulation was greater in most months at the 0-15 cm depth in both years compared to the 15-30 cm depth. Full turfgrass coverage (≥90%) for the control plots in 2001 was about 8.5 weeks and the SDI treatments had complete coverage in 10 weeks. Turfgrass coverage for all treatments in 2002 was 9 weeks. Expt. II had a slightly faster establishment rate due to greater rainfall and different soil characteristics than that of Expt. I. Root count and depth of roots for both years showed roots to 61 cm depth in all treatments. A general trend of higher salinity accumulation at the midpoint between tubing was seen in Expts. I and II. However, after significant rainfall salinity levels returned to concentrations comparable to initial soil salinity concentrations in both years. This research documents the ability to successfully establish seeded bermudagrass using SDI.

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A. Ruiz*, D.S. Rodriguez, G.A. Picchioni, J.G. Mexal, and T.W. Sammis

Low-cost, sustainable wastewater treatment systems are needed for rapidly-growing communities of the southwestern United States. The objective of this study is to develop a practical management plan for land application of industrial wastewater on native Chihuahuan Desert vegetation. To assess environmental impact and create the management plan, wastewater effluent characteristics, soil physicochemical changes, and mineral uptake of the vegetation were monitored. The effluent was saline, ranging from 2500 to 6000 mg·L-1 of TDS and dominated by Na and Cl. Total N ranged from 10 to 40 mg·L-1. Soils sampled in Dec. 2002 (after 11 months and 64 cm of effluent irrigation) increased in salinity in the top 60 cm from 1.85 to 3.5 dS·m-1, and SAR in the top 30 cm was close to 15, but diminished with depth. Branch samples of the co-dominant perennial shrub vegetation members (Larrea tridentata and Prosopis glandulosa) harvested in July 2002 had elevated Na and Cl concentrations (0.4% to 2.1% of dry weight, respectively). By Oct. 2002, L. tridentata leaves contained comparable Na and Cl concentrations as those of P. glandulosa, yet removed 2 to three times more Na, Cl, and total N per branch, while maintaining their dry mass per branch. This raises the possibility of interspecific variation among the shrub species in salinity stress tolerance and capacity to remove wastewater contaminants. These data will aid in determining total vegetation removal of effluent components, preventing adverse environmental impact to the site, and developing a practical management plan suitable for small communities seeking cost-effective wastewater handling protocols.

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Steven J. Guldan, Charles A. Martin, Jose Cueto-Wong, and Robert L. Steiner

Three legumes [hairy vetch (Vicia villosa Roth.), barrel medic (Medicago truncatula Gaerth.), and black lentil (Lens culinaris Medik.)] were interseeded into `New Mexico 6-4' chile pepper (Capsicum annuum L.) when plants were 20–30 cm tall (3 Aug., “early” interseeding) or when plants were 30–40 cm tall (16–17 Aug., “late” interseeding) in 1993 and 1994. Our objectives were to determine the effect of legume interseeding on cumulative chile yield, and late-season dry-matter and nitrogen yields of aboveground portions of the legumes. Legumes were harvested on 8 Nov. 1993 and 15 Nov. 1994. Chile yield was not significantly affected by legume interseeding. In 1993, legumes accumulated 57% more dry matter and 55% more N when interseeded 3 Aug. vs. 16 Aug. In 1994, legumes accumulated 91% more dry matter and 86% more N when interseeded 3 Aug. vs. 17 Aug. Aboveground dry-matter yields in 1993 ranged from 1350 kg·ha–1 for black lentil interseeded late to 3370 kg·ha–1 for hairy vetch interseeded early. Nitrogen yields ranged from 52 kg·ha–1 for black lentil interseeded late to 136 kg·ha–1 for hairy vetch interseeded early. In 1994, hairy vetch was the highest yielding legume with dry matter at 1810 kg·ha–1 and N at 56 kg·ha–1 interseeded early, while black lentil yielded the lowest with dry matter at 504 kg·ha–1 and N at 17 kg·ha–1 interseeded late. In the spring following each interseeding year, we observed that hairy vetch had overwintered well, whereas barrel medic and black lentil had not, except when a few plants of barrel medic survived the winter of 1994–95. Results from this study indicate that legumes can be successfully interseeded into chile in the high-desert region of the southwestern United States without a significant decrease in chile yield.