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R. Seth Peterson* and Daniel Drost

Asparagus producers have reported a decrease in plant longevity and plant productivity in asparagus fields. Irrigation methods and amounts and early harvest pressure are thought to be some factors affecting asparagus longevity and productivity. The objectives of this study were to determine how irrigation method (sprinkler/drip), amount (0, 75, 150% ET), and harvest pressure (yes/no) modify asparagus growth in the year after planting. In April 2002, plots were planted with as-paragus cultivar Jersey Giant. All plots were treated the same during the establishment year. Each plot was 6.1 m long by 2 rows wide. All plots were separated by a guard row. There were 5 replications. Each irrigation method and amount was divided into two harvest treatments. One row was harvested for three weeks in 2003 (952 kg/ha) while the other was not harvested. Irrigation treatments began after harvest. In 2003, 100% ET from 10 June 10 to 14 Sept. was 55 cm. After correcting for precipitation and crop coefficient, the 75% ET treatment received a total of 28 cm of water while the 150% treatments received 47 cm. There was no difference in fern fresh weight between 150% and 75% ET for the drip irrigates asparagus, but both were significantly greater than non-irrigated treatment. In contrast, fern fresh weight decreased linearly as irrigation amounts decreased in the sprinkler treatments. Yield differences are not expected between drip and sprinkler in 2004. Yield reductions are expected relative to irrigation amounts.

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Daniel Drost and Darlene Wilcox-Lee

Asparagus is considered a relatively drought tolerant plant, but few studies are available on the gas exchange response to soil moisture stress. Seedlings were grown in the greenhouse for six months before initiation of the water stress treatments. Soils were allowed to dry to matric potentials of -0.05, -0.3 and -0.5 MPa before rewatering to pot capacity. Gas exchange and fern water potentials were measured diurnally on asparagus plants when soil matric potentials reached their minima. Decreasing soil matric potentials decreased net carbon dioxide assimilation, stomatal conductance and fern water potential. Assimilation rates (6 am) were between 3 and 5 umols m-2 s-1 for all soil moisture treatments. Carbon assimilation rates of 10, 8, and 7 umols m-2 s-1 were recorded at 10 am for the -0.05, -0.3 and -0.5 MPa soil matric potentials, respectively. Assimilation rates decreased sharply over the remainder of the day. The diurnal pattern for conductance were similar to the assimilation rates. Fern water potentials were greater in the -0.05 MPa than in the -0.5 MPa treatment for all measurement periods with an intermediate response for soil matric potentials of -0.3 MPa. Fern water potentials were highest at 6 am (-0.2 to -0.6 MPa) before declining to their minima (-1.5 to -1.8 MPa) at 10 am. Water potentials remained at these low levels throughout the day before recovering slightly at 6 pm.

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Daniel Drost and Darlene Wilcox-Lee

Asparagus is considered a relatively drought tolerant plant, but few studies are available on the gas exchange response to soil moisture stress. Seedlings were grown in the greenhouse for six months before initiation of the water stress treatments. Soils were allowed to dry to matric potentials of -0.05, -0.3 and -0.5 MPa before rewatering to pot capacity. Gas exchange and fern water potentials were measured diurnally on asparagus plants when soil matric potentials reached their minima. Decreasing soil matric potentials decreased net carbon dioxide assimilation, stomatal conductance and fern water potential. Assimilation rates (6 am) were between 3 and 5 umols m-2 s-1 for all soil moisture treatments. Carbon assimilation rates of 10, 8, and 7 umols m-2 s-1 were recorded at 10 am for the -0.05, -0.3 and -0.5 MPa soil matric potentials, respectively. Assimilation rates decreased sharply over the remainder of the day. The diurnal pattern for conductance were similar to the assimilation rates. Fern water potentials were greater in the -0.05 MPa than in the -0.5 MPa treatment for all measurement periods with an intermediate response for soil matric potentials of -0.3 MPa. Fern water potentials were highest at 6 am (-0.2 to -0.6 MPa) before declining to their minima (-1.5 to -1.8 MPa) at 10 am. Water potentials remained at these low levels throughout the day before recovering slightly at 6 pm.

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R. Seth Peterson* and Daniel Drost

Asparagus producers have reported a decrease in plant longevity and plant productivity in asparagus fields. Eleven commercial sites (6 in California and 5 in Washington) were monitored starting in Spring 2003. The purpose in monitoring was to evaluate how long-term growth dynamics are affected by harvest pressure. Sites were planted as crowns in Spring 2002 and farm irrigation methods included furrow, sprinkler, and drip. Most sites were harvested starting in Spring 2003 at varying pressures. Harvest yields ranged from 0 to 1300 kg·ha-1. Carbohydrate (CHO) levels in the roots were sampled over the entire growing season and assessed with AspireUS (www.aspireus.com). At the last sampling in Oct. and Nov. 2003, CHO levels ranged from 438 mg·g-1 to 712 mg·g-1 (97% to 158% of the ideal). This resulted in a root CHO load of 2.6 to 6.3 megagrams/hectare. Root mass and distribution was sampled in Spring 2003 and again at the end of the growing season. Root biomass increased by 18% to 487% of the previous year's growth. Fern number, fern mass and plant population were also sampled. Fern number ranged from 3.2 to 6.4 stems per plant and total fern weight ranged from 8.9 to 36.2 megagrams/hectare. Plant populations were reduced by 3% to 19% when compared to the initial planted population. Findings suggest that excessive harvest pressure in the year after planting adversely affects storage CHO accumulation and root growth. Additional site monitoring will occur through 2005.

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Darlene Wilcox-Lee and Daniel T. Drost

Crowns and tranplants of `Martha Washington' (MW) and `Jersey Prince' (JP) asparagus were planted in 1985. Plots were harvested for 0,2,4 weeks (traditional schedule); 1,2,6 weeks (moderate harvest pressure); or 2,4,8 weeks (severe harvest pressure) in 1986, 1987, and 1988, respectively. All plots were harvested for 8 weeks after 1988. An AOV was performed to test the main effects of cv, planting technique and harvest schedules and interactions on early and total season yield of large, medium-sized and total spears. MW produced a significantly higher yield of both early and total season large spears than JP in all years. Total yields did not differ between cvs. There was no significant effect of planting technique on yield in any year. Harvest schedules imposed in the first 3 years had significant long term effects on yield. Although severe harvest pressure produced larger yields than the other schedules in 1986-1988, from 1989-1991 yields were lowest in the severe harvest pressure plots. The traditional harvest schedule produced similar yields to the moderate pressure schedule. There were no consistent interactions between cultivar, planting technique and harvest schedule These data indicate that a slightly more aggressive harvest schedule in the early years of an asparagus planting would not have long term deterimental effect on yield. However, severe cutting pressure can reduce yields compared to traditional cutting schedules for at least 3 years after initial harvest pressure treatment

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Daniel Drost, Darlene Wilcox-Lee, and Richard Zobel

Published data on the spatial patterns and periodicity of root growth in asparagus are limited. During the 1989 growing season growth and distribution of both fleshy and fibrous roots were monitored in a 7 year old asparagus planting. Soil cores were removed at 15 cm intervals to a depth of 90 cm at 40 and 80 cm from the plants in asparagus beds which had been maintained under conventional (CT) and no-till (NT) production systems. Fleshy and fine roots were separated from the soil and root length densities calculated. Harvests began in late March and continued at three week intervals until early November. Fine root growth was greater in the NT than CT in all depths and at both locations in March. Greatest lengths of fine roots were at the 15-60 cm depths for both CT and NT. This pattern was consistent throughout the season. Fine root lengths decreased by one half by the middle of the year (July) and remained at those levels until the last harvest (Nov). Fleshy root lengths were more variable, however NT generally had greater lengths than CT. Greatest length of fleshy roots were located in the 15-60 cm depths for both CT and NT treatments. Few fleshy roots were found below the 60 cm depth.

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Darlene Wilcox-Lee and Daniel T. Drost

Seedlings of the asparagus cvs Mary Washington (MW) and Syn 4-56 (4-56) were grown at minimum soil matric potentials (SMP) of -0.05, -0.10, and -0.30, -0.50 or -1.5 MPa. Decreases in shoot dry weight leaf area, storage and fibrous root dry weights, and total root and plant dry weight were an exponential function of soil moisture in both cvs. Most of the growth inhibition occurred between the -0.05 and the -0.30 MPa levels of soil moisture, with little further response to SMP drier than -0.30 MPa. Consistent differences between the two cvs, regardless of SMP were apparent in leaf area, shoot dry weight, storage and fibrous root dry weights and root/shoot ratios. MW produced greater leaf area and shoot dry weights than did 4-56 at high SMP and exhibited greater inhibition of shoot dry weight by low SMP than did 4-56. Conversely, 4-56 produced greater storage root dry weight than MW at all SMP., although in mature field-grown plants, 4-56 produced greater fern weight, crown weight and number and stem numbers than MW. Root/shoot ratios generally increased with decreasing SMP. However, the root/shoot ratio of 4-56 was greater than that of MW over the entire range of soil moisture and increased more with decreasing SMP than did MW. Stomatal conductance (gs), fern xylem potential (), and net C02 assimilation rates decreased with decreasing SMP in a similar manner in both cvs. were

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Daniel Drost, Gilbert Long, and Kimberlee Hales

Without a clear understanding of individual farms and farming practice, progression toward more sustainable vegetable production cannot occur. Seventy randomly selected vegetable farmers in Utah were surveyed by telephone and mail to gather baseline data on their agricultural practices. The Utah vegetable farmers profile generated by this survey included a measure of each respondent's attitude toward sustainable agricultural practices and his or her interest in further cooperation with research and extension. A farming index to measure practices used and a perceptual index measuring farmer's views regarding sustainable practices were developed, pilot tested, and refined during the project. Although the perceptual index did not serve as a proxy for actual farm practice, it identified farmers who had an appreciation for sustainable agriculture. Together with the farming index, we now have detailed information on actual farm practices for a variety of different vegetable farmer groups. The use of these two indices will help measure the effectiveness of future research and extension efforts as farmers progress toward more sustainable vegetable production.

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Darlene Wilcox-Lee and Daniel T. Drost

Asparagus officinalis L. cv. Centennial established with transplants in 1983 was maintained with tillage or a no-till (NT) system to evaluate effects of tillage on yield and plant growth in a mature asparagus planting. Metribuzin or metribuzin + napropamide at 1.12 and 1.68 kg a.i./ha, respectively, were used for weed control in both tillage regimes. Marketable yields were assessed for 5 years. In 1989, in addition to yield data, destructive harvests of entire plants were made every 3 weeks from March to November to evaluate the effect of tillage on fern, crown, and bud growth, and carbohydrate status. Yields were reduced by tillage from 12% to 50% from 1985 to 1989. There were no herbicide effects nor was there an effect on yield due to an interaction between herbicides and tillage. All indices of growth measured for NT exceeded those in tilled plots, although seasonal patterns of growth were similar in both. Crown and fern weight, bud cluster, and bud and fern counts were higher by 178%, 175%, 152%, 161%, and 195%, respectively, in NT than in tilled plots. The metribuzin + napropamide combination did not reduce fern fresh weight or yield, but significantly reduced the number of bud clusters, buds, and ferns when compared to metribuzin alone. Chemical names used: 4-amino-(1,1-dimethylethyl)-3-(methylthio)-l (metribuzin); 2,4-triazin-5(4H) -one, N,N-diethyl-2-(naphthalenyloxy)-propanamide (napropamide).

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Nathan C. Phillips, Steve R. Larson, and Daniel T. Drost

The genus Allium is distributed worldwide and includes about 80 North American species, with at least 13 occurring in Utah. Our study focuses on the population dynamics of three Allium species native to Utah; Allium acuminatum, A. brandegei, and A. passeyi. In conjunction with our studies of life history, growth characteristics, demographics, and habitat, we are interested in determining the levels of genetic variation in these species. This study examines amplified fragment length polymorphism (AFLP) within and among five Allium acuminatum, four A. brandegei, and three A. passeyi populations native to Utah. These species have contrasting abundance and distribution. The study populations were selected along an elevation gradient to represent within-species habitat differences. About 10–20 plants from each of the 12 populations were genotyped using six AFLP primer combinations, which detect DNA variation within and among all three species. These data will be used to compare levels of genetic variation and isolation among populations and species.