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F.T. Davies Jr., J.N. Egilla, J.C. Miller Jr. and J.A. Saraiva Grossi

The influence of the mycorrhizal fungus Glomus intraradices and reduced levels of G. intraradices treated with the isoflavonoid formononetin was tested on growth and gas exchange of container-grown potato plants. Tissue culture-produced minitubers of Solanum tuberosum cv. Russet Norkotah and Russet Norkotah selection TX112 were subjected to four treatments: 1) G. intraradices at 750 propagules per container, 2) G. intraradices at 376 propagules per container, 3) G. intraradices at 376 propagules per container treated with the isoflavonoid formononetin, and 4) noncolonized plants. Plants were grown under glasshouse conditions in 1500-mL containers containing a sterilized sand: sandy loam soil, and fertilized with Long Ashton nutrient solution modified to supply phosphorus at 11 ug P/mL. The experiment was initiated on 4 May 1998 and terminated on 27 Aug. 1998, during which the plants were exposed to adverse high temperatures (mean high: 30.7 °C). Both cultivars responded similarly to mycorrhizal treatments. Formononetin enhanced growth of myocorrhizal plants and increased total colonization, arbuscule, and hyphae development. Only formononetin-treated mycorrhizal plants had increased shoot growth. Net photosynthesis and stomatal conductance were generally greatest with reduced levels of mycorrhiza and formononetin treated mycorrhizal plants.

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Patricia I. Garriz, Hugo L. Alvarez and Angel J. Alvarez

This investigation was undertaken to determine the response of pear fruit growth and quality to shade imposed during development. Whole branches of mature `Bartlett' trees on P. communis L. growing at the Experimental Farm on a sandy loam soil were covered with a 20% transmission black, neutral-density shadecloth from 43 days after full bloom (DFB) to 138 DFB, during the 1995–96 growing season. Two comparable branches on each of five uniform trees were selected for good exposure and one branch of each pair was shaded. Fruit diameters were measured at 2-weekly intervals. Pulp pressure and soluble solids concentration (SSC) were measured at harvest time on 31 Jan. Specific leaf mass (SLM) also was recorded (leaf dry mass was obtained by drying discs at 80°C). Relative fruit growth rates were initially similar between light regimes, becoming lower for the shaded fruit at the subsequent measurements. Light exposure induced a 8.76% increase in final fruit diameter (66.40 mm); this increment would appear to depend on carbohydrate availability, since highly significant differences at P ≤ 0.01 emerged in the spur SLM of the exposed and covered branches (7.68 vs. 5.79 mg·cm–2, respectively). SCC was similar for the two light environments, while flesh firmness was 8.80% higher in the shaded fruit. Our results indicate that solar radiation deprival had clearly detrimental effects on fruit growth and maturity, and they provide a basis for improving pruning and training practices in the future.

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L. Aguilera, F.T. Davies Jr, V. Olalde-Portugal, S.A. Duray and L. Phavaphutanon

Seedlings of Capsicum annuum L. cv. San Luis were grown in pots containing a pasteurized mixture of sand and sandy loam soil inoculated or noninoculated with the V-A mycorrhizal (VAM) fungus Glomus intraradices Schenck et Smith. Long Ashton nutrient solution (LANS) was modified to supply P at 0, 11 or 44 μg·ml–1. Diurnal gas exchange measurements were taken 15, 30 and 50 days after the experiment was initiated. Plant growth, leaf elemental content, and mycorrhizal development were assessed 52 days after transplanting. Gas exchange and net photosynthesis were enhanced by mycorrhiza and full strength LANS fertilization (44 μg·ml–1). The symbiosis increased leaf nutrient content of P, K, Mg, S, Fe, Mn, Zn, Cu, B, Mo, and Al. Mycorrhizal plants had higher shoot dry weights, leaf number, leaf area, and fruit primordia than nonmycorrhizal plants with P at 0 and 11 μg·ml–1. Root colonization (arbuscules, vesicles, and internal and extraradical hyphae development) were higher with P at 0 and 11 μg·ml–1. The quantity of spores recovered in soil was independent of P treatments.

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D.T. Drost, J.W. Macadam, L.M. Dudley and N. Soltani

Groundwater, contaminated with sulfur (S) at concentrations higher than allowable for drinking water, may be suitable for irrigation. Our objectives were to determine the growth response and mineral uptake of two vegetables grown in high-S irrigation water. Bean (Phaseolus vulgaris) and broccoli (Brassica oleracea L.), grown in 8-L pots containing a calcareous sandy loam, were irrigated with waters containing from 58 to 582 mg S/L. Plants were harvested and growth was measured at 4, 8, or 12 weeks. Soil paste extracts and dry plant tissue were analyzed by inductively coupled plasma (ICP) spectroscopy at each harvest. Bean shoots and pod dry weight decreased by 32% and 28%, respectively, as S concentration increased. Although final pod number was not affected by the irrigation treatments, pod yields (4 weeks) decreased as S concentration increased. Broccoli growth was not affected by increasing S concentration at any of the harvest dates, though head diameter did decrease as S increased. Magnesium, sodium, and sulfur accumulated in shoot tissue (leaves and stems) of both species in proportion to their concentration in the irrigation water. It appears that high-S waters can be used to grow these vegetables without negative effects on growth.

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Regina P. Bracy and Richard L. Parish

Improved stand establishment of direct-seeded crops has usually involved seed treatment and/or seed covers. Planters have been evaluated for seed/plant spacing uniformity, singulation, furrow openers, and presswheel design; however, effects of presswheels and seed coverers on plant establishment have not been widely investigated. Five experiments were conducted in a fine sandy loam soil to determine effect of presswheels and seed coverers on emergence of direct-seeded cabbage and mustard. Seed were planted with Stanhay 870 seeder equipped with one of four presswheels and seed coverers. Presswheels included smooth, mesh, concave split, and flat split types. Seed coverers included standard drag, light drag, paired knives, and no coverer. Soil moisture at planting ranged from 8% to 19% in the top 5 cm of bed. Differences in plant counts taken 2 weeks after planting were minimal with any presswheel or seed coverer. Visual observation indicated the seed furrow was more completely closed with the knife coverer in high soil moisture conditions. All tests received at least 14 mm of precipitation within 6 days from planting, which may account for lack of differences in plant emergence.

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D.R. Earhart, M.L. Baker and V.A. Haby

Phosphorus (P) concentration in surface waters from non-point agricultural sources is an increasing resource management concern. This study was conducted at Overton, Texas, on a Bowie fine sandy loam (fine-loamy, siliceous, thermic, Plinthic Paleudults) to evaluate cool-season legumes for P uptake following poultry litter (PL) application rates on spring vegetables. Treatments were PL rate (0, 1X, 2X, 4X) and a commercial blend (CB) for comparison. Cool-season legumes, consisting of crimson clover, berseem clover, hairy vetch, and red clover, were the subplots. The vegetable crop in Spring 1995 was watermelon. The 1X PL rate was 2.2 t·ha-1 and the CB was 44.8N-0P-32.5K kg·ha-1. Dry matter yield was decreased by the 4X PL rate. Plant P concentration increased linearly as PL rate was increased. The greatest P uptake (4.1 kg·ha-1) was at the 2X rate. Hairy vetch had the greatest yield (1,875 kg·ha-1), plant P concentration (0.53%), and P uptake (9.6 kg·ha-1). PL rate increased soil P concentration at all depths. The least amount of P accumulation was from CB and was equal to the control. Hairy vetch appears to have the capability of removing a greater amount of P and reducing soil concentration when compared to the other legume species tested.

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D. J. Makus

Four cassava (Manihot esculenta Crantz) accessions were received from the USDA, ARS Plant Introduction Station in Mayaguez, PR on 16 Jan. 1996. The next day the 15- to 20-cm-long cuttings were propagated individually in 1-gal. pots containing Metro Mix No. 4 for 10 weeks before field setting into a transition Hidalgo-McAllen fine sandy loam soil on a USDA, APHIS site near McCook, Texas. Three plant establishment methods, control (no soil amendment), addition of 15 Mt bagasse/ha, or 50 kg cross-linked polyacrylamide/ha into the planting trench were evaluated. The 2 × 1.2 m spacings on 15-cm-high beds provided 4036 plants/ha. Plants received a total of 35.8 cm of water between field planting and harvest (230 days). Mid- and late-season soil moisture (kg/m3) at 38 cm depth only was lowest in soil containing bagasse. Establishment method had little or no effect on plant size, leaf nutrients, leaf pigment concentrations, root dry matter, or root yield. Accessions differed in many of these attributes except root yield, the means of which ranged from 5 to 9 Mt/ha. Only roots survived an air temperature of -5.4 °C on 19 Dec.

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Gerry H. Neilsen, Denise Neilsen, Peter Parchomchuk and Eugene Hogue

Soil solution monitoring has been suggested as an appropriate procedure to optimize fertigation timing and application rate. Soil solution NO3-N concentrations were measured for two growing seasons on a sandy loam soil when 5, 20 or 30 g N per season per tree were fertigated daily to apples as calcium nitrate from mid May-mid July. Soil solution NO3-N concentrations at 30 cm depth changed rapidly in response to both the initiation and cessation of fertigation, with values ranging from 10-20 ppm, 60-100 ppm and 100-200 ppm for the low to high treatments respectively. The rapid response to NO,-fertilizers implied a potential to control closely the timing of N fertilizer applications. In another experiment, `Empire' apple trees were fertigated 5 times/week from May 31 to August 9 with 30 g N/tree applied either as ammonium sulphate or as calcium nitrate. With calcium nitrate as the N source, NO3-N rapidly increased when fertigation was initiated and fell when fertigation ended. In contrast, with ammonium sulphate, NO3-N was low for about 30 days after initiation of fertigation, then increased to 100 ppm and remained elevated for 40-50 days after fertigation ended. The potential control of N nutrition appeared to be less exact when fertigating NH4-N.

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William C. Olien, C.P. Hegwood Jr and James M. Spiers

Muscadine (Vitis rotundifolia Michx.) vineyards can be difficult to establish due to poor vine growth or survival during the first year after planting. Effects of the planting hole (five types), root manipulation (three levels), and peat amendment (0% and 50%) on first-year growth were studied at two sites with different soil types: a sandy loam (well-drained) and a silty loam (moderately well-drained). The planting hole had the major effect at both sites; large holes (25 liters) shoveled with straight or angled sides resulted in more shoot and root dry weight and greater total root length than auger holes (21 liters) or small shovel holes (10 liters). Vine response to planting in a subsoil slot 0.5 m deep × 6 m long was similar to that in large holes in sandy soil and small holes in heavier soil. Root manipulation treatments had little effect on vine establishment. Root pruning at planting, with or without root separation, did not increase vine dry weight relative to an undisturbed root ball in either soil type, but total root length was increased by root pruning in the heavier silty loam soil. Peat amendment increased total root length in the sandy soil but not in the silty loam soil.

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Bharat P. Singh and Wayne F. Whitehead

In literature, amaranth is described as a stress tolerant crop. However, most of the investigations have been concerned with the production of grain crop. The soil moisture regime which promotes maximum vegetative growth is yet to be established. During 1993, the vegetative growth response of amaranth to different soil moisture levels was determined in a greenhouse study. Amaranth cultivar Hin Choy was grown in Dothan sandy loam soil at four soil moisture levels of 6.0, 9.0, 12.0 and 14.0% (w/w) in a randomized complete block experiment with ten replications. Plant height, leaf number, leaf area, leaf fresh and dry weight, stem fresh and dry weight, root fresh and dry weight, leaf-stem ratio, and stem fresh and dry weight were recorded. All parameters gained significantly with each increment in the soil moisture level up to 12%. There was no difference in plant response between 12% and 14% soil moisture. The study indicated that for optimum vegetative growth, amaranth requires a moisture stress free soil environment.