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  • Author or Editor: Walker Williams x
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Experiments in two consecutive years indicated that barnyardgrass (Echirzochloa crusgalli L.), large crabgrass (Digitaria sanguinalis L.), and giant foxtail (Setaria faberi Herrm.) reduced growth of container-grown `San Jose' juniper (Juniperus chinensis L. `San Jose') 83 days after transplanting grass seedlings into the containers. Grass densities of one to six weeds per container reduced `San Jose' juniper growth. By 83 days of grass interference, juniper shoot dry weight was reduced as much as 43% by six weeds per container.

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A 3 × 2 factorial experiment was initiated in the fall of 1990 to study the interaction between evaporative cooling and hydrogen cyanamide on the budbreak, yield, and fruit maturation rate of Perlette grapevines grown in the Coachella Valley of California. Main plots consisted of evaporative cooling treatments [water applied continuously via overhead sprinklers for 0, 10, or 24 hours per day], and split plots consisted of hydrogen cyanamide applications [0 or 2% (v/v)]. Hydrogen cyanamide was more effective for the advancement of budbreak and fruit maturation than evaporative cooling in both 1991 and 1992. No additional advancement of budbreak and fruit maturation was observed when evaporative cooling and hydrogen cyanamide were combined compared to when hydrogen cyanamide was applied alone. Packable, unpackable, and cull yield per vine did not differ significantly among the treatments in 1991, while both evaporative cooling and hydrogen cyanamide reduced cluster number per vine and fruit yield in 1992.

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Various inorganic soil amendments have been promoted as a means of improving the chemical and physical properties of certain soils. To test this hypothesis, a marginally productive soil was supplemented with 20%, 40%, 60%, and 80% (v/v) of either selected inorganic amendments or sand. Amendments consisted of commercially available diatomaceous earth, calcined clay, zeolite, and crystalline SiO2. The soil material was extracted from the argillic horizon of a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). Ability of these soil-amendment mixtures to promote `Tifway' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] growth was evaluated under greenhouse conditions, and contrasted to that obtained in nonamended soil. Selected chemical and physical properties that are pertinent to plant growth were also evaluated. The experiment, which was conducted 3×, began with a §60-day period in which both water and nutrients were optimum. This was followed by a 30-day drought. During optimum water and nutrients, no soil-amendment treatment(s) consistently resulted in superior bermudagrass growth compared to soil alone. However, <2% of the bermudagrass tissue that was produced during the drought became green and succulent with the resumption of irrigation in nonamended soil. This percentage was exceeded by all treatments that contained either ≥60% diatomaceous earth (Axis), or ≥40% calcined clay (Profile); and by 100% zeolite (Clinolite) and 100% silica (Green's Choice). Drought-sustaining ability of soil-amendment mixtures was significantly (P < 0.05) correlated with water-holding ability, soil strength, bulk density, and oxygen diffusion rate, but not correlated with either pH or cation exchange capacity (CEC). While certain inorganic amendments did improve the drought-sustaining ability of soil, the amount required was generally ≥40%.

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A comparison was made among 16 native North American Vitis species and Vitis vinifera L. ('Carignane') grown in the San Joaquin Valley of California with or without irrigation over 2 years. Predawn water potential (ΨPD), predawn leaf osmotic potential (Ψπ), midday leaf (Ψl), and stem water potential (Ψstem), stomatal conductance (gs), net CO2 assimilation rate (A), and intrinsic water use efficiency (WUE) were measured on five dates during the growing season the first year of the study and pruning weights were evaluated both years. Net gas exchange and water potential components taken on the last measurement date in 1992 and pruning weights of the nonirrigated species were less (or more negative for Ψ components) than those of the irrigated vines. The 17 Vitis species were ranked according to their relative drought tolerance based upon their performance without irrigation and when compared to their irrigated cohort. The Vitis species considered most drought tolerant were V. californica, V. champinii, V. doaniana, V. longii, V. girdiana, and V. arizonica. Those six species generally had high values of A, gs, and pruning weights and more favorable vine water status at the end of the study than the other species when grown without irrigation. The drought-induced reductions in the measured parameters also were less for those species when compared to their irrigated cohorts. The least drought tolerant species were, V. berlandieri, V. cinerea, V. lincecumii, V. riparia, and V. solonis. The drought-tolerant rankings were generally associated with the species' native habitat and probable soil water availability.

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