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A fundamental way to schedule irrigation is through the monitoring and management of soil water tension (SWT). Soil water tension is the force necessary for plant roots to extract water from the soil. With the invention of tensiometers, SWT measurements have been used to schedule irrigation. There are different types of field instruments used to measure SWT, either directly or indirectly. Precise irrigation scheduling by SWT criteria is a powerful method to optimize plant performance. Specific SWT criteria for irrigation scheduling have been developed to optimize the production and quality of vegetable crops, field crops, trees, shrubs, and nursery crops. This review discusses known SWT criteria for irrigation scheduling that vary from 2 to 800 kPa depending on the crop species, plant product to be optimized, environmental conditions, and irrigation system. By using the ideal SWT and adjusting irrigation duration and amount, it is possible to simultaneously achieve high productivity and meet environmental stewardship goals for water use and reduced leaching.

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Although the term consultant is used extensively, the duty of an international horticultural consultant (IHC) lacks precision. We propose that the job of an IHC has many attributes similar to an extension agent in the United States. Accordingly, we highlight the responsibilities of an IHC and put them in a historic and organizational context. Subsequently, we give advice about how to act and behave adequately when going to a new country. We bring in experience from successful IHC and a synopsis of specialist literature. Because we stress the importance of the credibility of an IHC within the farming community he is working with, we emphasize interaction with her/his professional and social environment. An IHC must have a genuine interest in the people being served and their challenges and adequate competence to provide a genuine contribution.

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With the intensification of horticultural research around the world, increasing numbers of scientific manuscripts are being written in English by authors whose primary language is not English. English has become the standard language of science, and English language manuscripts are readily accessible to the global scientific community. Therefore, non-native English speakers are encouraged to publish appropriate studies in English. Reviewers of manuscripts written in English by non-native speakers are encouraged to focus on scientific content and to provide constructive criticisms to facilitate the international exchange of information. Problems associated with writing scientific manuscripts in English can impede the publication of good science in international journals. This article describes problems in horticultural manuscripts that are often encountered by authors who are non-native English speakers and provides suggestions and resources to overcome these problems. References have been selected that provide clear help for authors in horticulture and other plant sciences.

Open Access

Nitrogen fertilizer rates and timings were reexamined for potatoes (Solanum tuberosum L.) under sprinkler irrigation with scheduling by soil water potential. Four potato cultivars were grown on a silt loam soil in eastern Oregon in 1992, 1993, and 1994. Potatoes were submitted to six treatments: four N fertilizer rates (0, 135, 200, and 270 kg·ha-1) and two split application treatments (67 kg·ha-1 applied three times, and 40 kg·ha-1 applied five times). The crop was irrigated when the soil water potential at 0.2-m depth reached -60 J·kg-1. No more than the accumulated evapotranspiration was replaced at each irrigation. Over 3 years, the cultivars had similar responses to N rates and N timing. In 1992, following alfalfa, tuber yield was not responsive to N fertilization. In 1993 and 1994, following wheat, tuber yield was maximized by N at 211 and 175 kg·ha-1. Split applications of the N fertilizer did not increase tuber yield in any year. In 1993 and 1994, the highest tuber specific gravity was obtained with no N fertilization. Nitrogen rates above the optimum resulted in darker frying tubers in 1992 and 1993. The N rates maximizing tuber yield in this study were lower than the rates recommended in the university fertilizer guides.

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Four potato (Solanum tuberosum L.) varieties were grown under four season-long sprinkler irrigation treatments in three successive years (1992-94) on silt loam soil in eastern Oregon. The check treatment was irrigated when soil water potential (SWP) at the 0.2-m depth reached -60 J·kg-1 and received at most the accumulated evapotranspiration (Etc) to avoid exceeding the water-holding capacity of the top 0.3 m of soil. The three deficit irrigation treatments were irrigated when SWP at the 0.2-m depth reached -80 J·kg-1 and had the following percent of the accumulated Etc applied at each irrigation: 1) 100%, 2) 70%, and 3) 70% during tuber bulking with 50% thereafter. Based on regression of applied water over 3 years, potatoes lost both total and U.S. No. 1 yields when irrigations were reduced. Based on regression on applied water, when irrigation was reduced gross revenues declined more than production costs, resulting in a reduction in profits. Leaching potential, as determined by the SWP treatments, was low for all treatments. The results of the study suggest that deficit irrigation of potatoes in the Treasure Valley of Oregon would not be a viable management tool, because the small financial benefits would not offset the high risks of reduced yields and profits from the reduced water applications.

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Onion (Allium cepa L., `Great Scott') was grown on silt loam soils and submitted to four irrigation thresholds (-25, -50, -75, and -100 kPa) in 1992 and six irrigation thresholds (-12.5, -25, -37.5, -50, -75, and -100 kPa) in 1993 and 1994. Irrigation thresholds (soil water potential measured at 0.2-m depth) were used as criteria to initiate furrow irrigations. Onions were evaluated for yield and grade after 70 days of storage. In 1992 and 1994, total yield, marketable yield, and profit increased with increasing irrigation threshold. In 1993, total yield increased with increasing irrigation threshold, but marketable yield and profit were maximized by a calculated threshold of -27 kPa due to a substantial increase of decomposition during storage with increasing threshold.

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Eight winter squash varieties (Table Ace Acorn, Sweet Dumpling, Waltham Butternut, Honey Boat, Sugar Loaf, Spaghetti, Gold Keeper, and Kabocha) were placed in storage 3 weeks after harvested and were stored for 6, 12, or 16 weeks at 5, 10, or 15°C and 50, 60, or 70 percent relative humidity. Before storage Spaghetti squash had low dry weight and low sugars while Kabocha, Sugar Loaf, and Honey Boat had high dry weight and high sugars. Squash of all varieties suffered high spoilage when stored at 5°C. Water losses increased with temperature or with storage at 50 percent relative humidity. Considering both spoilage and water loss, marketable fruit was highest when squash was stored at 10°C or 15°C and 60 or 70 percent relative humidity. Squash sugars were maintained with storage at 5°C and 10%. Squash can be stored for several months at 10°C and 60 to 70 percent relative humidity with little fruit loss or loss of sugar.

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Onion (Allium cepa L.) production in the Treasure Valley of eastern Oregon and southwestern Idaho has been based on furrow irrigation with 318 kg·ha-1 N fertilizer and average yields of 70 Mg·ha-1, but these practices have been implicated in nitrate contamination of groundwater. Drip irrigation, introduced in the early 1990s, has several advantages, including reduced leaching losses. Since onion plant populations and N fertilizer rates can affect economic returns, studies were conducted in 1999, 2000, and 2001 to determine optimum plant populations and N fertilizer rates for subsurface drip-irrigated onion. Long-day onion (`Vision') was subjected to a combination of seven nitrogen fertilization rates (0 to 336 kg·ha-1 in 56-kg increments applied between late May and early July) and four plant populations (185, 250, 300, and 370 thousand plants/ha). Onion was grown on silt loam in two double rows spaced 0.56 m apart on 1.1 m beds with a drip tape buried 13 cm deep in the bed center. Soil water potential was maintained nearly constant at -20 kPa by automated irrigations based on soil water potential measurements at a 0.2-m depth. Onion bulbs were evaluated for yield and grade after 70 days of storage. Onion yield and grade were highly responsive to plant population. Onion marketable yield increased, and bulb diameter decreased with increasing plant population. Within the range of plant populations tested, gross returns were not always responsive to plant population. Returns were increased by the increase in marketable yield obtained with higher plant population, but higher plant population also reduced the production of the largest sized bulbs which had the highest value per weight. Onion yielded 95 Mg·ha-1 with no applied N fertilizer, averaged over plant populations and years. Onion yield and grade were not responsive to N fertilizer rate or interaction of N fertilizer rate with plant population. Preplant soil available N, N mineralization, and N in irrigation water all contributed N to the crop. Onion N uptake did not increase with increasing N fertilizer rate.

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Eleven treatments in 1999 and thirteen treatments in 2000 containing single or combined nonconventional additives from eight manufacturers were compared with an untreated check for their effect on onion (Alliumcepa L.) yield and quality, and for their economic efficiency. The nonconventional additives were tested at commercial rates using the methods of application provided by the manufacturers. The products were applied to soil, foliage, or both. The treatments, including the check, were incorporated into standard cultural practices for onions. All treatments (with exception of an organic fertilizer treatment), including the check, were fertilized based on soil tests. In both years, none of the products evaluated significantly increased onion yield or quality compared to the untreated check. The organic fertilizer treatment, tested in 1999 only, resulted in significantly lower onion yield and size compared to the check. At the application rates used in this study, most of the products supplied plant nutrients or humic acid in amounts insufficient to expect improvements in crop production.

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Sweet worm wood is a source of the anti-malarial plant secondary compound artemisinin. The effects of water stress, nitrogen rates, plant growth regulators, and harvest timing on vegetative growth and yield of artemisinin were tested in separate experiments. In the harvest timing trial, total biomass, leaf yield, leaf artemisinin content and total artemisinin yield increased during the season. The wettest treatment tested decreased the total plant dry to fresh weight ratio, but had no effect on height, total biomass, leaf yield, leaf artemisinin content and artemisinin yield. Nitrogen fertilization increased plant height, but had no effect on total biomass, leaf yield, leaf artemisinin content and artemisinin yield. The plant growth regulators decreased plant height, increased total biomass, but had no effect on leaf yield, leaf artemisinin content and artemisinin yield. The effects of chemical weed control and post-harvest leaf drying will also be discussed.

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