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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.
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.
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.
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.
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.
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.
Single centeredness has become an important onion attribute for marketing because of the use of onions in food products such as onion rings. Although onion single centeredness is largely cultivar dependent, it may also be influenced by growing conditions. These trials tested the effects of early-season, short-duration water stress on onion single centeredness. The effects of the short-duration water stress were also evaluated on onion yield, grade, and translucent scale. Translucent scale is a physiological disorder thought to be influenced by water stress. Onions were drip irrigated automatically at a soil water tension (SWT) of 20 kPa and were submitted to short-duration water stress in 2003, 2004, and 2005. Onions in each treatment were stressed once at either the two-leaf, four-leaf, early six-leaf, late six-leaf, or eight-leaf stage and were compared with a minimally stressed control. Onions were stressed by interrupting irrigations until the SWT at a 0.2-m depth reached 60 kPa, at which time the irrigations were resumed. Onion single centeredness was reduced by short-duration water stress in 2003 and 2005. Onions were sensitive to the formation of multiple centers with water stress at the four-leaf to late six-leaf stages. The 2004 growing season was characterized by cool, moist conditions, and water stress did not affect single centeredness. Among all treatments and years, marketable yield was only reduced in 2005, with stress at the four-leaf and eight-leaf stages. The incidence of translucent scale was very low each year and was not related to early-season water stress.
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.
Seven potato cultivars were grown in an adequately irrigated check (100% of crop evapotranspiration replaced at -60 kPa) and three deficit irrigation regimes in order to evaluate varietal response to water stress and to evaluate nitrate leaching below the crop root zone in relation to the irrigation management. Potatoes were grown with sprinkler irrigation on silt loam in 1882 and 1993. Water stress treatments were achieved by partial or complete crop evapotranspiration replacement when soil water potential reached -60 or -80 kPa. In 1992, over all varieties, tuber yield and grade were significantly reduced by the two higher levels of water stress. In 1993, a relatively cool year, yield was reduced by water stress, but grade was not. Tuber internal quality was affected more by variety than by deficit irrigation both years. A comparison of pre-plant and post-harvest soil nitrate and ammonium shows that a small amount of nitrate moved from the top two feet of soil to the third and fourth foot in the check plots. Soil nitrogen accounting for the season showed large surpluses, indicating the importance of natural sources of available nitrogen.
Onions were grown with different soil water potentials as irrigation criteria to determine the soil water potential at which optimum onion yield and quality occurs. Furrow irrigation treatments in 1992 and 1993 consisted of six soil water potential thresholds (-12.5 to -100 kPa). Soil water potential in the first foot of soil was measured by granular matrix sensors (Watermark Model 200SS, Irrometer Co., Riverside, CA) that had been previously calibrated to tensiometers on the same silt loam series. Both years, yield and market grade based on bulb size (more jumbo and colossal onions) increased with wetter treatments. In 1993, a relatively cool year, onion grade peaked at -37.5 kPa due to a significant increase in rot during storage following the wetter treatments. These results suggest the importance of using moisture criteria to schedule irrigations for onions.