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C.C. Shock, E.B.G. Feibert, and L.D. Saunders

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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C.C. Shock, E.B.G. Feibert, and L.D. Saunders

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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C.C. Shock, E.B.G. Feibert, L.D. Saunders, and S.R. James

`Umatilla Russet' and `Russet Legend', two newly released potato (Solanum tuberosum L.) cultivars were compared with four established cultivars (`Russet Burbank', `Shepody', `Frontier Russet', and `Ranger Russet'). Potatoes were grown under four, season-long, sprinkler irrigation treatments in three successive years (1992-94) on silt loam soil in eastern Oregon. At each irrigation, the full irrigation treatment received up to the accumulated evapotranspiration (ETc) since the last irrigation. Three deficit irrigation treatments had progressively less water. The new cultivars `Umatilla Russet' and `Russet Legend' performed as well as or better than the other cultivars in the full irrigation treatment, with `Umatilla Russet' showing a higher yield potential at the higher water application rates than `Russet Legend'. All cultivars produced more U.S. No. 1 tubers than `Russet Burbank', except in 1993, an unusually cool and wet year. `Russet Legend' was the only cultivar showing a tolerance to deficit irrigation. In two out of the three years, `Russet Legend' was as productive of U.S. No. 1 yield over most of the range of applied water as `Shepody', `Frontier Russet', and `Ranger Russet' were at the higher end of the applied water range. Chemical names used: 0,0-diethyl S-[(ethylthio) methyl] phosphorodithioate (phorate); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); and 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1methyl-ethyl) acetamide (metolachlor).

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E.B.G. Feibert, S.R. James, K.A. Rykbost, A.R. Mitchell, and C.C. Shock

Previously published research suggests that the yield and water-use efficiency of C-3 plants can be enhanced through foliar-applied methanol. Potatoes (Solanum tuberosum L. cv. Russet Burbank) grown in Oregon at Klamath Falls, Madras, and Ontario were subjected to repeated foliar methanol treatments during the 1993 season. Methanol was applied at 20%, 40%, and 80% concentration with Triton X-100 sticker-spreader at 0.1%, and methanol was applied at 20% and 40% without Triton X-100. Methanol had no effect on tuber yield, size distribution, grade, or specific gravity at any location. Tuber stem-end fry color showed no methanol response at the two locations where it was measured. Soil water potential (measured at Madras and Ontario) showed no difference in water-use efficiency between methanol-treated and nontreated potato plants.