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  • Author or Editor: Doyle A. Smittle x
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An irrigation scheduling model for turnip greens (Brassica rapa L.) was developed and validated.. The irrigation scheduling model is represented by the equation: 12.7 (i-3) * 0.5 ASW = 0i-1 + Ei(0.365+0.00154i+0.00011i2) - R - I where crop age is i; effective root depth is 12.7 * (i-3) with a maximum of 300 mm; usable water (cm/cm of soil) is 0.5 ASW; deficit on the previous day is Di-1 evapotranspiration; is pan evaporation (Ei) times 0.365+0.0154i+0.00011i2; rainfall (R) and irrigation (I) are in millimeters. Yield measured as leaf weight, and quality analyzed in terms of color (Gardner XL20 cronameter L, a, b), leaf blade and blade: stem weight ratio were determined. Leaf yield and quality responses were affected by both irrigation and fertilizer rates. Yield increased quadratically as irrigation rates increased from 0 to 190% of the model rate. Maximum leaf yields were produced by irrigations at 100% of the model rate. Leaf quality parameters also tended to change quadratically with irrigation rates. Leaf yield and quality changed quadratically as nitrogen fertilizer rates increased from 80 to 120% of the median recommended N rate for Georgia.

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Abstract

Nitrogen did not influence the severity of leafspots (Cercospora cruenta and C. canescens) or rust (Uromyces phaseoli var. vigna), but these foliage disease were more severe on southernpea plants grown in disk-harrowed treatments than in treatments deep-turned with a moldboard plow. Three applications of chlorothalonil reduced the severity of Cercospora leafspots and rust, but did not effectively control the diseases in all tests. Foliage diseases were less severe on ‘White Acre’ than on ‘Purpose Hull Pinkeye’ southernpea. ‘White Acre’ produced the most foliage in disk-harrowed treatments, and ‘Purple Hull Pinkeye’ was superior in deepturned treatments.

Open Access

Abstract

Dry onions of the Granex type were undercut during harvest operations using both oscillating and rotating bar undercutters. Analyses on cleanliness, damage, and disturbance revealed that operating the rotobar with a rotational speed of 540 rpm, a depth of 25 mm below the soil surface, and a forward speed of 6.4 km·hr−1 ensured the most favorable results of the operating speeds, depths, and forward speeds evaluated. Depth of operation was the most important single factor.

Open Access

Abstract

‘Granex 33’ and ‘Sweet Georgia’ onions (Allium cepa L.) at various stages of maturity were harvested by hand and with a prototype mechanical harvester in 1985 and 1986. Bulbs were evaluated for storage losses and bulb quality. Storage losses of both hand-harvested and machine-harvested bulbs were generally similar and increased with increased maturity. Bulb pungency was not affected by harvesting methods and was least for bulbs harvested when 6% of the tops were down. Total sugar concentration of hand-harvested onions, cured with intact tops, was greater than that of machine-harvested onions, when harvested before any of the tops were down, but sugar concentrations at later maturities were similar. Onions that were harvested when < 13% of the tops were down showed greater dry weight in hand-harvested than machine-harvested bulbs.

Open Access

Measurements of daily, 3-day, and 6-day cumulative pan evaporation using a #2 wash tub or a modified steel drum and a ruler provided an accurate, easy, and inexpensive way to schedule irrigation. Pan factors for these containers, which were covered with a 5-cm-mesh wire under humid climatic conditions, were 1.0 and 1.1, respectively.

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An irrigation scheduling model for turnip (Brassica rapa L.) was validated using a line-source irrigation system in a 2-year field trial. The model used a water balance, a variable root length, and a crop factor function of plant age (i). Evapotranspiration was computed daily as class A pan evaporation times a crop factor [CF(i) = 0.365 + 0.0154i-0.00011i2]. Irrigation according to the model maintained soil water tension at <25 kPa at a 30-cm depth. When rainfall amounts were less than water use, leaf yields responded quadratically to irrigation rates, from 0% to 160% of the model rate, and the highest leaf yield with the lowest water applications corresponded to the model rate. Therefore, this model could replace the “feel or see” methods commonly used for scheduling irrigation of leafy vegetables grown in the southeastern United States.

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Sweetpotatoes [Ipomoea batatas (L.) Lam cv. Georgia Jet] were grown on two soil types in drainage lysimeters under controlled soil water regimes during 1982 and 1983. Water regimes consisted of irrigating the sweetpotatoes throughout growth when soil water tension at 23 cm exceeded 25, 50, or 100 kPa or by allowing a 100-kPa water stress before root enlargement, during early root enlargement, or throughout root enlargement. Water use and marketable yields were greater when sweetpotatoes were grown on a Tifton loamy sand (fine loamy, siliceous, thermic, Plinthitic Paleudult) than when grown on a Bonifay sand (loamy, siliceous, thermic, Grossarenic, Plinthitic Paleudult). Water use, marketable yield, and yield of U.S. #1 grade roots generally decreased when soil water tensions exceeded 25 kPa before irrigation, although soil water stress of 100 kPa during storage root development did not significantly affect yield. Regression equations are provided to describe the relationships of water use to plant age and to compute daily evapotranspiration: pan evaporation ratios (crop factors) for sweetpotatoes irrigated at 25, 50, and 100 kPa of soil water tension.

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Cabbage (Brassica oleracea L.) was grown in drainage lysimeters under controlled soil water regimes during 3 years. Three irrigation regimes were imposed on cabbage grown on two soil types during the spring and fall growing seasons. Irrigation regimes consisted of applying water when the soil water tension at 10 cm exceeded 25, 50, or 75 kPa during crop growth. Yields and water use were highest when irrigation was applied at 25 kPa soil water tension. Regression equations are presented to describe the relationships of water use to plant age and to compute the ratios of daily evapotranspiration to pan evaporation (crop factors) for cabbage grown under the three irrigation regimes.

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An irrigation scheduling model for summer squash (Cucurbita pepo L.) was developed and validated during 1986, 1987, and 1989. The model is represented by the equation: 12.7(i - 4) × 0.5ASW = Di-1 + [E(0.14 + 0.015) - P - I]i, where crop age in days is i; effective root depth is 12.7(i - 4) with a maximum of 381 mm; usable water (cubic millimeter per cubic millimeter of soil) is 0.5ASW, deficit on the previous day is Di-1; evapotranspiration is pan evaporation (E) times 0.14 + 0.015i; rainfall (in millimeters) is P; and irrigation (in millimeters) is I. The model was validated during the three years using a line-source irrigation system with irrigation depths ranging from 5% to 160% of the model rates. Nitrogen rates were 50%, 100%, and 150% of the recommended rate. Marketable fruit yields increased as the irrigation depths increased up to the model rate then decreased with greater water application depths. Marketable fruit yields increased as the N rate increased in 1987 and 1989, but yields were similar at all N rates in 1986. The shelf life of marketable fruits was not influenced by irrigation or N rates.

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`Keystone Resistant Giant' bell pepper (Capsicum annuum L.) was grown in drainage lysimeters under controlled soil water regimes during 1982, 1984, and 1985. Three irrigation regimes were imposed on bell pepper grown on two soil types during spring and fall growing seasons. Irrigation regimes consisted of applying water when the soil water tension at 10 cm exceeded 25, 50, or 75 kPa during crop growth. Yields and water use were greatest when irrigation was applied at 25 kPa. Regression equations are presented to describe the relationships of water use to plant age and to compute the ratios of daily evapotranspiration to pan evaporation (crop factors) for bell pepper grown under the three irrigation regimes.

Free access