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Eric Simonne and Doyle A. Smittle

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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Doyle A. Smittle and W. Lamar Dickens

Instrumented rainfall- and groundwater-protected irrigation shelters were used to establish relationships (daily crop factors) between pan evaporation and daily water use for several vegetables. Use of these daily crop factors (water use/pan evaporation) and pan evaporation data for scheduling irrigations are described. Snap bean (Phaseolus vulgaris L.) is used to illustrate irrigation scheduling by this method. A table of the model output with columnar headings of age, root depth, date, pan evaporation, crop factor, daily water use, cumulative water use, allowable water use, rainfall, and irrigation is presented. When irrigation was applied according to the model, soil water tension was held below 25 db at 6-inch (15-cm) soil depth. With varying irrigation rates under a line-source irrigation system, marketable pod yields were maximized at 100% of the model rate. Marketable yields of summer squash also were maximized when irrigation was applied at 100% of the model rate. Marketable yields of sweetpotato were not affected by irrigation rates ranging from 1% to 177% of the model rate.

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M. Darlene Mercer and Doyle A. Smittle

`Gemini II' cucumber (Cucumis sativus L.) fruits were stored for 2, 4, or 6 days at 5 and 6C in 1989 and for 5 days at SC or 10 days at 3C in 1990. Chilling injury (CI) symptoms were rated after 2 to 4 days at 25C. Cell wall polysaccharide concentrations in the peels and in injured and noninjured portions of the peels were determined only in 1990. High CO2 and low O2 delayed the onset of CI symptoms, but did not prevent symptom development. Chilling injury symptoms increased with longer exposure to chilling temperatures. Solubilization of cell wall polysaccharides was associated with development of CI symptoms. Variations in low methoxyl pectinates accounted for 70% of the variation in CI.

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M. Darlene Mercer and Doyle A. Smittle

`Fry' and `Granny Val' muscadine grapes (Vitis rotundifilia) were stored at 1C for two, four, and six weeks in himidified flow-through atmospheres of air, 0% CO2 - 5% O2, 5% CO2 - 5% O2, 10% CO2 - 5% O2, and 15% CO2 - 5% O2. Weight loss, grade, pH, acidity, soluble solids, sugars and sensory evaluations were made upon removal from 1C storage. Chill injury ratings were made after 0, 24, and 48 hours at 27C. `Fry' muscadine grapes had a better storage life than did `Granny Val'. High CO2 atmospheres extended the storage life of both cultivars. Severe chill injury symptoms resulted after 4 or 6 weeks of 1C storage in air. High CO2 atmospheres inhibited chill injury of both `Fry' and `Granny Val' grapes. No chill injury to either cultivar occurred after six weeks of storage in the 15% CO2 - 5% O2 atmosphere.

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Doyle A. Smittle and M. Darlene Mercer

Two lots of `Granex 33' and a `Walla Walla' lot of onions were stored in a Georgia CA facility designed to produce 1C, 70-75% RH, 3% 02, 5% CO2, 92% N2 and an air flow of 1m3/Mg onions. Subsamples of these lots were also stored in air at 1C. Three lots of `Granex 33' onions and one lot of `Texas 1015Y' onions were stored in a CA facility in Michigan under similar conditions.

About 85% of the onions were marketable after 5 months of CA in Georgia and 2 weeks shelf-life. Less than 25% of the onions stored in air at 1C were marketable after a similar storage and shelf-life period. All `Walla Walla' bulbs decayed.

Shelf-life differences occurred among the `Granex 33' lots grown in Georgia and the 1015 lots grown in Texas after 5 months of CA storage in Michigan. Two of the `Granex 33' lots stored fairly well (70-75% marketable) while the third lots stored less well (40% marketable). The Texas 1015 onions stored poorly (0-15% marketable).

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Charles S. Vavrina and Doyle A. Smittle

Six onion (Allium cepa L.) cultivars were grown during 2 years to evaluate the effects of environment on bulb quality as measured by sugar and pyruvate (pungency) concentrations. Within each year, bulb fresh weight was not affected by cultivar; however, bulb fresh weights were 36% higher in a year when most of the rain fell during maximum bulb expansion. Total bulb sugar concentration and pungency varied among cultivars and years. Pungency was higher and the sugar: pungency ratio was lower in `Texas 1015Y' and `Sweet Georgia' than in `Dessex', `Rio Bravo', 'Hybrid Yellow Granex', and `Granex 33'. Under low S nutrition, market acceptance of “sweet” onion cultivars that vary slightly in nonstructural water-soluble carbohydrates may be assessed more precisely by the sugar: pungency ratio than by sugar or pungency assessments.

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Eric H. Simonne, Doyle A. Smittle, and Harry A. Mills

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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Eric Simonne, Harry A. Mills, and Doyle A. Smittle

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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Doyle A. Smittle, W. Lamar Dickens, and M. Jane Hayes

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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Doyle A. Smittle, W. Lamar Dickens, and James R. Stansell

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.