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Ronald D. Morse

Advantages of no-till (NT) production systems are acknowledged throughout the world. During the 1990s, production of NT vegetable crops has increased for both direct seeded and transplanted crops. Increased interest in reduced-tillage systems among research workers and vegetable growers is attributed to: 1) development and commercialization of NT transplanters and seeders, 2) advancements in the technology and practice of producing and managing high-residue cover crop mulches, and 3) improvements and acceptance of integrated weed management techniques. Results from research experiments and grower's fields over the years has shown that success with NT transplanted crops is highly dependent on achieving key production objectives, including: 1) production of dense, uniformly distributed cover crops; 2) skillful management of cover crops before transplanting, leaving a heavy, uniformly distributed killed mulch cover over the soil surface; 3) establishment of transplants into cover crops with minimum disturbance of surface residues and surface soil; and 4) adoption of year-round weed control strategies.

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Ronald D. Morse

Potato (Solanum tuberosum L.) yields in Virginia and other hot climates are considerably lower than in cooler areas, predominately because of high soil temperatures during set and bulking of the tubers. Although organic surface mulches conserve soil moisture and lower soil temperature, often resulting in increased tuber yields, applying organic mulches is commercially cost-prohibitive. Preliminary experiments were conducted in 1995 and 1996 at the VPI&SU Agricultural Research Farm to compare production of `Yukon Gold' potato in no-till (NT) raised-bed systems with standard conventionally tilled (CT) methods. No-till yields were higher than CT both years, although differences were not significant. Based on these data, the NT production system used in these experiments is a viable management option, at least in hot climates such as Virginia. Rainfall during tuber bulking in 1995 and 1996 was above average, even excessive at times, which possibly negated the beneficial soil-cooling and moisture-conserving effects of the in situ mulches on potato yield enhancement. Greater yield increases would be expected in NT plots in normal rainfall years.

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Ronald D. Morse

Conservation tillage systems offer distinct advantages for crop production under erosive and droughty soil conditions. This report contains 4 years of data on the effects of in situ cereal rye and wheat mulches on yield of cabbage (Brassica oleracea L. var. capitata) grown under limited-irrigation, conservation-tillage systems. Three tillage systems were studied: conventional plow-disk (CT); strip tillage (ST) and no-tillage (NT). The summers of 1987 and 1990 were characterized by below-average total rain and periods of prolonged (45 days) of dry weather during head enlargement; cabbage yields were highest in the mulched ST and NT plots. In contrast, the 1988 and 1989 growing seasons were above average in total rain and there were no prolonged periods of dry weather. Cabbage yields were unaffected by tillage treatments in 1988, while, in 1989, yields with NT were 65% and 60% lower than with CT and ST, respectively. A combination of abundant rain, soil compaction, and delayed planting retarded plant growth in the 1989 NT plots, resulting in smaller, less-productive plants than in the tilled ST and CT plots. These data show that: 1) conservation tillage and particularly strip tillage systems are viable options for production of cabbage; and 2) rain-irrigation patterns, site selection, and planting dates are major determinants of the relative advantages of conservation tillage compared to conventional tillage systems.

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James A. Okeyo and Ronald D. Morse

Seed tubers of `Yukon Gold' (Solanum tuberosum L.) exhibit strong apical dominance, resulting in relatively poor stem emergence. Cutting seed tubers to overcome apical dominance in `Yukon Gold' results in irregular, uneven stem emergence. In 1992 and 1993, experiments were conducted to evaluate the effects of dehaulming (excising stems to ground level after field emergence) whole, cross- and longitudinal-cut seed tubers of `Yukon Gold' on canopy growth and tuber yield. For all seed piece types, dehaulming during the first week of field emergence produced uniform plant stands and increased yields of U.S. no. 1 tubers by 16 and 42% and large tubers (> 6.4 cm dia.) by 340 and 64% in 1992 and 1993, respectively. Our data indicate that tuber bulking rate was increased by dehaulming. The possible causes and implications of increased tuber bulking rates in dehaulmed potato plants are discussed.

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Michelle L. Infante and Ronald D. Morse

Experiments were conducted with `BigSur' broccoli (Brassica oleracea L. var. italica) at two sites in Fall 1993 and at two sites in Spring 1994 on a Hayter loam in southwestern Virginia. Our objectives were to determine the effects of tillage main plots (conventional tillage = CT and no tillage = NT) and weed control subplots [no overseeding or preemergent herbicide, oxyfluorofen, red clover (Trifolium pratense L.), `Dutch' white clover (Trifolium repens L.), and hairy vetch (Vicia villosa Roth)] on broccoli yield and weed suppression. In all sites, weed suppression and marketable broccoli yield with NT were equal to or higher than with CT. Overseeded legume living mulches did not affect broccoli yield in any site compared to the control plots and suppressed weeds as well as the oxyfluorofen in three of the four sites. Thus, the NT systems used in these experiments can suppress weeds and produce high broccoli yields. Also, overseeded legume living mulches can be established effectively after transplanting to suppress weeds without reducing broccoli yield. Chemical name used: 2-choro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene (oxyfluorofen).

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Gregory E. Welbaum, Charlie R. O'Dell, and Ronald D. Morse

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Lewis W. Jett, Gregory E. Welbaum, and Ronald D. Morse

Priming, a controlled-hydration treatment followed by redrying, improves the germination and emergence of seeds from many species. We compared osmotic and matric priming to determine which was the most effective treatment for improving broccoli seed germination and to gain a greater understanding of how seed vigor is enhanced by priming. Broccoli (Brassica oleracea L. var. italica) seeds were osmotically primed in polyethylene glycol (PEG 8000) at -1.1 MPa or matrically primed in a ratio of 1.0 g seed:0.8 g synthetic calcium silicate (Micro-Cel E):1.8 ml water at -1.2 MPa. In the laboratory, germination rates and root lengths were recorded from 5 to 42C and 10 to 35C, respectively. Broccoli seeds germinated poorly at >35C. Root growth after germination was more sensitive to temperatures >30C and <15C than radicle emergence. Matric and osmotic priming increased germination rate in the laboratory, greenhouse, and field. However, matric priming had a greater effect on germination and root growth rates from 15 to 30C. Neither priming treatment affected minimum or maximum germination or root growth temperatures. Both priming treatments decreased the mean thermal time for germination by >35%. The greater germination performance of matrically primed seeds was most likely the result of increased oxygen availability during priming, increased seed Ca content, or improved membrane integrity.

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Lewis W. Jett, Ronald D. Morse, and Charles R. O'Dell

There is a strong consumer demand for single-head broccoli (Brassica oleracea L. var. italica) that yields more florets per unit weight than bunching broccoli. Two spatial arrangements (single vs. twin row) and five plant densities (10.8, 7.2, 5.4, 4.3, and 3.6 plants/m2) were examined for single-head broccoli production. Spatial arrangement had no significant effect on any measured attribute, although the twin-row arrangement resulted in less plant damage with each harvest. For exclusive production of quality, single-head broccoli with high yields of marketable florets, 3.6 plants/m2 (46-cm within-row spacing) should be used.

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Lewis W. Jett, Ronald D. Morse, and Charles R. O'Dell

Consumer attitudes and preferences towards fresh market broccoli (Brassica oleracea L. Group Italica) are changing. Consumers desire large-head broccoli with more florets per unit weight, which we term single unit broccoli. Single unit broccoli could be field established by transplanting, alleviating the problems of poor stand establishment encountered with direct-seeded broccoli in the Southeast. The objectives of this research were to determine the feasibility of producing single unit broccoli and the optimal plant arrangement and spacing to maximize the yield of single unit broccoli. Two spatial arrangements (single vs. twin row) and five plant densities (10.8, 7.2, 5.4, 4.3 and 3.6 plants/m2) were examined in 1990 and 1991 for production of single unit broccoli. Spatial arrangement had no significant effect on any measured variable, although the twin row arrangement resulted in less plant damage with each multiple harvest. For exclusive production of high quality, single unit broccoli with high yields of marketable florets, a planting density of 3.6 plants/m2 (46 cm within row spacing) should be used in a twin row arrangement.

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Marshall K. Elson, Ronald D. Morse, Dale D. Wolf, and David H. Vaughan

High summer temperatures may reduce plant stands of direct-seeded fall broccoli (Brassica oleracea var. italica Plenck). The influence of constant and diurnally alternating temperatures in the range of 5 to 42C on germination and emergence of `Packman' broccoli was evaluated. Germination was defined as protrusion of the radicle from the seedcoat, and emergence as 10 mm elongation of the radicle. The range of constant temperatures from 10 to 30C for 14 days was satisfactory for 90% germination and 75% emergence. However, alternating temperatures extended the acceptable emergence range to 5/17 through 20/32C. Since soil temperatures in warm climates often exceed 20/32C during the summer, high-temperature inhibition of seed germination and seedling emergence is a potentially important factor limiting direct-seeded broccoli stands.