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  • Author or Editor: Robert J. Dufault x
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The objective of this research was to determine the least variable method to predict the dates of the first and last broccoli (Brassica oleracea L. var Italica) harvests based on heat unit summation using coefficients of variation (cv). The method with the lowest cv for predicting first harvest was to sum, over days from planting to harvest, the difference between the growing season mean (GSM) temperature and a base temperature of 7.2 °C. If the GSM maximum (max) temperature, however, was >26.7 °C, an adjusted max temperature was calculated by first subtracting 26.7 °C from the GSM max temperature and then subtracting the GSM mean temperature. Then the growing degree days (GDDs) were summed by subtracting the base temperature of 7.2 °C from the average of the GSM minimum (min) and adjusted max temperatures. This method produced a cv of 3.96 compared to 4.13 for the standard method of summing over the entire growing season, the mean temperature minus the base temperature of 4.4 °C. The method with the lowest cv for predicting last harvest was to sum, over days from planting to harvest, the difference between the GSM max temperature and a base temperature of 7.2 °C. If the GSM max temperature, however, was >29.4 °C, the base temperature was subtracted from 29.4 °C and not the actual GSM max temperature. This method produced a cv of 3.71 compared to 4.10 for the standard method of summing over the growing season, the mean temperature minus the base of 4.4 °C.

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Fifty-six field plantings of `Baccus', `Citation', `Packman', and `Southern Comet' broccoli were made in Charleston, S.C., at 2-week intervals from February to November from 1990 to 1992. The objective was to determine broccoli's response to growing season mean (GSM) temperatures for several important market quality characteristics, such as head shape, color, density, leafiness, and bead size. Regression analysis determined whether quality was more affected by GSM minimum (min) or maximum (max) temperature for each head quality characteristic. Head leafiness and density of `Baccus' were insensitive to GSM min (7.0 to 23.5 °C) and GSM max (17.5 to 32.5 °C) temperatures experienced during these years. `Baccus' head color was unacceptable at <20.3 °C GSM max and head shape was unacceptable at <19.8 and >26.8 °C GSM max. `Citation' head color and leafiness were unacceptable at >20.5 and >20.2 °C GSM max, respectively. Head density of `Citation' was unacceptable at <19.2 and >28.9 °C GSM max and head shape was unacceptable at <18.4 and >25.7 °C GSM max. Quality of `Packman' was unacceptable for head color at <21.0 and >27.3 °C GSM max, head leafiness at >32.0 °C GSM max, head density at <8.4 and >18.0 °C GSM min, and head shape at >22.0 °C GSM max. `Southern Comet' head quality was unacceptable for head color at <9.2 and >16.5 °C GSM min, head leafiness at >32.0 °C GSM max, head density at <8.9 and >16.2 °C GSM min, and head shape at <21.0 and >25.3 °C GSM max. GSM min or max temperatures did not affect bead size of any cultivar during any planting time studied.

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The purpose of this study was to investigate the effect of different cutting pressures (CP) of 3,6,9, or 12 spears per plant on `UC 157 F1' asparagus yield harvested in spring or forced in July or August. Ten-week-old seedlings were field planted in March, 1987 and forced to emerge from 1989 to 1993 by mowing fern in separate replicated plots in July or August. Forcing treatments were not spring-harvested. Harvesting was terminated if 1) 30 harvests had occurred or 2) 80% of all plants reached cutting pressure treatment levels before 30 harvests occurred. Forced yields were compared to normal spring harvests. Normal emergence time is from January to March. CP treatments affected yield more than harvest time (HT) during the first three harvest years, but, thereafter, HT treatments affected yield more than CP. The most productive HT/CP treatment combinations varied by harvest year as follows: 1989—spring at 9 to 12 spears per plant, July at 12 spears per plant, and August at 9 spears per plant; 1990—forcing in July or August at 12 spears per plant; 1991—forcing in July at 9 to 12 spears per plant; 1992—forcing in July or August at 9 to 12 spears; and 1993—forcing in August at 9 to 12 spears per plant. Total cumulative yields over the 5 year period were highest with forcing in July at 12 spears per plant and August at 9 spears per plant. The productive lifespan of spring-harvested `UC 157 F1' was only three years because of greater stand loss compared to summer forcing.

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The first objective of this paper is to review and characterize the published research in refereed journals pertaining to the nutritional practices used to grow vegetable transplants. The second objective is to note those studies that indicated a direct relationship between transplant nutritional practices and field performance. The third objective is to suggest some approaches that are needed in future vegetable transplant nutrition research. Even after review of the plethora of available information in journals, it is not possible to summarize the one best way to grow any vegetable transplant simply because of many interacting and confounding factors that moderate the effects of nutritional treatments. It is, however, important to recognize that all these confounding factors must be considered when developing guidelines for producing transplants. After thorough review of this information, it is concluded that transplant nutrition generally has a long term effect on influencing yield potential. Therefore, derivation of a nutritional regime to grow transplants needs to be carefully planned. It is hoped that the information that follows can be used to help guide this process.

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The objective of this study was to determine the effect of forcing summer asparagus (May to October) and age at first harvest after transplanting on yield and quality. Ten-week-old `UC 157 F1' asparagus seedlings were field-planted on Sept. 1986 and forced to emerge from 1988 to 1992 by mowing fern in separate replicated plots in May, June, July, August, September, or October. Forcing treatments were not spring-harvested. Forced yields were compared to normal spring harvests (emerging from January to April). Harvesting began for the first time ≈18 or 30 months after transplanting. Spring 1988 yields were greatest of all, but declined yearly for 5 years. Summer forcing in either July or August maintained acceptable yields through 1992. The warmer climate during summer forcing caused most plants to reach the prescribed cutting pressure (eight spears per plant) within a standard 6-week harvest season. Cooler temperatures during spring harvest seasons slowed spear emergence and prevented the plants from reaching prescribed cutting pressure. Forcing in May and June was too stressful to plant recovery after the harvest season by reducing fern regrowth and increasing plant death. Cooler temperatures during October forcing inhibited spear emergence. Forcing in September yielded less than forcing in July and August, but September asparagus would command higher market prices. There was no advantage at any harvest time to delay first harvests from 18 to 30 months after transplanting. Forcing in July through September has potential as an alternative enterprise in coastal South Carolina.

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Abstract

Pretransplanting nutritional conditioning (PNC) regimes were evaluated for their effects on improving tolerance to transplant shock and increasing early fruit production. Muskmelon seedlings (Cucumis melo var. reticulatus L. ‘Magnum 45’) were fertilized twice weekly with solutions containing N, P, and K to determine nutrient needs required to produce high-quality transplants. Seedling height, stem diameter, leaf area, shoot and root dry weights, leaf number, and shoot: root ratios of 27-day-old transplants increased as N rates increased from 10 to 250 mg liter−1. These growth variables also increased with P from 5 to 25 mg·liter−1 but decreased as P increased from 25 to 125 mgliter−1. Increasing K rates from 10 to 250 mg·liter−1 increased seedling height, stem diameter, and leaf area. Nine PNC regimes ranging from low to high N-P-K status were tested under field conditions to determine any long-term advantage. Generally, as PNC levels increased, transplant shock (percentage of necrotic leaves) increased as measured 12 days after transplanting. However, vining, female flowering, fruit set, and early yields increased as PNC levels increased. A high level of PNC (250N-125P-250K, mg·liter−1) conditioned transplants to overcome shock and to resume growth sooner and yield earlier than those at lower PNC levels.

Open Access

Abstract

‘Utah 52-70R’ celery (Apium graveolens L.) seedlings were fertilized weekly with solutions containing N, P, and Κ to determine the nutrient needs required to produce high quality transplants. As Ν rate increased from 10 to 250 ppm, shoot number, seedling diameter and height, leaf area/seedling, shoot and root dry weight/seedling, and dry weight/shoot increased in 52-day-old seedlings. As P rate increased from 5 to 125 ppm, seedling diameter, height, shoot dry weight/shoot, and leaf area increased, but root dry weight and shoot number were not affected. Nitrogen interacted with P for all growth variables measured. Increasing P rates from 5 to 125 ppm significantly increased shoot number, diameter, height, and shoot and root dry weights only in combination with Ν rates of at least 250 ppm; however, dry weight/shoot, leaf area, and root to shoot dry weight ratios increased with P rates used in conjunction with at least 50 ppm N. Potassium rates from 10 to 250 ppm affected neither the growth variables nor did they interact with P or N. Therefore, to grow high-quality celery transplants, nutrient solutions should contain at least 250N–125P–10K (ppm) if a ver-miculite-peat-perlite medium low in N, P, and Κ is used.

Open Access

The objective of this study was to determine the effect of cutting pressures on fern and crown growth of spring- and summer-harvested asparagus (Asparagus officinalis). Two-year-old `UC 157 F1' asparagus seedlings, grown outdoors in 57-liter pots, were harvested for the first time in spring (Mar. 1988) or summer (July 1988) at cutting pressures of three, six, nine, or 12 spears/plant. Fern was mowed to encourage spear emergence in summer. Cutting pressures had no effect on spear diameter in either season. Summer harvesting required 52% less time to complete than spring harvesting. Fern of spring-harvested plants lived 63 days longer than fern emerging after summer harvests; cutting pressure had no effect on fern lifespan. By Nov. 1988, crown quality and growth, harvest times, and storage root carbohydrates were similar among all cutting pressures; however, carbohydrate content was higher in summer-harvested than spring-harvested crowns. Crowns were cold-stored during Winter 1988 and planted in the field in Spring 1989. Plants harvested in Summer 1988 produced 21% more fern in Summer 1989 than those harvested in Spring 1988. Fern production in 1989 was similar for all cutting pressures.

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