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- Author or Editor: Robert J. Dufault x
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The purpose of this 5-year study was to investigate the effects of different cutting pressures (3, 6, 9, or 12 spears/plant) on aspargus harvested in spring or forced in July or August. `UC 157 F1' seedlings were transplanted in 1987 and clear-cut harvested1 from 1989 to 1993. Forcing plots were not spring-harvested, but allowed to produce fern in spring. Summer spear production was forced by mowing all fern and stalks at ground level on the 1st day of each forcing month. Harvested spears were graded and harvesting ended if either 1) 80% of the plants within each plot reached cutting pressure treatment levels or 2) 30 harvests had elapsed: Yields in 1989 were highest and equivalent for the following: spring-harvested at 9 to 12 spears/plant, July-forced at 12 spears/plant, or August-forced at 9 spears/plant. In 1991, forcing in July at 12 spears/plant yielded more than harvesting in spring or August at all cutting pressures. In 1993, August forcing at 9 to 12 spears/plant produced the highest yields with significantly lower yields from July forcing at all cutting pressures. The 1993 spring yields were very poor due to plant death. Stand losses from 1988 to 1993 were 60%, 40%, and 30% in spring, July and August plots, respectively. Cumulative yields over the 5-year-period were greatest and equivalent for July forcing at 12 spears/plant and August forcing at 9 to 12 spears/plant.
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.
Pretransplant nutritional conditioning (PNC) is defined as select fertilization practices used during greenhouse transplant propagation, condition or predispose the seedlings to tolerate and recover from transplant shock in the field and promote earliness. PNC differs from standard greenhouse fertility practices in many ways. Each crop may require a unique, prescribed NPK PNC regime, rather than “one size fits all” approach. PNC regimes are chosen for crops based on long-term yield superiority in the field and not on the visual appeal of transplants to the human eye. Conditioned seedlings are not hardened with nutrient withdrawal. Research has accumulated over recent years providing new insights to PNC. This will be condensed and reviewed to point out the “pros and cons” of PNC. Possible constraints to commercialization and needs for future research will be discussed.
Short productive lifespan is a major problem with asparagus (Asparagus officinalis L.), whether harvested in the spring or forced in late summer in coastal South Carolina. A modification of the Taiwanese system of mother stalk (MS) culture might enhance asparagus longevity and yield. The objective of this research was to determine if modified MS culture improved plant survival and yields in spring or summer-forced harvests compared with conventional spring clear-cut (CC) harvesting or with nonconventional summer-forced CC harvesting. `Jersey Giant' asparagus was harvested for 3 years (1994-96) using the following harvest systems: 1) spring CC (normal emergence in February in this location); 2) spring MS followed by summer MS (mow fern down on 1 Aug. and establish new mothers); 3) spring MS only; 4) summer CC only (mow fern on 1 Aug. and harvest); and 5) summer MS only. All systems were harvested for ≈7 weeks. All MS plots produced 40 mother stalks per 12-m row length each year before harvesting began. All mother stalks were trellised and tied to prevent lodging. Three-year total yields (kg·ha-1) and stand reduction (%) for nonharvested controls, spring CC harvesting, spring MS culture, spring MS combined with summer MS, summer CC, and summer MS were: 0 and 54%, 1621 and 96%, 779 and 99%, 1949 and 86%, 4001 and 58%, 3945 and 58%, respectively. All spring harvesting systems failed because by midsummer, aged fern, harvest pressures, and, apparently, higher rates of crown respiration reduced crown carbohydrate reserves. Yearly repetition of these stresses ultimately killed the spring-harvested plants. The MS culture did not ameliorate stand loss by significantly increasing carbohydrate reserves. Yields of summer-forced asparagus were consistently acceptable because aged ferns were removed at about the time they apparently became inefficient photosynthetically. After termination of the summer harvest season and with recovery in the following spring, ample carbohydrates were produced well before summer forcing began again in August the following year. Therefore, plant longevity was better sustained by summer forcing than by traditional spring harvesting.
‘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.
‘Southern Comet’ broccoli (Brassica oleracea L. Group Italica) was grown in a NP deficient soilless medium in 15-liter pots for 45 days in a greenhouse averaging 21°C during the growth period. Fertilizer treatments were split-applied and consisted of factorial combinations of 1.9, 3.7, 5.6 g N (total) per pot from urea and 0.07, 0.14, and 0.21 g P (total) per pot from monocalcium phosphate. Potassium from KCl was split-applied at a constant rate of 1.6 g K (total) per pot. Increasing N rate increased head fresh weight, stem diameter, floret total chlorophyll, root and top dry weight (stem, petiole, leaf, and head), plant height, and head quality, and decreased days to heading and to harvest. Increasing P rates increased floret total chlorophyll, height, and root dry weight to a lesser degree than N. For quality broccoli production in the greenhouse, 5.6 g N, 0.21 g P, and 1.6 g K per 15 liter pot were required.
‘Utah 52-70R’ celery (Apium graveolens L.) seedlings were grown in a N- and P-deficient soilless medium amended with N and P slow-release fertilizers (Osmocote) in greenhouses maintained at either 21° to 32°C (warm house) or 14° to 24° (cool house). Generally, as N rate increased from 1.25 to 10 g N/kg of medium, plant stands, chlorophyll, shoot number, plant height, leaf area, and shoot and root dry weights increased; but, from 10 to 20 g N/kg of medium, these variables decreased. As P rates increased from 2.5 to 10.0 g·kg−1 of medium, only chlorophyll content decreased linearly. Temperatures in the warm house generally reduced celery growth compared to the cool house. At the experiment's termination, it was determined that as N and P rates increased, media conductivity, nitrate-N, and phosphorus levels increased, but pH decreased. A N rate of 1.25 and 2.5 g P/kg of medium was adequate to produce quality celery transplants in a cool house.
To reduce transplant shock of bell peppers (Capsicum annuum L.), we tested the effectiveness of pretransplant nutritional conditioning (PNC) as a promoter of earliness and yield. In Expt. 1, `Gatorbelle' bell pepper seedlings were fertilized with N from Ca(NO3)2 at 25, 75, or 225 mg·liter-1 and P from Ca(H2PO4)2 at 5, 15, or 45 mg·liter-1. Nitrogen interacted with P, affecting shoot fresh and dry weight, leaf area, root dry weight, seedling height, and leaf count. In Expt. 2, transplants conditioned with N from 50, 100, and 200 mg·liter-1 and P at 15, 30, and 60 mg·liter-1 were field-planted in Charleston, S.C., and Clinton, N.C. Nitrogen- and P-PNC did not greatly affect recovery from transplant shock. Although N- and P-PNC affected seedling growth in the greenhouse, earliness, total yield, and quality were similar in field studies among all PNC treatments at both locations. PNC with 50 mg N and 15 mg P/liter can be used with this variety and not have any long-term detrimental effects on yield and quality.
Pretransplant nutritional conditioning (PNC) of transplants during greenhouse production may improve recovery from transplanting stress and enhance earliness and yield of watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai]. Two greenhouse experiments (Expts. 1 and 2) and field experiments in South Carolina and North Carolina (Expt. 3) were conducted to evaluate N and P PNC effects on watermelon seedling growth and their effects on fruit yield and quality. `Queen of Hearts' triploid and `Crimson Sweet' diploid watermelon seedlings were fertilized with N from calcium nitrate at 25, 75, or 225 mg·liter–1 and P from calcium phosphate at 5, 15, or 45 mg·liter–1. In the greenhouse, most variation in the shoot fresh and dry weights, leaf count, leaf area, transplant height, and root dry weight in `Queen of Hearts' and `Crimson Sweet' was attributed to N. Cultivar interacted with N, affecting all seedling growth variables, but not leaf area in Expt. 2. To a lesser extent, in Expt. 1, but not in Expt. 2, P interacted with cultivar, N, or cultivar × N and affected shoot fresh and dry weights, leaf count and leaf area. In the field, transplant shock increased linearly with N, regardless of cultivar or field location. The effect of PNC on plant growth diminished as the growing season progressed. For both cultivars at both locations, N and P PNC did not affect time to first staminate flower, fruit set, fruit width or length, soluble solids concentration, or yield. Vining at Charleston for both cultivars was 2 days earlier when N was at 75 rather than 25 mg·liter–1, without further change with the high N rate. At Clinton, the first pistillate flower was delayed linearly the higher the N rate for `Crimson Sweet'. At Charleston, hollow heart in the `Queen of Hearts' increased nearly 3 times when N PNC rate was tripled (from 75 or 225 mg·liter–1), while N had no effect on hollow heart in `Crimson Sweet'. In contrast, at Clinton, hollow heart in either cultivar was affected by P PNC, not N. PNC with 25N–5P (in mg·liter–1) can be used to reduce seedling growth and produce a more compact plant for easier handling, yet not reduce fruit quality or yield.