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.
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.
Excessive cutting pressure (CP) early in the lifespan of an asparagus (Asparagus officinalis L.) plantation may weaken and reduce yields and quality. The objective of this research was to determine how increasing CP affects yield, quality, and survival of spring-harvested and summer-forced asparagus. `Jersey Gem' asparagus was harvested for 4 years (1999–2002) in spring or summer-forced on 1 Aug. using the following CP (weeks/year from 1st to 4th years, respectively): 2, 3, 4, 6 (low), 3, 4, 5, 7 (medium), and 4, 5, 8, 10 (high). In all harvest years, as CP increased, marketable number and weight increased. Yield in spring harvest seasons significantly increased with each increase in CP. In summer, yield significantly increased only when high CP was used with equivalent yields at low and medium CP. With summer forcing, there were 48% and 55% fewer large spears at medium and high CP, respectively, compared to the same CP used during spring harvest seasons. Stands tended to decrease with CP from 1997 to 2003, but these differences were not significant and not severe enough to kill the plants. Yearly root fructose concentrations (RFC) with all CP increased yearly from 1999 to 2001 and plateaued from 2002 to 2003. From 1999 to 2002, RFC increased 53%, 27%, 13%, and 13% in unharvested control, low, medium, and high CP, respectively, indicating that with a greater CP, RFC decreased. RFC in summer-forced asparagus was significantly less than spring-harvested in 83% of all sample months. RFC in spring-harvested asparagus was similar to unharvested asparagus in February, March, April, November, and December; however, in all other sample months, spring-harvested RFC was significantly lower than unharvested control plants. The highest CP scheme is appropriate for spring-harvested asparagus based on greatest marketable yields and acceptable cull losses. For summer-forced asparagus, the lowest CP scheme is more appropriate based on acceptable marketable yields and to avoid undue plant stress verified by unacceptably large cull losses mostly attributed to spindly spear size and lower RFC.
Increasing the concentration of sucrose in media containing 5 μm ancymidol increased rooting, with about 95% rooting of two asparagus (Asparagus officinalis L.) selections (Guelph-97, ‘Jersey Centennial’) obtained with 7% sucrose. In the absence of ancymidol, there was no evidence that increased sucrose concentration increased rooting. The increased rooting was not due to an osmotic effect, since the replacement of sucrose by an equimolar concentration of mannitol did not improve rooting. Chemical names used; 1-naphthaleneacetic acid (NAA), N-(2-furanylmethyl)-1H-purin-6-amine (kinetin), and α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol).
The estimate of the photosynthetic response to temperature is important for accurate growth predictions in process-based models designed to respond to broad variation in environmental conditions. Several studies have attempted to decipher the temperature and mesophyll response functions for use in the widely used Farquhar et al. (1980) biochemically based photosynthesis model. Unfortunately, published values of Rubisco kinetic properties (Kc and Ko) differ among species. To compound the problem, the methodology used to estimate Kc and Ko has not been consistent. We compared the variation in carbon gain estimates of a whole tree by incorporating the different temperature parameter estimates of Bernacchi et al. (2001, 2003) and Medlyn et al. (2002) into a three-dimensional biological process-based model. In addition, we also investigated the contribution of mesophyll conductance by incorporating Rubisco enzyme kinetics parameters reported by Bernacchi et al. (2002). Temperature parameters substantially influenced our whole tree carbon gain estimates. The variation among model estimates of aboveground net carbon gain was ≈11% for 3-year-old red maple saplings. Variation was even greater when mesophyll conductance was incorporated. The different parameter estimates, if not validated at the whole plant scale, can introduce inaccuracies and exacerbate carbon gain estimates of single plants, stands of plants, and entire ecosystems.
Association, Hillegom, The Netherlands, and the Jac. Th. de Vroomen Bulb Co. of Lisse, The Netherlands, for the special handling of the crowns. Use of trade names does not imply endorsement of the products named nor criticism of similar ones not named. The
1 Professor of Vegetable Crops. Florida Agr. Expt. Sta. Journal Series no. R-00261. Rhubarb crown divisions provided by Nourse Farms, South Deerfield, Mass., and `Victoria' seedlings by Hunsader Farms, Bradenton