Preharvest effects on postharvest quality of pak choi.
Grant, T.; Faragher, J.; Franz, P.; Tomkins, B.;
Postharvest handling of fresh vegetables. Proceedings of a workshop held in Beijing, China, 9-11 May 2001
2001
บทคัดย่อ
The effects of several preharvest factors on the postharvest shelf life of pak choi (Brassica chinensis cv. Joi Choi) were researched. Water stress was investigated to determine whether it might prolong shelf life by hardening plants before harvest. It was examined in two ways: as sustained stress (100, 500 or 1000 ml water per plant box every 2 days); and as intermittent stress (plants were maintained just above wilting point for 6 days and watering for 10 days before harvest). Intermittent water stress produced effects that were most applicable for commercial plant production. At harvest, fresh weight and relative water content did not differ between stressed and non-stressed plants. Shelf life at 10 deg C of whole plants was not affected by water stress even though stressed plants were greener. The implication of this result is that significant savings can be achieved, as less water can be used during production. Future experiments examining several, shorter cycles of stress might produce further information about the effects of water stress on quality and shelf life. The influence of calcium (liquid calcium sulfate, at 0, 33 or 66 kg Ca/ha) and nitrogen (ammonium nitrate at 0, 45 and 90 kg N/ha) on the growth and storage of plants was also examined. Increased calcium (Ca) alone had no significant effect on plant growth. Increased nitrogen (N) alone increased the rate of plant growth initially but late in plant development the plants suffered leaf chlorosis and necrosis. The optimum combination of Ca and N to maximize shelf life, relative water content, and intensity of green colour was high nitrogen (90 kg N/ha) and either of the two calcium rates examined (33 kg Ca/ha and 66 kg Ca/ha). In summary, limiting water by applying an intermittent water stress and adding significant quantities of calcium in combination with nitrogen can provide savings on costs of irrigation and improve plant growth and shelf life.