EFFECT OF THE PLANT RAISING ENVIRONMENT, TRANSPLANT WEIGHT AND DATE OF TRANSPLANTING ON THE SUBSEQUENT GROWTH AND DEVELOPMENT OF LEEKS (ALLIUM-PORRUM L) GROWN FOR EARLY PRODUCTION

Leek transplant weight at planting was greater for a given period of growth at 23-degrees-C than at 9-degrees-C but was unaffected by nutrition. A single line fitted to all the data, using a time-scale based on 'effective day-degrees' (with a base of 4-degrees-C and an upper limit of 23-degrees-C) accounted for over 76% of the variance in transplant weight at planting. Plant weight at harvest was positively related to transplant weight and fitting straight lines to each of the early and late harvest data sets from all the experiments accounted for 75% of the variance in plant weight at harvest. There were no 'carry-over' effects of temperature or nutrition from the plant-raising phase other than those on transplant weight. It was calculated, using data from two of the experiments where transplanting date was a factor, that yields fell by between 0.4 to 1.6 t ha-1 for each week's delay in planting over the period early April to mid-June. This loss in yield could be compensated by planting larger plants; 300 g plants could be produced in early August by planting 0.6 g, 0.9 g and 1.7 g plants in mid-April, mid-May and early/mid-June, respectively. The number of plants with flower initials at harvest increased with an increase in transplant weight and exceeded 10% with transplants of 0.5 g fresh weight or more and, for comparable transplant weights, was substantially greater from plants raised at 9-degrees than 12-degrees-C. Flower initials were present even in crops from plants raised at 23-degrees-C. Transplants raised at 9-degrees-C produced up to 30% bolters at harvest but bolters were almost completely absent in crops established from plants raised at 12-degrees-C, 18-degrees-C or 23-degrees-C. Small plants (<0.4 g fresh weight) with 2-3 visible true leaves responded to cold.