INTERACTIVE EFFECTS OF AGRONOMIC VARIABLES ON MARKETABLE YIELD OF LEEKS

Two experiments were carried out to study the effects of five agronomic variables on the marketable yield of transplanted leeks [UK]. In the first experiment two cultivars were used, cvs Splendid and Winterreuzen, and the treatments compared three plant-raising systems, two ages of transplant when planted, and two plant population densities, two row spacings and two levels of nitrogen nutrition in the field. In this experiment some treatment interactions were confounded with each other. In the later experiment only cv. Splendid was grown. There were two plant-raising systems, two plant-raising temperatures, two plant-raising nutrition levels, two times of transplanting (63 or 84 days from sowing) and four different sowings (7 and 28 February, 20 March and 10 April 1984). The duration of the growth period in the field was standardized by harvesting each treatment combination on two occasions, 168 and 189 days after transplanting. The results from the first experiment showed that plants raised in modules at high temperature, planted early at a high plant density with higher than normal levels of nitrogen gave high marketable (> 12.5 mm in diameter) yields of 7.31 kg/m2, greater than that from any other treatment combination. The second experiment confirmed these general trends but also showed that the date of transplanting was of critical importance with the earliest plantings in the year giving the highest yields and with later plantings resulting in progressively lower yields irrespective of the way in which the transplants were raised. Comparisons with meteorological data showed that decreasing yields were associated with decreasing values of accumulated solar radiation and accumulated day-degrees during field growth. These results are discussed in relation to other published data. They do not support some of the current recommendations for growing the crop but suggest that much more work needs to be done on production systems for this crop because of the potential for increasing marketable yields.