INFLUENCE ON GROWTH-CONDITIONS ON THE VALUE OF CRISPHEAD LETTUCE .2. WEIGHT LOSSES DURING STORAGE AS AFFECTED BY NITROGEN, PLANT-AGE AND COOLING SYSTEM

Storage of crisphead lettuce was carried out at 1-degrees-C in an ordi nary cold storage room and in an ice bank cooling system. The plants w ere grown at three plantings at 50, 100, 150 and 200 kg total nitrogen supply per hectare and harvested at two or three different plant ages . The cultivars used were 'Marius' and 'Saladin'. The aim of the exper iment was to prolong the storage and to reduce the losses. After 14 da ys of storage the greatest total weight losses were found at the mid-s eason planting whereas the least total weight loss was found at the la te planting. Ice bank cooling at all plantings reduced the total weigh t loss in comparison to the cold storage. The effect of nitrogen and c ultivar was low. The total weight loss defined as loss due to transpir ation and trimming was neither related to the head weight nor the surf ace area of the heads. A reduced loss with increasing plant age was no t a question of increased transpiration due to surface to volume ratio changes, but may be related to other factors. A lower average total w eight loss was found in the ice bank cooling system compared to the co ld storage, The explanation of this might be the existence of a high r elative humidity in the ice bank storage. To reduce the total weight l oss harvest must take place at the right plant age. No definite growth stage was defined here, but the plants must have reached marketable q uality as the young plants are more susceptible to weight loss during storage. It seems likely that some unknown internal factors in the pla nt were involved in reduction of the total weight loss.