Successive lettuce cultivation on organic substrates

Abstract

The purpose of the present work was to evaluate i the influence of organic compost and soil proportions on lettuce growth in greenhouse and ii - the residual effect of organic fertilization in successive lettuce crops. Six compost:soil proportions were evaluated (100:0, 80:20, 60:40, 40:60, 20:80 and 0:100) in three successive lettuce (cultivar “Monica”) crops under randomized blocks design. Stem and crown diameter, plant height, number of leaves, volume of roots, fresh weight of leaves and the aerial portion, dry weight of leaves, stem, aerial portion, roots and the total dry weight; chlorophyll A, B and total chlorophyll were evaluated. There was a significant interaction between the organic compost dosages and the successive cultivation. The effect of the cultivation periods according to the proportions showed, in a general manner, a tendency to produce higher values of CLB, ALP and DMC in the first cultivation period for the majority of proportions. The best proportion of organic compost:soil was of 60:40, in the first crop. For all successive crops, although a residual effect of the compost was detected, the proportion of 60:40 was not enough to sustain the productivity level of the first crop and therefore requiring supplementing fertilization.