N–P–K FERTILIZER EFFECTS ON YIELD, COMPOSITION AND RESIDUES OF LETTUCE, CELERY, CARROT AND ONION GROWN ON AN ORGANIC SOIL IN QUEBEC

Vegetable response to fertilizer treatments of a well decomposed organic soil over a 4-yr period showed potassium as the primary nutrient to be first in short supply for celery (Apium graveolens L.), carrot (Daucus carota L.) and lettuce (Lactuca sativa L.). Onion (Allium cepa L.) yields were depressed on the addition of N, P and K in the 1st yr of the experiment, and subsequently did not respond significantly. Only after 4 yr of cropping were there significant differences between plots of celery, carrot and onion receiving no fertilizers and those receiving N and P annually. After 4 yr cropping without the addition of commercial fertilizers, carrot was the crop showing the greatest reduction in yield. With respect to dry matter produced that normally would be left on the land as crop residues, the average for celery, carrot and lettuce was 3.66, 3.60 and 2.03 t/ha respectively. The percentages of the total N, P and K taken up by whole carrot plants and removed in the harvested portion of the crop were 53.3, 51.1 and 51.8%, respectively. Comparable figures for celery were 49.3, 47.0 and 49.5%, respectively; and for lettuce 34.9, 47.9 and 26.7%, respectively. Data are also provided for the total uptake and removal of Ca, Mg, Mn, Zn, Cu and B by carrot, celery and lettuce.