30 YEARS FERTILIZATION AND IRRIGATION IN DUTCH APPLE ORCHARDS - A REVIEW

Fertilizer levels increased during the 1960s in The Netherlands because of a move towards all grass orchards in which the grass competed with apple trees for nutrients. During the 70s, many apple orchards kept the soil bare around the trees which lessened the demand for fertilizer. Also the need to avoid storage disorders and improve crop quality prompted a reduction in fertilizer use. Since the late-seventies fertilizer applications have stabilized at a low rate, as a result of the emphasis moving from fruit yield to fruit quality. Due to the prevailing wet weather conditions there was little interest in additional water supply until the mid-seventies. After 1976, an extremely dry year, growers became interested in irrigation. Experiments, in which the fertilizer was broadcast in early spring, showed that additional water promoted shoot growth. Flower-bud formation and therefore production did not always keep pace with the increased vegetative growth. However, fertigation, i.e. adding fertilizer to the irrigation water, not only resulted in strong shoot growth and proper leaf colour, but also in sufficient flower-bud formation. Also with fertigation production was greater than with broadcast fertilization in combination with trickle irrigation. Fertigation may also permit control of the root environment because water and nutrient supply become independent of climatic conditions; this method of fertilizer application may facilitate optimizing the nutrient availability in the root zone, and minimize leaching.