Effects of compost on onion quality, yield, and thrips infestation

Although onion, Allium cepa L., production has been enhanced by the addition of organic matter to soil, other reports indicated no effect. In this study, onion plots (var. Sweet Sunrise) were treated with conventional fertilizer, composted sugar mill ash and vegetative yard waste, or fertilizer + compost. Measurements during two consecutive growing seasons in the Lower Rio Grande Valley of Texas were recorded on soil nutrients, nutrients in onion leaf tissue, leaf lengths, bulb yields in terms of numbers and weights in different size classes, and biochemical qualities. Our study demonstrates that the compost enriched soil fertility, particularly P, K, and Zn; percentage N in the onion leaf tissue was increased to the same extent as plants that received fertilizer; and leaves grew as long as in plots with fertilizer. At harvest, small cull bulbs were consistently the most prevalent in the control, and although compost had a positive influence on numbers and weights of marketable bulbs, fertilizer provided the highest yields during the first growing season. During the second season, however, marketable bulbs in composted plots were as abundant as in the plots receiving fertilizer. Treatment effects on thrips-induced leaf scarring were negligible. We conclude that the compost was useful for increasing marketable onion yield, and that effects improved as the compost decomposed over the two consecutive growing seasons.