Response of shallots to N, P, and K fertilizer rates

The effects of N, P, and K fertilization on growth and yield of shallot (Allium cepa var. ascalonicum Backer) were studied on a Vertisol in a sub-humid tropical environment of eastern Ethiopia under rainfall and irrigation for three years (1999-2001). Treatments during the first two seasons comprised three N rates (0, 75, and 150 kg ha(-1)), three P rates (0, 25, and 50 kg ha(-1)), and two K rates (0 and 100 kg ha(-1)). During the third season, K treatment was excluded and a higher N and P rate (225 and 75 kg ha(-1), respectively) was introduced. In the rain-fed crop, applied N reduced yield while in the irrigated crops, 75 or 150 kg N ha(-1) increased yield through increased number of marketable bulbs or mean bulb weight. In both the rain-fed and irrigated shallots, P at the rate of 25 kg ha(-1) increased yield and mean bulb weight. Application of N and P slightly increased soluble solids, dry matter, and pyruvate content of bulbs. Bulb N and P contents and estimated uptakes increased with increasing fertilizer rates. Weight loss of bulbs after eight weeks of storage under ambient conditions was higher in N-fertilized bulbs. Application of K did not show any clear effects on growth, yield, or quality of shallots. The study indicated that K was not a limiting nutrient, that N was not required for rain-fed shallot crops, and that P was required both for rain-fed and irrigated shallots.