Effects of nitrogen levels, harvesting time and curing on quality of shallot bulb

Optimization of nitrogen (N) fertilization levels, harvesting stages and curing treatments are among the management practices used for onion bulbs. Field and laboratory experiments were carried out to evaluate the effects of four levels of N application, three harvest stages and two curing levels on yield, bulb quality and shelf life of local shallot cultivar. Results of the study showed that increasing in the N application rate up to 100 kg N ha-1 and delay of harvesting up to 100% top fall, bulb yield of shallot increased considerably. A yield increase of 149, 68 and 72% at the 50, 75 and 100% top fall at harvest on fertilized relative to unfertilized plots. While increasing N levels showed proportional increase in the bulb pungency levels, it did not impact significantly the dry matter, total soluble solids, total sugars and reducing sugars of shallot bulbs either at harvest or during storage. However, there was associated increment in percent bulb rotting and sprouting, loss in bulb diameter, bulb weight loss and unmarketability with increased N application. Harvesting at 75% top fall showed better dry matter content of bulbs, reduced percent rot, sprouting and weight loss and improved marketability of bulbs. Interaction effects of N rates and harvest stage were observed in percent bulb rotting where the highest incidence was in 150 kg N ha-1 and 50% top fall harvest treatments and the least in unfertilized plot harvested at 100% top fall. The result of this study has shown N application in the range of 50 - 100 kg N ha-1, harvesting at 75% top fall and curing bulbs before foliage removal is a good compromise for yield and post harvest quality and shelf life of shallot bulbs under ambient storage conditions.