Abstract
Experiment were carried out to clarify the effects of nitrogen supplied for the various stages from transplanting to harvesting time, on the growth and yield of onions in the sand culture. In both 1952 and 1955, onion seedlings (Yellow Danvers sown early in September) were transplanted late in No-vember and harvested late in next June, Results obtained were as follows.
1. The bulb yields of plants which were stopped nitrogen supply since middle or late in May (completing stage of top growth) were equal to, or rather exceeded that of control plants supplied with nitro-gen until harvesting time. Plants which were dis-continued nitrogen supply since middle or late in April (beginning stage of bulb thickening), were decreased to some degree in both top growth and bulb yield. And in the treatments in which nitrogen sup-ply were discontinued on and before middle or late in March (beginning stage of top growth), top growth and bulb yields were reduced remarkably, and their bulbs were round-shaped in contrast with flatshaped in the control.
2. Plants which were withheld nitrogen supply until late in February or early in March, and since then supplied with nitrogen, recovered their retar-dation of top growth rapidly and their bulb yields made no great difference compared with that of control. But when nitrogen supply was withheld until late in March, or late in April, bulb yields in these treatments could not catch up with that of control until harvesting time.
3. The treatments of cutting off the nitrogen sup-ply for about one month in the various stages of growth, had no effect on bulb yields at harvesting time.
4. In the tops of control plants, nitrogen and dry matter contents were lower until late in Febru-ary, and increased from Mach to May, especially the increment in April was remarkable. In the bulbs, nitrogen contents increased rapidly together with dry matter contents from middle or late in April, and continued to increase until harvesting time.
5. From results obtained, it is concluded that nitrogen supply from middle or late in March to middle or late in May is most important for growth and yield of onion, while nitrogen supply after late in May, or before early in March is not so import-ant as that for the above-mentioned period.
