Effects of nitrogen supply for the various stages of growth on the yield and quality of potato tubers

Abstract

Experiments were carried out to clarify the effects of nitrogen supply for the various stages of growth on the yield and quality of potatoes (var. Irish Cobbler) in the sand culture. Seed potatoes were planted late in March (1955) or early in April (1956), and plants were harvested early in July (1955) or middle in July (1956). The concentration of nitrogen in the solution was 140 ppm and other nutrient elements also were supplied sufficiently. The results obtained are as follows.
(1) The emergence of tubers in the minus nitrogen treatment was delayed five days compared with that of the control treatment in 1955. But the difference between both treatments was only two days in 1956 experiment, in which larger seed potatoes were used (seed weight was 42_??_43g in 1955, while about 110g in 1956).
(2) In both years, plants which were withheld nitrogen supply after late in June (almost ceasing stage of top growth) showed earlier yellowing of ower leaves, but their yields did not fall behind the control plants supplied with nitrogen throughout all stages of growth. But, when nitrogen supply was discontinued after late in May (begining stage of tuber thickening), or early in June (vigorously growing stage of both top and tubers), yield decreas-ed considerably. On supplying with nitrogen after early in May (completing stage of emergence), top growth caught up soon with that of the control, but tuber yield did not reach. And yield of plants supplied with nitrogen during the period between early in May and late in June, was almost the same as the yield of the control plants. Further, nitro-gen supply being delayed till late in May, yield lowered considerably.
(3) As to tuber quality, there were no distinct differences in dry matter percentage among the treatments But, in ascorbic acid and total nitrogen, the earlier nitrogen supply was discontinued, or the later nitrogen supply was delayed, the lower were their contents.
In conclusion, the period most needed for nitrogen in this experiment, was between early in May (30_??_40 days after planting) and late in June (about 80 days after planting), and nitrogen supply from planting to emergence was also effective for yield increase. But nitrogen supply after late in June was not effective.