Tohoku Journal of Crop Science

Dry matter accumulation and its distribution in various parts of corn plants at different levels of phosphorus fertilizer application were traced at the interval of 15 days throughout growing season. The results are as follows. 1. The process of dry matter accumulation of corn plant can be divided into four reasonable distinct periods by the different rates of dry matter accumulation. These are the periods of : (1) slow dry matter accumulation, (2) gradual dry matter accumulation, (3) rapid dry matter accumulation, and (4) dry matter accumulation in grain. 2. A heavy application of phosphorus fertilizer increased not only the total dry matter yields but also grain/stover ratio.

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The percentages and accumulations of N, P and K in the various parts of corn plants at different levels of phosphorus fertilizer application were traced throughout the growing season. The results are as follows. 1. The percentages of N, P and K in all parts of plants, generally, decreased with time later during the growing season. 2. The percentages of total N was the highest in the leaves among the various parts of plants. 3. The percent P was higher in the leaves and grains than in the other parts of plants and a large proportion, more than 70%, of the total P in the plants was in the grain at maturity. 4. The percent K was higher in the leaf sheaths and stalks than in the other parts. At maturity the stalks contained about three-fifths of the total K in the plants. 5. The pattern of N, P and K accumulation in the plants varied some with each other : the most rapid rate of accumulation appeared in K, the next in N and then in P. 6. The amounts of P accumulation increased markedly with the heavy application of phosphorus fertilizer.

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Changes in endogenous auxins in each part of plants were indicated in relation to the stolon development. The sampling times during the stolon development were shown as follows : (A) stolon emergence, (B) stolon linear growth period, (C) just before tuberization, (D) about 1 cm tuber. The very similar tendency of auxin activity in stolons and in shoot apices was shown, i.e., very high just before tuberization and low at 1 cm tuber. The low auxin activity in stolons and shoot apices was suggested to be related with the cessation of growth of the shoot apex and, moreover, the tuber induction.

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At favorable air-and/or soil-temperature for the assimilates to translocate into the tuber, the growth of whole plant was increascd caused probably by the higher photosynthetic rate of leaves. In the regime of this experiment, 17/12-24/24°C (air-soil, day/night temperature) and 24/19-24/19°C were most favorable for both tuber and plant growth. Taking air-and soil-temperature into consideration, the optimum mean temperature for tuber production seemed to be around 20°C. When air temperature is higher or lower than the optimum, dropping or raising of soil temperature by some methods may be very effective in promoting plant and tuber growth.

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