Effect of Day Length and Soil Moisture on the Flowering, Seed Maturity and Vegetative Growth in Three Types of White Clover

Abstract

Several environmental factors have been suggested as contributing or diminishing factors for the flowering and seed setting in white clover. BEATTY & GARDNER^<2)> and LAUDE et al.^<11)> pointed out the importance of vernalization prior to reproductive phase. They also mentioned the effect of day length on flowering, saying that the long day condition accelerated flowering and increased flower number of the clover. GIBSON^<7)> and MACCLOUD et al.^<12)> found similar effect of day length in their experiments. BRITTEN^<3)> noticed the effect of temperature on the flowering of white clover in Hawaii. He thought the difference between day and night temperature would be the most important factor for the flowering in stable short day condition. Working on temperature and photoperiod, THOMAS^<15)> and BEATTY & GARDNER^<2)> found closely interrelated effect of the two factors. MILLER et al.^<13)> described the role of soil moisture in clover seed production. High soil moisture tended to reduce flower number and increase seed loss through in-pod germination. Genetically there is a wide range of variation in flowering habit. The strains in lower latitude tend to produce flower profusely than the strains from the north when compared in a short day condition^<1, 4, 8)>. It has been widely believed that the seed production of the clover in Japan would be unpractical because of the high humidity throughout the flowering season. But very few fundamental studies have been so far made on the direct or indirect effect of environmental factors which would be responsible for the difficulty in seed production of white clover in this country. The study reported here had been planned to get the informations of the effect of day length and soil moisture on the balance of reproductive and vegetative phases in different types of white clover. Italian ladino, Wilkla witte weideklaver and Louisiana Nolin's improved white clover were subjected to two levels of day length and soil moisture through-out the year of 1961. Natural day length in Chiba (35°N, d_1) was expanded to the simulated day length in 45°N (d_2) by artificial lighting. Soil moisture in high moisture series (m_2) was kept so as not to reduce the level of 60% of maximum water holding capacity of the soil, whereas low soil moisture series (m_1) was kept untouched. Investigations were made throughout the growing season on following dates : April 25, May 30, July 6, Aug. 8, Sept. 20 and Oct. 30. Flower number and herbage yield were recorded together with the contributing components for both characters. Split-split-plot arrangement made it possible to give not only the effect of main factors but the interactions, if any, between them. Long day treatment increased flower number remarkably in Italian ladino and Wilkla witte weideklaver whereas La-N remained unchanged. Effect of day length was so obvious with the increased rate of 4 times in Italian ladino and 2 times in Wilkla witte weideklaver at their peak of flowering when the number of flowers per square meter was 350 and 480, respectively. In Wilkla witte weideklaver long day treatment made its flowering time earlier. La-N did not react to the day length. Natural day length in Chiba would be enough or more than enough to initiate blooming for La-N. Flower number in La-N was 850 at its peak. Soil moisture in m_1 and m_2 indicated similar moisture level up till May depending on the plenty rainfall in spring, but clear difference was observed by the onset of dry season thereafter. Effect of soil moisture on flower number was not so obvious but high soil moisture tended to reduce flower number and accelerate vegetative growth of the clover. This phenomenon resulted in the failure in maturity of fertilized ovules and reduced the number of plump seeds. Long day treatment reduced leaf size, leaf area index, stolon numbers and diame

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