An adventure in applied science - IRRI books - International Rice ...

120 History of the International Rice Research Instituteshort ones the internodes do not elongate to the extent they do in the tallvarieties. Furthermore, when nitrogen is supplied to the two contrastingtypes, the internodes in the short type elongate little but the tall varietiesgrow much taller, thus increasing their susceptibility to lodging at highfertility levels.• Short erect leaves are associated with high yield potential and nitrogenresponsiveness.• Although tillering is increased by nitrogen applications, varieties differgreatly in their inherent capacity to tiller, and breeders should incorporateheavy tillering in their short, stiff-strawed varieties.• Rice varieties that have high yield potential are those that continue toincrease in dry weight from flowering to harvest — that is, those thathave live leaves and depend largely on carbohydrates manufacturedduring that period to fill the grain.• Superior yielding rice varieties have a high grain-straw ratio (about 1.0).• There is a positive and high correlation between solar energy received bya rice crop from flowering to harvest, and yield. Thus, dry season yieldsare always higher than those in the cloudy rainy season, provided thatirrigation and other cultural practices are properly conducted.• The LAI for short, stiff-strawed varieties that do not lodge can be as highas 6 to 12 without any reduction in yield.• Cooperative studies carried out in various environments from Japan toAustralia showed that higher yields occur when there is a long periodbetween flowering and harvest. However, this appears to be a functionof temperature, and because of the uniformly high temperatures in thetropics, the ripening period remains rather constant, usually varyingonly between 28 and 32 days.Those studies had an important bearing on increasing the yield potential ofthe tropical rice plant. As reported earlier, Tanaka left IRRI in March 1966.Yoshida, who took his place, has continued an imaginative and effectiveresearch program.AGRONOMYFrom the standpoint of permanence, the most significant event of 1962 in theInstitute’s research program was the start of the continuous, high-yield riceexperiment. Moomaw and Wortman designed this study, which, in modifiedform, is still being carried on across the road from the administration building(Chandler Hall).Maximum yield experimentMoomaw transplanted two varieties in the field 8 June 1962 — Chianung 242(a ponlai variety from Taiwan) and FB-121 (a Philippine indica variety).Besides a uniform application of phosphorus, potassium, horse manure, andrice straw, which were plowed under before transplanting, there were 4 levelsof nitrogen — 40, 80, 120, and 160 kg/ha. The spacing was uniform at 20 ×20 cm.