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

124 History of the International Rice Research Institute2. a raised-bed treatment in which the surface was above the water level butthe roots could encounter a saturated soil below the bed, and3. alternate flooding and drying.There were no appreciable yield differences in the first two treatments, butthe alternate flooding and drying procedure tended to decrease yields.In 1965, the agronomists constructed a set of bottomless metal tanks fedfrom concrete reservoirs so that they could control the depth of water and thetime of application. The experimental equipment allowed them to measurewater use. These studies, which were continued through 1967, had 8 treatmentsranging from continuous deep (10 cm) flooding to those that allowed thesoil to dry out to the point of real moisture stress before it was flooded again.The results of this work showed that the rice plant could yield well as long asthe soil was not allowed to become dry. Maintaining a moist soil, in the absenceof flooding, did not decrease yields. The ideal treatment from the standpointof both water use and yield was shallow (2.5 cm) continuous flooding. Anotherimportant early finding, during the summer of 1966, was that when plots werebunded but unirrigated, yields were equal to those from fully irrigated plots,whereas unbunded plots of dryland rice gave low yields during the sameseason. This illustrated the importance of storing water in the paddy for useduring dry periods, something Asian rice farmers had known for centuries.Weed controlMoomaw wasted no time in getting research started on the use of herbicidesfor weed control in flooded rice. By late 1962, he had assembled 66 herbicidesfor testing, and by the end of 1963, he was able to report on the performanceof about 100 chemicals. He found that MCPA (4-chloro-2-methylphenoxyaceticacid marketed as Agroxone-4) was the most effective, giving about 95%control of broad-leaved weeds and sedges when applied at the rate of 1 kgactive ingredient/ ha.In March 1964, Moomaw conducted the first training course to be given atIRRI — a weed-control short course, attended by 13 scientists from 5 Asiancountries, to stimulate cooperative research on chemical weed control. Thenext year, uniform cooperative herbicide trials were carried on by many of theparticipants in their own countries.Moomaw had screened hundreds of herbicides by 1966-67 and had testedtheir influence on rice yields, comparing them with two hand weedings. Heproved that although several herbicides available at that time were as effectiveas hand weeding in controlling weeds, the cost was often prohibitive. Hefound, however, that the isopropyl ester of 2,4-D applied 3 days after transplantinggave reasonably good control at low cost, considerably lower than thecost of two hand weedings. Later, beyond the time covered in this chapter,other more effective herbicides at affordable prices became available.Moomaw recognized the importance of weed control in upland (dryland)rice and began studying that problem in 1963. The earliest results were not tooimpressive, but in 1967, a yield of 4,160 kg/ha was obtained in a dryland cropof IR5 rice treated with a preemergence application of pyriclor and molinate,