A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science of the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M.Sc.) - Asian Institute of Technology, 1976

Quantitative methods of evaluating and controlling the nutritional status of spring sown cereals on the basis of their chemical composition has been satisfactorily applied to agricultural practice in some European countries. Since the growth conditions in Thailand are in favour of such methods and since the rice yields are very low the possibility of transferring the method, to paddy was investigated. In field experiments, urea was applied to paddy in 4 amounts, all given at transplanting time or half of the amounts given at transplanting time and the other half at maximum tillering stage. Chemical composition of the aerial parts of plants. were determined periodically during the growth period and relationships between the chemical composition at a fixed dry matter weight level and N application on the one hand, and chemical composition of final yield on the other hand, were studied. The relationships were in principle similar to those found in the crops in Europe making it possible to transfer above methods to paddy cultivation and to develop preliminary models of (1) correcting the chemical composition of the young rice plant from one dry matter weight level to another (2) diagnosis of nutritional status of the young rice plant together with yield prognosis and (3) N therapy in form of N topdressing in order to control the chemical .composition of the growing crop with the aim of enlarging and improving the grain yield, Further, it was shown that splitting up of the N application in basal dressing and topdressing was superior to undivided N-fertilization meaning that N topdressing, which is the necessary procedure in using above methods is also the best.