A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1980

A field experiment with maize (Zea Mays L) under irrigated condition was conducted on a Sulfic Tropaquept soil situated in the premises of the Asian Institute of Technology, Bangkok, Thailand during the dry season (January to May) of 1980 to study the nature of the yield/response relationship and grain protein quality in terms of its essential amino acid (EAA) composition under 9 different rates of N application with constant levels of P and K and 3 widely varying rates of P and K with constant N application. Two sets of experimental plots, one with the N treatments, arranged in a systematic design, and the other with the P and K treatments, arranged in a systematic factorial design, were included in the study, each, treatment having three replicates. The maximum average grain yield (100% dry matter basis) of 3. 73 t/ha was obtained at an N application of 200 kg/ha. Total dry matter yield (grain + stover) was 14 t/ha for the same treatment. Dry matter yield of grain, stover, and grain + stover decreased at applications of N above this level. The maximum average grain yield for P - K treatment was 3.43 t/ha obtained at the P - K combination of 75 kg P and 225 kg K/ha application rate. The water requirement was found to be decreasing with increasing dry matter yield. The crude protein content (C.P.) and its yield increased with increased rates of N fertilizer application. P or K fertilization appeared to have exerted their influences only indirectly in the C.P. content. Maximum C.P. concentration of12.15% was obtained at N application of 350 kg/ha as well as zero P and zero K application rates. No definite conclusion was made on the shape of the yield/response relationships on the basis of present findings. Concentration of N, P, K, Na, Ca and Mg in the grain and straw were determined. The soil was analysed for N, P, K, Na, Ca, Mg and some other characters. Amino acid composition of the grain protein was analysed to determine the grain protein quality. Lysine, one of the limiting EAA in maize grain protein, decreased with increasing grain protein content. The yield per hectare of the EAA as well as the non-EAA, however, increased with increasing dry matter yield. N, P or K fertilization did not significantly influence the EAA composition in maize grain protein.