| Abstract | A field experiment was conducted on the acid sulphate soil of Bangkok plain at the Asian Institute of Technology in summer 1976 in order to
1) investigate the effect of lime (0 and 10 t/ha), phosphorous (O and 54 kg/ha) and nitrogen (O, 20, 40, 60 kg/ha) on the growth, yield and chemical composition at preboom, bloom and maturity of a local soybean variety S.J.2, and
2) develop diagnosis and yield prognosis models based on the chemical composition of young plants at a certain dry matter weight level.
Liming increased the growth, yield and concentration of N, P, K, Ca, and Na and decreased the concentration of Mn, Al, Fe and Zn in the aerial parts of the plant. In the soil, application of lime increased available phosphorous (Bray's II P) and decreased exchangeable Al and Fe. Application of P increased growth, yield and concentration of P in the aerial plant parts. The increase in P concentration was much higher in unlimed than in limed treatments. P-application did not clearly influence the
concentration of other nutrients, apart from Zn, the concentration of which tended to decrease. In soil, Bray's II P, increased by P-application. Increased application of N increased growth, yield and concentration of N, P, K, Mg and Mn and decreased the concentration of Fe, Zn and Na in the aerial plant parts. The general convex yield curve for N was found only in
unlimed treatments while in limed ones the first dose of N decreased the final yield. In soil, N application decreased Bray's II P level in limed treatments and the effect was strongest for the first applied dose of N. The results of the soil analysis for available P (Bray's II P), showed
significant relationship with the uptake of P and yield. Application of lime markedly decreased exchangeable Fe and Al in the soil. Preliminary diagnosis and yield prognosis models demonstrated clear relationship between nutrients applied, chemical composition of young plants and final grain yield. The results of the models were quantitative and testing
of the models by comparing actual yield obtained with the prognosed yield showed high degree of reliability. |