A COMPARISON STUDY OF THREE TYPES OF N-FERTILIZER RESPONSE CURVES ON VEGETABLES

This study was based on the experimntal data from ADAS．U．K．(1987-1989)．Total yield．dry wieght and marketable yield were selected as Y variables, and N fertilizer applied as X variable for each of eight experiments．Three types of response curves：quadratic Y-b0+b1X+b2X2 (M1),linear plus exponential Y-a+brx+cX(M2) and inverse linear Y-abX/(a+bX)+cX(M3), have been fitted for each of the three variables in order to give a comparison as to which one is the best fit at each site．F test shown that among 60 N response equations fitted by three models．55 passed F0.1 and above significant levels．but linear plus exponential has a maximum average percentage variance accountted for (%v.a.f.-93%) and a minimum average residual variance (15.9). The further t test shown that average maximum yield predicted by M1 was significantly higher than that predicted by M 2 M3．But average maximum N calculated by M 2 was significantly lower than that calculated bY M 1 ＆M 3．Considering modelS maximum value．M2 is suited for calabrese and Chinese cabbage．M3 is suited for calabrese and 1eek．while M1 is suited for all three crops．