Prediction by leaf analysis of nitrogen fertilizer required for winter wheat

In 1966 and 1967, 12 experiments on winter wheat tested five rates of N applied in spring as NH 4 NO 3 . Leaf samples comprising all the above ground vegetation were taken on two dates in spring between 31 March and 18 May from a fixed area of crop grown without fertiliser N; the dry matter yield (DM, kg/ha) and N content (%) were determined. Between the two dates, DM increased and leaf N content decreased. From the response curves for N applied and grain yield, the optimum rate of fertilizer N required for maximum grain yield was obtained. The latter was used as a test of soil N availability and compared with the following values (i) content of N (%) in leaves at each sampling and its rate of decrease—no significant correlation, (ii) yield of leaf DM (kg/ha) at first sampling—no significant correlation, (iii) leaf DM yield at second sampling, significant (r= ‐0.678), and also rate of increase in DM (kg/ha per day, r= ‐0.711), (iv) leaf N offtake (kg/ha N) significant at first sampling (r= ‐0.607), second sampling (r= ‐0.744) and also rate of increase in N offtake (kg/ha N per day, r= ‐0.670). Crop growth in spring was related to N supply and it was shown that DM yield, leaf N offtake and their respective rates of increase could be used to assess the availability of N in the soil and to predict the amount of N fertilizer required in spring to obtain maximum grain yield.