The measurement of nitrogen deficiency in grass swards

Summary

A new expression for the degree of nitrogen deficiency is proposed.Nitrogen stress is defined as the percentage shortfall of relative growth rate (R) of a plant below that which the same plant might attain in the absence of any limitation due to nitrogen supply (R _M ), other conditions remaining unchanged that is,

$$S_N = 100\frac{{R_M - R}}{{R_M }}.$$

Nitrogen stress, was measured in the field in uncut swards ofLolium rigidum at different times, with varied levels of basal fertilizers and differing forms of nitrogen supply.

Because the measurement of S_N is laborious, indirect indices of it were sought. The chemical indices tested were total nitrogen and free ninhydrinnitrogen concentrations in the newly mature leaf. A rapid growth index

$$L_N = 100\frac{{L_M - L}}{{L_M }}$$

whereL is leaf elongation rate andL _M is the elongation rate after a non-limiting dose of nitrogen, was also tested.

S_N can be estimated reliably by the three indices studied over the whole range of experimental treatments employed, and up to about 10 weeks following the emergence of the seedlings. L_N appears to be the best of three.