Simple technique for estimating nitrate nitrogen concentration of Italian ryegrass (Lolium multiflorum Lam.) at the heading stage using a chlorophyll meter

A simple technique for estimating the nitrate nitrogen (NO3-N) concentration of crop in a field was developed for diploid Italian ryegrass (Lolium multiflorum Lam.) at the heading stage, using a hand-held chlorophyll meter (SPAD-502). A rapid method for estimating the NO3-N concentration in the crop is required in order to feed cattle safely, since high levels of NO3-N in crops cause the nitrate poisoning of ruminants. The SPAD reading was determined as an average for the middle part of 10 flag leaves. SPAD readings for a variety of Nioudachi were correlated with reduced nitrogen concentrations with the following equation: reduced N concentration (g kg−1 DM) = 0.563 × SPAD reading −11.492 with a coefficient of determination of 0.715. SPAD readings also increased with NO3-N concentrations. However, the relationship did not seem to fit a linear curve. A critical value for the SPAD reading was 47 for a NO3-N concentration of 2.0 g kg−1 DM, a critical value for the acute nitrate poisoning of ruminants. The critical SPAD reading value was applicable for eight of 10 other varieties tested. Yields for Nioudachi were increased with the increase in SPAD readings and maximal yields within a year were obtained with SPAD readings over 45, which were less than the critical value for NO3-N accumulation. Therefore, it is possible to manage nitrogen levels to obtain sufficient yields and prevent acute nitrate poisoning.