Replacing the nitrogen nutrition index by the chlorophyll meter to assess wheat N status.

摘要

The performance of cultivars is strongly linked to the growing conditions that vary according to both controlled and uncontrolled experimental factors. Specifically, there is a need to control the efficiency of nitrogen (N) use by wheat., to minimize N losses and deficiency. The N nutrition index (NNI) is a precise indicator of N status but it does not suit the users' practical constraints because it requires time-consuming measurements and destructive plant sampling at a precise growth stage. Studies were conducted to test the soil plant analysis development (SPAD) chlorophyll meter as an alternative to the NNI. The chlorophyll meter is a more convenient, leaf clip-on device that determines the relative amount of chlorophyll present in plant leaves. We first identified which leaf should be used; we then compared SPAD and NNI data from various experiments. We also followed SPAD measurements around flowering time to determine a common time span of measurements for all the cultivars of a trial presenting a wide range of earliness. The results showed a non-cultivar-dependent, exponential relationship between the SPAD index and NNI at flowering. This result implies that the SPAD chlorophyll meter can be used as an alternative to NNI to measure N status in wheat. It was also shown that SPAD measurements can be taken before flowering, e.g. during heading, to characterize N status at flowering. This result provides an organizational leeway to experimenters who can then follow more precisely the N status of their trials. Thus the SPAD index is a good substitute for NNI because it is convenient to use.