The use of optical sensors to measure canopy reflectance and calculate crop index as e.g. normalized difference vegetation index (NDVI) is widely used in agricultural crops, but has so far not been implemented in herbage seed production. The present study has the purpose to develop a critical NDVI curve where the critical NDVI, defined as the minimum NDVI obtained to achieve a high seed yield, will be modelled during the growing season. NDVI measurements were made at different growing degree days (GDD) in a three year field experiment where different N application rates were applied. There was a clear maximum in the correlation coefficient between seed yield and NDVI in the period from approximately 700 to 900 GDD. At this time there was an exponential relationship between NDVI and seed yield where highest seed yield were at NDVI ~0.9. Theoretically the farmers should aim for an NDVI of 0.9 and intervene in case of a lower NDVI, which means to apply more nitrogen (N). However, this might be impossible in some years. From a practical point of view aims are therefore to obtain the highest NDVI as late as possible in the growing season and if NDVI has to increase this is done by an additional N application at a time where the crop is able to take up and utilise the applied N.
Proceedings of the 7th International Herbage Seed Conference, 2010, p. 60-63
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The 7th International Herbage Seed Conference, 2010