Use of active canopy sensors to discriminate wheat response to nitrogen fertilization under no-tillage

ABSTRACT Spectral reflectance sensors may be useful in discriminating biomass and nitrogen status in plants. A field experiment was carried out on a loamy Typic Hapludox under no-tillage in Ponta Grossa, Parana State, Brazil, aiming to evaluate the efficiency of active canopy sensors (GreenSeeker 505 and Crop Circle ACS-470) to discriminate wheat response to nitrogen fertilization by determining the dry mass, nitrogen status, and grain yield. A randomized complete block design was used and four treatments were replicated 12 times. The treatments consisted of nitrogen application, as urea, at the rates of 0, 50, 100, and 150 kg ha-1. The nitrogen rates were applied in topdressing at tillering of wheat crop. The readings from the sensors were sensitive to changes caused by nitrogen rates application and yet had close and significant correlations with the dry biomass production and nitrogen uptake by wheat plants. GreenSeeker 505 and Crop Circle ACS-470 sensors showed similar efficiency in discriminating biomass production and the nutritional status in the wheat crop related to nitrogen. Wheat grain yield was high and it did not follow the gains in the production of dry mass in the shoot.