Monitoring the spectral and agronomic behaviour of maize in response to nitrogen fertilisation

Maize is a demanding crop that is responsive to nitrogen fertilisation, and meeting its needs is essential to avoid a loss of productivity or environmental contamination. Monitoring nutrient status during crop development is fundamental for optimising nitrogen fertilisation, and using spectral sensors can help detect spatial variability in the field. Based on this premise, the aim of this study was to evaluate the effectiveness of three low-cost sensors in detecting variability in the spectral and agronomic characteristics of the maize cultivar, BM 3066 PRO2®, induced by different N doses (0, 100, 200 and 300 kg ha-1) under two cropping systems, no-tillage and conventional. The study employed a camera with a sensor in the visible region of the spectrum (RGB), a camera in the visible-infrared region (OCN), both mounted on a drone, and a portable chlorophyll meter. Spatial variability was assessed during the crop cycle using the normalised difference vegetation index (NDVI) and chlorophyll index. The results showed that the NDVI(ON) vegetation index from the OCN sensor was more effective at differentiating the treatments than was the NGR vegetation index from the RGB sensor. Furthermore, the chlorophyll b index was better at detecting variations induced by different nitrogen doses, outperforming the vegetation indices obtained by means of aerial images. The airborne sensors under test are more suitable for detecting early spatial macro-variability, while the chlorophyll meter is more effective at assessing the degree of nitrogen deficiency.