Non-destructive measurement of plant growth and nitrogen status of pearl millet with low-altitude aerial photography

Abstract

Computer based image analysis has led to a widespread use of satellite images and aerial photographs in agriculture. However, the application of remote sensing techniques for non-destructive determinations of plant dry matter and nutrient status in field trials has been limited due to the low resolution of satellite images and the high cost of aerial photographs. A simple method based on 24 x 36 mm low-altitude (50 to 500 m) true colour and infra-red aerial photographs taken from a balloon (low-wind conditions) or a kite (high-wind conditions) was used to determine the total dry matter of coppices of the shrub Guiera senegalensis J. F. Gmel. and widely-spaced pearl millet (Pennisetum glaucum L.) planting hills. Results from field trials showed a close relationship (r2 = 0 84 for G. senegalensis and r2 = 0.74 for millet) between the harvested total dry matter of single plants and the plant canopy area determined from the digital analysis of aerial photographs. For pearl millet, differences in the distribution of vegetation index values determined for individual plots corresponded to variations in the application rates of mineral nitrogen fertilisers and planting densities. The results show a potential of low-altitude infra-red photographs to determine total nitrogen uptake of millet at the field level based on independent assessments of plant dry matter and nitrogen concentration in shoots.