NONDESTRUCTIVE MEASUREMENT OF PLANT-GROWTH AND NITROGEN STATUS OF PEARL-MILLET WITH LOW-ALTITUDE AERIAL-PHOTOGRAPHY (REPRINTED FROM PLANT NUTRITION FOR SUSTAINABLE FOOD-PRODUCTION AND ENVIRONMENT, 1997)

Computer based image analysis has led to a widespread use of satellite images and aerial photographs in agriculture. However, the applicatio n nf remote sensing technique for non-destructive determinations nf pl ant dry matter and nutrient status in field trials has been limited du e to the low resolution of satellite images and the high cost of aeria l 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 ball oon (low-wind conditions) or a kite (high-wind conditions) was used to determine the total dry matter of coppices of the shrub Guiera senega lensis J. F. Gmel. and widely-spaced pearl millet (Pennisetum glaucum L.) planting hills. Results from field trials showed a close relations hip (r(2) = 0.84 for G. senegalensis and r(2) = 0.74 for millet) betwe en the harvested total dry matter of single plants and the plant canop y area determined from the digital analysis of aerial photographs. For pearl millet, differences in the distribution of vegetation index val ues determined for individual plots corresponded to variations in the application rates of mineral nitrogen fertilisers and planting densiti es. The results show a potential of low-altitude infra-red photographs to determine total nitrogen uptake of miller at the field level based on independent assessments of plant dry matter and nitrogen concentra tion in shoots.