Aerial photography to determine fertiliser effects on pearl millet and Guiera senegalensis growth

Variability in plant growth is high on most sandy soils of the West African Sahel, often requiring extensive destructive sampling for the reliable est imation of treatment effects. A non-destructive method using aerial photogr aphs and topographic measurements integrated in a Geographic Information Sy stem (GIS) was evaluated to determine the effects of organic and inorganic soil amendments on the growth of millet [Pennisetum glaucum (L.) R. Br.] an d Guiera senegalensis J.F. Grmel. Based on aerial photographs, quantitative methods were developed to estimate the dry matter of millet plants and Gui era coppices present in the field each year prior to millet sowing. Integra ting digital images of both plant species, measurements of the field's topo graphy and a map of the experimental layout in a GIS allowed successful mon itoring of the growth of both species as influenced by phosphorus applicati on and the shrub-crop interaction. Regressions between the dry matter of Gu iera coppices and the canopy area were good (r = 0.76 to 0.93) and permitte d the calculation of the individual coppice dry matter for the entire field with fewer than 40 destructive measurements. The information on coppices' positions extracted from the aerial photographs and the topographic grid us ed as covariates explained a significant proportion of the millet growth va riability. The use of these covariates also improved the precision of the a nalysis of variance of millet dry matter data by reducing the residual sum of squares by as much as 33% in the first experimental year. The study demo nstrates the potential of non-destructive measurements integrated in a GIS to improve the collection and interpretation of data from field experiments .