Aerial top-dressing, or the spreading of inorganic fertilisers from aircraft, introduces stringent flying conditions at extremely low altitudes. During release of the fertiliser there are large load and centre-of-gravity changes, and aerodynamic effects the cause of which has hitherto been conjectural. The experiments described in this paper were aimed at obtaining a knowledge of the aerodynamic effects of the cloud of falling material beneath the plane, and the effects of air flow through the empty hopper. The implications upon aircraft design are discussed. The high accident rate experienced in this industry emphasises the necessity for the production of a suitable aircraft designed solely for top-dressing.