A method of and apparatus for performing a topdressing operation on an agriculture field have been provided. The method comprises the steps of: individually and continuously taking pictures of crops planted on a field to obtain crop picture data; processing the crop picture data of each crop to investigate the growing state of each crop; performing a topdressing operation in view of the growing state of each crop. The apparatus comprises a movable main body such as a tractor; a topdressing device provided on the rear side of the movable main body; a video camera provided on the front side of the movable main body; a picture data processing computer adapted to process picture data fed from the video camera so as to measure the leaf size of each crop; a topdressing operation controlling computer adapted to produce a command to the topdressing device to control an amount of a fertilizer to be applied to a crop.