Abstract: The preferred embodiments described herein provide an apparatus and method for intersecting a light beam and a focal point of a detector at an object of interest. In one preferred embodiment, an apparatus is provided comprising a first support element and a first member carrying a light source and a detector. The first member is pivotable between first and second positions, and when the first member is in the first position, a light beam generated by the light source and a focal point of the detector intersect at an object of interest carried by the first support element. When the first member is in the second position, the light beam and the focal point of the detector intersect at an object of interest carried by a second support element disposed on the first support element.

Abstract: A method and apparatus for the real time determination and application of optimum amounts of nitrogen fertilizer to corn and other arable crops such as cotton, sugar beats, wheat, etc. by the use of rapid, non-destructive sensors and various fertilizer application methods. In a first embodiment, optical reflectance measurements of the crop canopy and a reference strip at the fertilizer response plateau are taken by sensors carried by a center pivot irrigation system. A sensor controller receives, stores and analyzes the sensor data as well as position data received from a center pivot controller. The sensor controller then sends commands to the center pivot controller to order fertilizer application, as necessary, through the irrigation system. A second embodiment of the invention utilizes a tractor drawn fertilizer applicator with the sensors mounted on the application booms.