Ground-based solarimetric measurements on Grain Amaranthus(A. cruentus, L) were made at Akure, Nigeria Latitude 7°N; Longitude 5° E), over a growing season. The solarimeters were fitted with gelatin optical filters (Kodak No. 88A) for measurement in the infrared portion of the solar spectrum. Profile measurements within the canopy were also made at full canopy cover. Simulta neous measurements of the leaf area index (LAI), dry matter production (DM), and photosynthate partitioning (PP) were also made. Results show an increase of infrared reflectance from 0.11 to 0.35 at full canopy cover after which it starts a downward trend. The relations between normalized difference vegetation index (NDVI) and LAI and DM were cubic. It was also observed that the normalised difference was also sensitive to the phenological stage of the crop in that it shows a lower rate of increase when the partitioning of the photosynthates began. Transmitted infrared (IR) radiation within the canopy was observed to increase with depth.