Net radiation above and within a canopy of sweet corn ( Zea mays L., var. Silver Queen) was monitored during early and late stages of growth in separate plots of the same field. The radiation sensors were mounted on automated reversing carriages which were mounted either at 25 or at 300 cm above ground level. The mounted sensors traversed a 3.3 m span to achieve spatial averaging. Output voltages of each radiation sensor was continuously integrated and recorded at hourly intervals. Early and late plant water stresses were induced by inadequate rainfall and the use of automatic rainfall shelters, respectively. Plant height and leaf area were measured in a plant population of 67 750 plant ha −1. Early drought delayed canopy development while in the late drought treatment the canopy was nearly developed before late drought was imposed. When nonstressed plants were fully developed, net radiation 25 cm above the soil surface was 32% of the above-canopy net radiation. As leaves wilted during early drought, net radiation, at 25 cm above the soil surface, increased from 32 to 46% of that measured above the canopy and increased to 51% due to late drought. The observed net radiation differences were induced by imposed plant water stresses which also had the effect of reducing fresh ear yield by 25 to 45% of the irrigated yield for early and late-stressed treatments, respectively.