Remote detection of nutrient and water deficiencies in sugarcane under variable cloudiness

Abstract

Spectral measurements were made in a red (0.63–0.69 μm) and an infrared (0.76–0.90 μm) band over sugarcane using a radiometer mounted on a 4-m aluminum pole. Infrared/red ratios measured over a plot with adequate nitrogen, potassium, and water were significantly higher than those measured over a nitrogen-deficient plot at the 1% level, and higher than those over a potassium-deficient plot at the 10% level. In a second experiment, the infrared/red ratios of water-deficient plots were significantly lower than those for plots receiving adequate water. The measurements were made under conditions of variable cloudiness, ranging from full shade to direct sunlight. Although radiance values changed by a factor of 5 from one measurement to the next, changes in the infrared/red ratio were minimal, indicating that this ratio can be adequately measured under variable irradiance conditions for sugarcane when the plants form complete ground cover.