Fusion of Hyperspectral and Thermal Imagery for Evaluating Nitrogen and Water Status In Potato (Solanum tuberosum, L.) for Variable Rate Application.

Irrigation and nitrogen (N) management are among the most important aspects for successful potato production on coarse textured soils in central Minnesota.  Mismanagement of either during critical growth stages can have adverse effects on nitrate leaching and/or marketable tuber yield.  The overall objective of this study was to evaluate the ability of airborne hyperspectral (in the visible and near-infrared spectrum) and thermal imagery to detect spatial and temporal variations in the N and water status for a potato crop.  A field study was conducted in 2010 and 2011 at the Sand Plain Research Farm in Becker, MN on a Hubbard loamy sand soil to evaluate the effects of N fertilizer rate/timing (kg ha^-1 N: 34, 180 split, 270 split, 270 split + soil surfactant, and 270 early), irrigation level (conventional vs. limited), and cultivar (Russet Burbank vs. Russet Alpine) on potato plant canopy temperature & reflectance (from aerial and ground-based sources), leaf conductance, SPAD chlorophyll, petiole & leaflet nitrate, and leaf area index.  The limited irrigation treatment plots were given inadequate irrigation according to the checkbook method, especially in the few days preceding field measurements.  The cumulative water totals (rainfall + irrigation) were 809 mm and 711 mm for the conventional and limited irrigation treatments, respectively.  Aerial imagery was acquired twice on dates that roughly coincided with the beginning of tuber initiation and tuber bulking stages, and other measurements were taken on several occasions.  N stress and cultivar had a significant effect on marketable tuber yield, while water stress did not.  The likely reason for minimal response to water stress was due to above average rainfall in 2010.  Several indices were applied to the hyperspectral and thermal data to investigate the ability of the imagery to detect N and water stress during critical growth stages throughout the growing season.