Ground-based remote sensing of water and nitrogen stress

A ground-based remote sensing system (Agricultural Irrigation Imaging System, or AgIIS) was attached to a linear-move irrigation system. The system was used to develop images of a 1-ha field at 1 X 1 m resolution to address issues of spatial scale and to test the ability of a ground-based remote sensing system to separate water and nitrogen stress using the coefficient of variation (CV) for water and nitrogen stress indices. A 2 X 2 Latin square water and nitrogen experiment with four replicates was conducted on cotton for this purpose. Treatments included optimal and low nitrogen with optimal and low water. ANOVA was not an adequate method to assess the statistical variation between treatments due to the large number of data points. In general, the coefficient of variation of water and nitrogen stress indices increased with water and nitrogen stress. In fact, the coefficient of variation of stress indices was a more reliable measurement of water and nitrogen status than the mean value of the indices. Differences in coefficient of variation of stress indices between treatments were detectable at 3 m grid resolution and finer for water stress and at 7 m grid resolution and finer for nitrogen stress.