Elwadie, M. 2002. Spatial and temporal dynamics of nitrogen-water interactions in corn in Michigan. Ph.D. Dissertation, Michigan State University, East Lansing, Michigan, USA.

This study was initiated to evaluate sensor-based nitrogen and water application for corn ( Zea mays L.) in Michigan. Our hypothesis was that sensor-based N and water applications are more efficient for corn production than the current N fertilizer and irrigation practices based on mass balance recommendations. Chapter I evaluates the agronomic effects of N-water interactions in corn. Irrigation increased yield in 1999 but not without supplemental N application. Nitrogen effectively increased corn grain yield, but there was no significant difference between N applied at planting, or based on a pre-sidedress nitrate test (PSNT), or sensor-based application. A reflectance-based crop coefficient (Kcr) from green normalized vegetation index (GNDVI) is introduced for estimating crop evapotranspiration. Chapter II evaluates the temporal dynamics and biophysical variables estimation of corn canopy in Michigan. High sensitivity to N centered around 560 and 810 nm spectral bands. These two wavelengths provided the best separation between different N treatments. Green normalized vegetation index GNDVI performed better than all other SVI when correlated to chlorophyll meter readings (R 2 = 0.98). These results suggest that GNDVI could be used to substitute for chlorophyll meter readings in N scheduling. While NDVI and GNDVI reasonably estimated corn leaf area index (LAI), SAVI overestimated LAI. All SVI performed very well in estimating fractional cover (Fc) over the growing season. Chapter III assesses the spatial variability of selected soil properties and landscape attributes and their relationship to corn grain yield. Variability for all properties tested exhibited a strong spatial structure and 50 to 100 percent of the sample variance was spatially dependent and auto-correlated over a range of 5 to 224 m. Ap depth, Ap silt, Bt1 bulk density and Bt1 silt were the only significant factors in explaining yield variation. Corn grain yield and soil properties in Ap and Bt1 horizon exhibited a very strong spatial cross correlation. Fifty to 100 percent of the sample covariance was spatially dependent over a range of 26 to 212 m. Cumulative probability and Spearman rank correlation coefficient, the mean relative difference, and the standard deviation were used to characterize the temporal stability of spatial soil water content and spatial water storage over the growing season.

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