The objectives of this research were 1) to determine if reflectance measured by proximal sensing devices can differentiate between corn nitrogen (N) and water deficiency; and 2) to estimate corn water use in the form of evapotranspiration (ET) across varying degrees of nitrogen (N) and water stress and relate ET to total N uptake across the season. At a single location, an Unmanned Aerial Vehicle (UAV) was used to capture spatially sensitive canopy reflectance from experimental units differentiated by levels of water and N deficiency. Reflectance was measured across different growth stages and used to generate a Combined Index (CI) based on the Normalized Difference Red Edge (NDRE), Green Leaf Index (GLI), and Blue Reflectance Index (BRI) consisting of water stressed, high N stressed, medium N stressed, and non-stressed categories. The CI successfully identified 90% of treatments to the correct category within the experimental treatment structure but was not as successful at two validation sites. This study found that N and water-induced differences in corn productivity can be differentiated in-season by a combination of reflectance indices under narrow cropping system circumstances, but that NDRE alone provides superior information under a broader set of contexts. For the second objective, frequent soil moisture measurements and irrigation data was used to estimate ET using a soil water balance method. Despite differences in absolute N uptake and ET across treatments, the final cumulative ET relative to each treatment was highly correlated to the seasonal relative total N uptake, regardless of stress type or degree (r2=0.92, p < 0.001). This indicates that water use and N uptake are highly connected and should be integrated when making management decisions in corn. Decision-making tools used to schedule irrigation can be used to schedule N application timing and amount.
|Advisor:||Lundy, Mark E.|
|Commitee:||Gilbert, Matthew E., Kisseka, Isaya|
|School:||University of California, Davis|
|Department:||Horticulture and Agronomy|
|School Location:||United States -- California|
|Source:||MAI 82/1(E), Masters Abstracts International|
|Subjects:||Agronomy, Agriculture, Remote sensing|
|Keywords:||Corn, Evapotranspiration, Nitrogen stress, Reflectance, UAV|
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