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Title: Quickbird satellite versus ground-based multi-spectral data for estimating nitrogen status of irrigated maize

Author
item Bausch, Walter
item KHOSLA, RAJIV - COLORADO STATE UNIVERSITY

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2009
Publication Date: 8/1/2009
Citation: Bausch, W.C., Khosla, R. 2009. Quickbird satellite versus ground-based multi-spectral data for estimating nitrogen status of irrigated maize. Precision Agriculture. 11:274-290.

Interpretive Summary: Nitrogen (N) use efficiency, defined as percent of applied fertilizer N recovered in the aboveground crop biomass during the growing season, in cereal (corn and wheat) production on a worldwide basis has been reported at 33%. This low efficiency can be related to several factors such as farmers grossly overestimating yields when using yield-based N fertilizer recommendation algorithms, uniform application of N fertilizer across an entire field ignoring areas with high residual soil N, and poor synchronization of N application with crop N demand. Considerable research has been conducted to develop remote sensing techniques for assessing plant N status. Ground-based sensors mounted on high-clearance vehicles have been utilized to assess and map plant N status and to apply N fertilizer during the growing season when needed by the crop and where needed within the field to improve N use efficiency without sacrificing crop production. A limitation to mobile ground-based systems is the time required to acquire data from an entire field. An image-based remote sensing platform would acquire data for an entire field instantaneously. QuickBird, a commercial satellite, has provided new opportunities for remote sensing applications in agriculture. Thus, the objective of this study was to compare corn plant N status assessment from QuickBird satellite data to a mobile ground-based sensor system. Data were acquired in a commercial center-pivot irrigated corn field in eastern Colorado with both systems on the same day. Five attempts were made to acquire data during the vegetative growth period. Unfortunately, cloud cover obscured the field on the first and last attempts rendering the satellite images useless. Clear sky conditions prevailed for the other three dates. Comparison of several vegetation indices calculated from QuickBird and ground-based sensor data resulted in one vegetation index that statistically had a 1:1 relationship between the two systems. A quantitative assessment of N sufficiency maps generated from this index ranged from 79 to 83% similarity based on areal agreement. Our results indicate that QuickBird satellite data can be used to assess irrigated corn N status and its variability within a field for in-season N management assuming cloud cover is not an issue.

Technical Abstract: In-season nitrogen (N) management of irrigated maize (Zea mays L.) requires frequent acquisition of plant N status estimates to timely assess the onset of crop N deficiency and its spatial variability within a field. This study compared ground-based Exotech nadir-view sensor data and QuickBird satellite multispectral data to evaluate several green waveband vegetation indices to assess the N status of irrigated maize, and determine if QuickBird multispectral imagery could be used to develop plant N status maps as accurately as those produced by ground-based sensor systems. The green normalized difference vegetation index normalized to a reference area (NGNDVI) clustered the data for three clear-day data acquisitions between QuickBird and Exotech data producing slopes and intercepts statistically not different from 1 and 0, respectively, for the individual days as well as for the combined data. Comparisons of NGNDVI and the N Sufficiency Index produced good correlations that ranged from 0.91 to 0.95 for the V12 and V15 maize growth stages and their combined data. Nitrogen sufficiency maps using NGNDVI to indicate N sufficient (= 0.96) or N deficient (< 0.96) maize were similar for the two sensor systems. A quantitative assessment of these N sufficiency maps for the V10 to V15 crop growth stages ranged from 79 to 83% similarity based on areal agreement and moderate to substantial agreement based on the kappa statistics. Results from our study indicate that QuickBird satellite multispectral data can be used to assess irrigated maize N status at the V12 and later growth stages and its variability within a field for in-season N management. The NGNDVI compensated for large off-nadir and changing target azimuth view angles associated with frequent QuickBird acquisitions.