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2001 ARC Projects |
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Imaging Canopies to Detect Stress Using a Portable Spectrometer |
|
 Glen Ritchie Dennis Wright |
Deficiency symptoms affect the color, vigor, and morphology of stressed plants. One visually identifiable
plant deficiency is nitrogen stress. Nitrogen is a primary constituent in chlorophyll, and nitrogen
deficiency leads to chlorosis (yellowing) in leaves and to stunted growth. The human eye is very
sensitive to green light, but it is difficult to compare plant color at multiple locations or at different
dates visually. Water deficiency also results in stunted growth in plants, but not in decreased plant leaf
chlorophyll concentration. The purpose of the 2001 experiments was to test narrow-band spectrometry, SPAD
chlorophyll measurements, digital photography, leaf tissue sampling, and plant yield as methods for
determining nitrogen stress in spring wheat (Triticum aestivum cv. Westbred 936). Wheat was planted
in test plots in May 2001 and subjected to varying levels of nitrogen stress and water stress with
at least five replicate spectral measurements recorded per treatment on clear, sunny days near solar
noon. Both narrow- and broad-band reflectance data correlated with plant yield and protein (highest r2 = 0.68).
The narrow-band measurements were useful for separating groups of nitrogen-stressed plants from water-stressed plants.
In November 2001, greenhouse test plots with four levels of applied nitrogen in hydroponic solution were planted,
and results from the summer experiment are being validated. Research is ongoing, but spectral trends from
nitrogen-stressed plots agree with the trends observed in the field plots. These experiments suggest that
narrow-band reflectance measurements are useful in remote (above the canopy) detection of plant stress.
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A Midseason Nitrogen Application Based on Remote Sensing |
|
 Glen Ritchie Dennis Wright |
An application of nitrogen (N) late in the season has the potential to increase yield and/or quality of wheat. The objective of this study was to test the use of remote sensing data to quantify the amount of N applied to wheat. Remote imaging was also used to monitor the growth and irrigation of the wheat crop. Four rates of N were applied to plots of Westbred 936 hard red spring wheat under center-pivot irrigation, and each rate was replicated four times for a total of 16 plots. The field (pivot) was divided into four quarters. Two quarters of the pivot containing eight plots were managed through traditional techniques, and two quarters were managed using remote sensing. Five randomly selected points in each plot were selected for both tissue sampling and remote sensing analysis. Water was limiting during the growing season because of the Idaho Power Buyback program. Negligible N stress was detected at jointing except in the plots with no applied nitrogen. An empirical equation relating the Normalized Difference Vegetation Index (NDVI) values to the midseason nitrogen content of the wheat was used to quantify N deficiency for a midseason application and N was applied at heading. Water stress from an irrigation malfunction was identified early in the growing cycle; and, as a consequence was partially mitigated. Harvest results showed significant differences in yield between plots with and without a midseason N application. Three stresses identified through remote sensing and yield monitor analysis were due to (1) topography, (2) water, and (3) nitrogen deficiencies on our plots. Yield correlated well with topography (R2 =0.92) even though the high elevation difference was 12 m. |