In site-specific management for precision farming there is a demand for sensors that can easily monitor crop nitrogen requirements throughout the growing season with a high resolution. Currently used optical measurement platforms such as satellites, airplanes, and hand-held sensors do not meet the requirements for good site-specific nitrogen management possibilities. An automated sensor system mounted on a tractor is developed and used to detect crop nitrogen status optically. A line spectrograph is used to detect the amount of nitrogen (kg N/ha) and chlorophyll (kg/ha) in a wheat crop (Triticum aestivum L.). By calculating the red edge inflection point of the plant spectra in the images, wheat crop nitrogen stress within small areas in the field can be detected. The spectrograph red edge is highly correlated with nitrogen applied to the wheat crop (in kilograms of N per hectare) (0.90), with the crop nitrogen amount (in kilograms of N per hectare) (0.89), and with the chlorophyll amount in the crop (in kilograms per hectare) (0.86). The average errors when estimating these variables with the red edge inflection point are 0.4% (24.15 kg N/ha), 3% (17.31 kg N/ha), and 8% (14.72 kg/ha), respectively. The average standard deviation of the calculated crop nitrogen inside a plot is 7.78 kg N/ha (6%) and for a nitrogen application rate of 9.22 kg N/ha (6%). The average standard deviation of the calculated chlorophyll inside a plot was 5.87 kg/ha (8%) and for a nitrogen application rate of 6.79 kg/ha (9%). This means that spectrograph red edge measurements of the wheat crop during the growing season are good estimators of crop nitrogen uptake. In this way, it can be an indirect predictor of topdress nitrogen needs.
What is lacking in precision farming at present are more comprehensive and fast non-destructive methods for obtaining the data needed to prescribe varia*ble treatments. In precision farming there is a demand for sensors that can easily monitor crop nitrogen requirements throughout the growing season on a high resolution. Currently used optical measurement platforms like satellites, airplanes and hand-held sensors, do not meet the needs of precision agriculture for good nitrogen management possibilities. An automated sensor system mounted on a tractor was developed and used to detect crop nitrogen status optically. A line spectrograph was used to detect amount of nitrogen (kgN/ha) and chlorophyll (kg/ha) in a wheat crop (Triticum aestivum L.). By calculating the red edge inflection point of the plant spectra in the images, wheat crop nitrogen stress within small areas in the field could be detected. Spectrograph red edge was highly correlated with applied nitrogen to the wheat crop (0.90), with crop nitrogen uptake (0.89) and with chlorophyll amount in the crop (0.86). The average errors when estimating those variables with the red edge inflection point were -0.4% (24.15kgN/ha), -1% (17.25kgN/ha) and -10% (14.74kg/ha) respectively. This means that spectrograph red edge measurements of the wheat crop during the growing season can be a predictor of topdress nitrogen needs.
What is lacking in precision farming at present, are more comprehensive and non-destructive methods for obtaining the data needed to prescribe variable treatments. A farmer needs to be informed in order to be efficient, and that includes having the knowledge and information products to forge a viable strategy for farming operations. Current remote sensing (satellite images) sources are too coarse in multispectral spatial resolution and too infrequent in time to allow detailed tracking of phenological stages during the growing season. In this research very detailed and automated on-the-go optical monitoring of the crop is used for detecting and managing zones with different crop yield potential on a seasonal scale. In particular, reflectance properties are used to identify and evaluate optical indicators of the nutritional status of the crop. These indicators should allow site-specific in-seasonal correction of N-application to come to optimal crop yield all over the field. Based on these indicators, site-specific fertilization is done with a variable fertilizer equipped with DGPS. At the end of the season, the crop was harvested with a combine harvester, equipped with precision farming sensors to map final crop yield. In this way final results could be evaluated and analyzed.
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