Farms, sensors and satellites

Using fertilisers Farming practice are changing Growing quality crops in good yields depends on many factors, including adequate amounts of water, air and light. Plants also need nutrients. Nutrients are obtained from the growing medium, usually soil. If there are insufficient amounts of one or more of the required nutrients, fertilisers may be used to supply them. But how do growers know what type of fertiliser to use? where to apply it? how much to apply? Even though growers have known for a long time that yields from a field can vary from place to place, the field was still treated on a ‘field average’ basis. But the liberal use of fertilisers can cause environmental harm and be costly to the grower. Sensors and satellites are helping the decision making. Sensors and satellites Sensors and satellites are changing the way growers go about their business. They are enabling growers to: use less fertiliser, which reduces their costs and reduces potential adverse environmental effects. increase the yield of crops by maximising the potential of each field. More information about EGNOS

Nitrogen sensing Not all systems require satellites Some systems are designed to be carried on board the fertiliser vehicle. The sensor detects and measures reflected electromagnetic radiation from the plants. The information is processed by an on-board computer. This automatically adjusts the rate of fertiliser application in response to the information received. The Yara N-Sensor is an example of such a system.

Sensors Sensing electromagnetic radiation Some sensors can detect and measure electromagnetic radiation. They are used detect absorbed, transmitted and reflected radiation. In a colorimeter or spectrophotometer, they detect and measure electromagnetic radiation in the visible region that passes through an object (transmission). This can be used, for example, to determine the concentration of a solution of a coloured solute. In some other instruments sensors detect and measure electromagnetic radiation that has been reflected from a surface. The nature of radiation reflected from leaves gives important information about the health of the plant. Filter White light source Emits full spectrum of visible light (much simplified here) Light with the same colour as the filter is absorbed Some of the ‘filtered’ light is absorbed by the sample The amount of light that passes through is measured Sample Sensor White light source Green light is reflected, but more importantly for analysis so is some near infrared radiation. The remaining radiation is absorbed or passes through. The light source might be natural sunlight or an artificial source. Sensor Absorbance Reflectance Green leaf

Photosynthesis Relationships Photosynthesis, chlorophyll, reflectance from a green leaf, nitrogen content and healthy plants are closely linked. Reflectance of electromagnetic radiation by green plants is dominated by chlorophyll and the concentration of chlorophyll often correlates closely with the nitrogen content of leaves. Reflectance spectrum of a typical green leaf: Chlorophyll exists in two forms - a and b. Both absorb red and blue radiation, so little of this radiation is reflected from green plants. Chlorophyll is essential for photosynthesis The rate of photosynthesis is highest when electromagnetic radiation between 400 and 500 nm and between 600 and 700 nm. chlorophyll and carotenoids absorb radiation in these regions Rate of photosynthesis (%) High rate of photosynthesis Low rate of photosynthesis Almost zero photosynthesis

What do the results tell us? Absorption, transmission and reflectance Electromagnetic radiation that is not absorbed may pass through the leaf (transmitted); be reflected from the surface of the leaf. Measuring reflected radiation provides information about the chlorophyll content of leaves. In turn this provides information about the nitrogen content of the plants. Interpretation of reflectance spectra The higher the density of green plants the more electromagnetic radiation of wavelengths below the red edge that is absorbed and less that is reflected. the less electromagnetic radiation of wavelengths above the red edge that is absorbed and more that is reflected. So measuring the reflectance of electromagnetic radiation can be used to map the density of crops in a field. This allows growers to match the quantity of fertiliser applied to specific parts of the field. Rate of photosynthesis (%) Red edge % Reflectance Green leaves absorb blue and red light – and these are the wavelengths ( nm and nm) that bring about the highest rates of photosynthesis.

EGNOS Using GPS and sensors in tandem The European Geostationary Navigation Overlay Service (EGNOS) is a European Space Agency (ESA) project. “EGNOS is the first pan-European satellite navigation system. It augments the US GPS satellite navigation system and makes it suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels. Consisting of three geostationary satellites and a network of ground stations, EGNOS achieves its aim by transmitting a signal containing information on the reliability and accuracy of the positioning signals sent out by GPS. It allows users in Europe and beyond to determine their position to within 1.5 metres.” Source: html html EGNOS and precision agriculture EGNOS can help farmers in aerial crop spraying or precision farming. It increases the reliability and accuracy of existing GPS systems. Typically GPS is accurate to 5 to 10 metres. Coupled with EGNOS, an accuracy of 1 to 2 metres is achieved. Enhanced navigational data means enhanced efficiency. Back to Using fertilisers The potential market for EGNOS includes: aeronautics, maritime, land transport and and numerous other diverse potential uses.