Measurement systems for determining crop yields
Data from multiple crop years is extremely relevant when it comes to creating meaningful yield maps. This data pool is used to determine zones that differ with regards to the yield potential. Before farmers can even start to capture this data, they need to have the right measurement technology in the form of sensors and weighing systems in place. Farmers have been recording yield quantities and documenting yield data for some time now. The practice has been developing in parallel with technical advancements in sensor technology.
Another important aspect of yield mapping is the precise positioning of measurement points in the coordinates system for each field. Technologies such as real-time kinematic (RTK) and differential global positioning systems (DGPS) are used for this. They can define the position of a machine to the exact centimetre. Improvements have also been made in this sector over the years, enabling position data to be captured with ever greater precision. DGPS works using static reference stations with precisely defined positions. Measurement stations are used to correct and optimise GPS satellite position data. They are absolutely critical in yield mapping in order to evaluate data. Various systems are available for measuring yield quantities.
Yield mapping is most commonly used in arable farming. High-tech combine harvesters are equipped with a multitude of crop analysis tools. Crop data is continuously recorded via light sensors and power/impulse measurements in the machine’s grain elevator. They provide information about the grain volume and mass. Other sensors generate information about the crop’s moisture content. The measurements can be used to correct yield data so that the overall values can be more accurately illustrated. Data on routes, cutting widths, ground speed and mass flow allow conclusions to be drawn about the acreage performance.
Appropriate technologies such as mobile and stationary weighing systems are also available for grassland and maize harvesting. Mobile systems determine the weight of the crop via sensors installed in the axles of transport trailers and grain wagons. Stationary systems can be used near the field or in the area around silos. However, neither of these systems enable site-specific cultivation because the crop cannot be attributed to an exact position on the field. To solve this problem, forage harvesters record the volume flow of the crop. The flow is determined based on roller position data and the crop intake speed. Calibration is required in order to accurately determine the crop yield. To do this, the actual harvested quantity is weighed on the transport wagon and then entered into the system via the forage harvester. The on-board computer then uses these values to determine the yield data. For ultra-precise results, the calibration should be repeated every time the crop variety or field changes. The values generated for yield mapping as part of this process can also be used for precision farming measures.
With the help of DGPS, the continuously recorded data from sensors and measuring instruments is assigned to a specific point on the field so that it can then be used for site-specific cultivation. As this process uses so-called ‘point data’, the values used for yield mapping must be transformed into field data. We’ll discuss the challenges arising from the interpolation process in the following chapter.