The cap on nitrogen fertilisation is driving forwards optimisations in fertilisation efficiency. Losses caused by denitrification and leaching are having an increased impact on yields and can only be compensated to a limited extent by subsequent fertilisation measures. To ensure high fertilisation efficiency, the nutrients also have to be taken up as completely as possible by the crops. Technical development is therefore additionally focusing on loss minimisation, needs-based dosing of the fertiliser and placement so that it is available to the plants.
Fertilisation need determination
The prerequisite for needs-based fertilisation is knowledge of the quantity of fertiliser required for the specific location. The technology for sensor- and map-based, partial area-specific fertilisation has been available in matured form for a number of years. Map-based, variable fertilisation in particular has only rarely been used in practice so far, however. One key reason for this was the absence of up-to-date satellite images. This has changed since the European Copernicus programme's Sentinel satellites entered operation. The Sentinel-1 satellites with radar cameras and the Sentinel-2 satellites with multispectral cameras are of interest to agriculture (overview). The last of the four satellites was put into operation in March 2017. Their high-resolution imagery meets the requirements of partial area-specific fertilisation, and the frequency of the flyovers increases the likelihood of obtaining images that can be evaluated promptly. The European Space Agency (ESA) provides the images free of charge and also offers tools for evaluation, up to and including the calculation of the NDVI vegetation index. Established companies and start-ups are making intensive use of these options and are offering inexpensive biomass, fertilisation and sowing maps on the basis of the Sentinel data. These are being marketed in the form of cloud-based internet applications for PCs in combination with apps for Android and iOS devices.
Overview: the Sentinel satellites' performance
| Sentinel-1 | Sentinel-2 | |
| Sensor | Radar | Multispectral |
| Altitude | 693 km | 786 km |
| Refresh rate | 6 days | 5 days |
| Maximum resolution | 5 x 5 m | 10 x 10 m |
The combination of current, high-resolution maps together with inexpensive, widespread smartphone technology is also making partial area-specific fertilisation very attractive for small and medium-sized farms. Increased demand for fertiliser spreaders with ISOBUS technology, and perhaps also for pneumatic spreaders, is therefore to be anticipated. A new pneumatic spreader implement was presented at the last Agritechnica, almost certainly as a result of this development. The spreader is scheduled to be launched next year with working widths from 18 to 30 m.
Fertiliser quantitydosing
With these pneumatic spreaders, new dosing systems are able to implement even small-scale variations in the output quantity. In this process, the dosing devices of each individual fertiliser outlet aperture are electrically driven independently of one another and are continuously adjustable. With a voltage of 48 V, the electric drive enables very short adjustment times and therefore fast variation of the fertiliser quantity in the direction of travel. Transverse to the direction of travel, fertiliser output can be varied in 1.2 m wide strips. This leads to significantly higher spatial resolution in comparison with previous solutions.
The specified values are implemented more precisely during fertilisation according to an application map. Excessive and insufficient dosing can be significantly reduced when spreading on wedge-shaped land and around corners. Boundary spreading can also be optimised by adjusting the quantity at the outer fertiliser outlet aperture in combination with a boundary spreading deflector plate.
Fertiliser placement
In recent years, focus has additionally been placed on developments in the area of fertiliser placement. This includes methods such as strip-till and high-precision under-root fertilisation. With the strip-till method for maize, sugar beet, potatoes and, to a limited extent, for cereals and rapeseed, a high percentage of fertiliser is spread close to the plant roots. This minimises the loss of fertilisers that fail to reach the roots.
Studies conducted by Cologne University of Applied Sciences have shown that fertiliser can be saved by further concentrating fertiliser placement even within a row. If the under-root fertiliser is only placed specifically in the vicinity of the seeds in small portions when sowing maize, 25 % of the fertiliser can be saved with the same yield. Yield increases of 6 to 7 % were measured with the same quantity of fertiliser during the three-year trials.
Further technological aids
Despite all of this modern technology, one aspect should not be overlooked: high fertilisation efficiency can only be achieved if the fertiliser spreader is calibrated correctly. Aids that support the driver are available for accomplishing this. Clear progress has also been made in this area. This includes:
- Extensive databases for correct spreader calibration; today, these can also be called up via an app using a smartphone while working,
- Automated GPS-aided partial width and headland switching,
- Radar sensors that continuously register the spreading pattern during operation.
Today, progress in control and regulation technology in combination with high-performance data networks is also enabling the influence of slopes to be taken into consideration during spreading with broadcasters. So far, no system has been able to compensate the changed spraying distance on a slope. A new control system
Dr Norbert Uppenkamp, NRW Chamber of Agriculture, Münster, Germany