The Use of Near-Infrared Sensor Technology for Soil Test-Based Decision Making in Agriculture

Keywords: near-infrared spectroscopy, soil testing, sensor, precision agriculture.

Fertilisers are a major cost item for almost all farmers all over the world. The vast majority of farmers apply fertilisers, but only a fraction of these farmers optimise the application rate to the crop needs in relation to their soils’ fertility. This problem is particularly evident in Sub-Saharan Africa, where farmers are often barred from soil testing services because of financial constraints (too expensive), logistic constraints (too far away), or simply because it is unavailable. In developed countries, a transition is occurring towards circularity and precision farming, where insights into soil fertility variations in space and time are required. In both cases, the use of sensor technology may be relevant because of its mobility, affordability and lack of consumables.

Near Infrared (NIR) spectroscopy has been known to soil scientists for years, especially in the area of soil carbon monitoring. This is because NIR directly resonates to chemical bonds in organic matter. For in-field use of NIR spectroscopy to determine nutrients in moist soils, several elements are required:

• A high-quality sensor in a fool-proof device.

• A clean, and sufficiently large calibration database with spectral readings and reference data.

• Advanced statistical models to convert spectral readings into desired parameters using the calibration database.

• Quality checks and corrections, e.g. for moisture content.

• Agronomic interpretation of results.

• Presentation of advice in reports based on results and user needs.

This paper gives an overview of what these elements entail, the potential of NIR sensors for in-situ soil measurements and an example from the field. In short, the potential for soil testing using NIR technology is abundant, but introducing an innovation is more than just a technical endeavour.

C. van Beek1, A.M.D. van Rotterdam2

1 AgroCares, Nieuwe Kanaal 7, Wageningen, The Netherlands.

2 Nutrient Management Institute (NMI), Wageningen, The Netherlands.

22 pages, 9 figures, 3 tables, 19 references