The great variability of soil properties in their small-scale distribution requires an adjusted site-specific management to avoid wasting resources, environmental pollution and decreasing soil fertility. Proximal soil sensing is a great opportunity to generate highly resolved soil information at field scale in order to depict the within-field variability.
Geo-electric sensors were the first to be used for vehicle-based soil mapping and have found widespread use in agriculture. However, electrical conductivity is influenced by many soil properties. Therefore, conductivity maps can only be interpreted with additional soil reference sampling. Optical sensors that base on the absorption of light through vibrational excitation of groups of molecules like visible-NIR are also used in this area. To calibrate visible-NIR spectra, extensive reference measurements and signature databases are necessary. Close correlations were found with soil fertility parameters such as organic matter and nitrogen. As a radiometric sensor gamma spectrometry has been used increasingly for soil mapping. Based on the direct measurement of potassium, a connection with plant-available and clay-associated potassium was often found.
On-the-go sensors are tested in field campaigns to investigate the spatial distribution of soil properties. With the help of reference sampling, various sensor outputs are compared with soil analysis results using suitable statistical and geo-statistical approaches. The interpreted, spatially highly resolved sensor signal allows to drive dynamic agro-ecosystem models simulating the spatio-temporal dynamic of soil state variables and to actualize simulated states, such as water and nutrient availability in the respective crop growing phase (DOI: 10.1007/s11119-018-9617-y).