Soil property sensing for site-specific crop management

Site-specific crop management (SSCM) aims to improve production efficiency by adjusting crop inputs, especially fertilizers and agro-chemicals, to varying local conditions within a field. Sensors are needed to obtain site-specific data on factors affecting crop growth and yields, such as nutrient status, weed pressure, soil moisture status, landscape position, soil organic matter (SOM) content, soil acidity, and depth to a restrictive layer. Two SOM sensors have been licensed for commercial development: (1) a single-wavelength sensor that must be recalibrated for the soils and moisture conditions that prevail at the time of use, and (2) a multiple-wavelength sensor which can utilize a single calibration to predict SOM over a range of soil moistures and a range of soil types that occur within a geographical range of several hundreds of kilometers. The single-wavelength sensor requires operator acceptance of the need for frequent recalibration, but is relatively inexpensive and rugged. The multiple-wavelength sensor uses a single calibration applicable over a broader range of soil types and soil moistures, and can also be used to sense soil moisture and cation exchange capacity (CEC), but uses complex technology. A simple inexpensive sensor that can classify soils according to soil moisture has also been developed. Sensors for other soil parameters are being sought, and progress has been reported on nutrient and depth-to-claypan sensing.