Paul Drummond

An On-The-Go Spectral Reflectance Sensor for Soil

Laboratory based near infrared spectroscopy (NIRS) has demonstrated good predictive capability for many important soil constituents. Less is known about the feasibility of performing the spectroscopic measurements in a field setting. This paper presents some results of an initial field test of a mobilized in-situ NIRS device. The results demonstrate good pass-to-pass repeatability and meaningful qualitative images. Locally weighted principal component regression was used to develop calibration models relating the reflectance data to levels of soil organic carbon, nitrogen, moisture and pH. The calibrations were used to create constituent maps for a field in central Iowa and compared to images derived from intensive sampling and laboratory analysis.

Soil Profile Measurement of Carbon Contents using a Probe-type VIS-NIR Spectrophotometer

An in-situ probe-based spectrophotometer has been developed. This system used two spectrometers to measure soil reflectance spectra from 450 nm to 2200 nm. It collects soil electrical conductivity (EC) and insertion force measurements in addition to the optical data. Six fields in Kansas were mapped with the VIS-NIR (visible-near infrared) probe module and sampled for calibration and validation. Results showed that VIS-NIR correlated well with carbon in all six fields, with RPD (the ratio of standard deviation to root mean square error of prediction) of 1.8 or better, RMSE of 0.14 to 0.22%, and R 2 of 0.69 to 0.89. From the investigation of carbon variability within the soil profile and by tillage practice, the 0-5 cm depth in a no-till field contained significantly higher levels of carbon than any other locations. Using the selected calibration model with the soil NIR probe data, a soil profile map of estimated carbon was produced, and it was found that estimated carbon values are highly correlated to the lab values. The array of sensors (VIS-NIR, electrical conductivity, insertion force) used in the probe allowed estimating bulk density, and three of the six fields were satisfactory. The VIS-NIR probe also showed the obtained spectra data were well correlated with nitrogen for all fields with RPD scores of 1.84 or better and coefficient of determination (R 2 ) of 0.7 or higher.

A Mobile Sensor Platform for Measurement of Soil pH and Buffering

This paper pertains to a mobile sensor platform (MSP), which simultaneously measures soil pH and electrical conductivity (EC). The device samples soil and presents the sample to an ionselective electrode for pH measurement. This provides a fairly dense coverage of pH readings across the field, but does not assess the buffer pH, which is needed to make a lime recommendation. EC, which is indicative of changes in soil texture and CEC, may be useful for quantifying buffer capacity. Specifically, it is hoped that a combination of pH and EC readings can be used to model buffer pH. Alternatively, a near infrared (NIR) reflectance system is being considered for future versions of the MSP. The NIR measurements relate to organic matter, CEC, clay content, and pH. The addition of NIR may further enhance the ability to assess spatial variations in pH and buffer capacity. This work provides examples of using EC and NIR data to enhance pH and buffer pH estimations on a field scale.