Monday, November 13, 2006

Innovative instrumentation for in-situ soil NO3- measurements.

Atac Tuli, Jan Hopmans, Benjamin D. Shaw, and Jing-Bin Wei. UC Davis, Dept. of Land, Air and Water Resources, Davis, CA 95616

Among the soil nutrients for plant growth, nitrogen (N) is one of the essential macronutrients for crop production, mostly taken up by plants in the form of nitrate (NO3-). The absence of in-situ instrumentation limits the ability to monitor concentration levels of soil solution nitrate and the evaluation of plant nutrient uptake mechanism for specific environmental and agricultural management practices. Two new in situ measurement techniques are presented that can potentially be applied in the field, with measurements recorded electronically in real time as opposed to extracting soil solutions for laboratory measurements. Both use a stainless steel solution sampler design. The first technique uses the adoption of a NO3- ion selective electrode (ISE) to determine in-situ NO3- concentrations in soil solution. Current laboratory tests confirmed that using a one-point calibration procedure, the NO3- ion selective electrode can measure in situ NO3- concentrations in soil solution. The second technique measures NO3- concentration using ultraviolet absorption spectroscopy. This sampler has internal optics that enable a beam of light to be directed through the solution in the sampler. The internal optics are coupled to optical fibers that allow light to be transmitted into and out of the system, enabling analysis with a portable fiber optic spectrometer.  This paper describes the evaluation of both innovative measurement approaches for their potential use with in-situ measurements.

Handout (.pdf format, 484.0 kb)