In situ monitoring of soil solution nitrate in saturated and unsaturated sandy soil

A lack of in-situ instrumentation limits continuous monitoring of soil solution concentration to evaluate environmental (contaminants) and agricultural management (plant nutrients) practices. We developed a prototype soil solution monitoring technique, to measure long-term in-situ nitrate concentration, consisting of an in-situ stainless-steel porous cup, with real time concentration measurements using a UV fiber-optic sensor and Ion Selective Electrode (ISE). The measurement technique does not require soil solution extraction, but is based on insitu soil solution equilibration by diffusion between the porous cup and the surrounding medium. The technique is presented for nitrate solution with sandy soil using new designed of solution samplers. Analytical solutions are presented to evaluate solute diffusion coefficients, as controlled by a variety of soil water contents. The principles of operation are demonstrated for diffusion a saturated and unsaturated Oso Flaco Sand, illustrating the potential application solution samplers in a soil environment

Comparison of air and water permeability between disturbed and undisturbed soils. Soil Sci

ABSTRACT flow and transport very difficult. This lack of knowledge on the control of pore geometry on flow and transport Although soil structure and pore geometry characteristics largely has led to incidental microscopic studies that investicontrol flow and transport processes in soils, there is a general lack of experiments that study the effects of soil structure and pore-space gated flow and transport coefficients as a function of characteristics on air and water permeability. Our objective was to geometric soil pore-space properties (e.g., nitions in literature, Clennell (1997) presented a comThis is so because of the inherent complexity and heteroprehensive review of the tortuosity concept for a range geneity of soils, thereby making a physical interpretaof different flow and transport processes in porous metion of the accounting of pore-space characteristics to dia. Although strictly a microscopic concept, pore tortuosity is applied macroscopically with pore structure an

Analytical Modeling of Soil Solution Monitoring by Diffusion in Porous Cups

There is increasing interest toward in situ solution monitoring of soil chemicals for agricultural, industrial, and ecological purposes. Rather than extracting soil solution, a series of laboratory experiments was conducted to evaluate a diffusion equilibration technique, providing for real time in situ soil solution nitrate concentration via UV absorption spectroscopy. Experiments allowed for diffusion of nitrate from an outside reservoir into a porous cup. The experimental data were compared with model predictions using three different analytical solutions: (i) an exact solution (EX model) assuming radial symmetry that includes a porous cup with a porous wall and a finite size outside reservoir, (ii) an approximate solution (RC model) that assumes an infinitely large supply reservoir with a porous cup wall that does not influence ion diffusion, and (iii) and a model based on an electric circuit analog (ECA model). The results indicate that the ECA solution provides the best match overall to the experimental data