Simultaneous field measurement of nitrate-nitrogen and matric pressure head
1993
Moutonnet, P. | Pagenel, J.F. | Fardeau, J.C.
Groundwater protection from NO3 pollution requires frequent measurements of potential water fluxes and NO(3)-N concentrations. This study was conducted to improve researchers' abilities in managing these two parameters by using a new device. We developed a method allowing the researcher to simultaneously measure the hydraulic head and the NO(3)-N concentration in the soil water solution. Measurements were made using the tensionic, in which a permeable porous ceramic cup allows the diffusion of NO3 from the soil to the water inside the cup. Diffusion is completed within 8 d. A system of capillary tubes allows this water to be extracted for measurement of NO(3)-N, and it may be reinjected subsequently. An aliquot can be used for isotopic analysis. Tests carried out on a maize crop (Zea mays L.) in 1991 led to two conclusions: (i) on a 200-m-long transect of 50 tensionics (placed at 4-m intervals and at a depth of 50 cm), statistical analysis made on the first three of the successive series showed the consistency of measurements with an 18% mean coefficient of variation (CV) for NO(-3), whereas the mean CV for hydraulic head was 14%; (ii) in a battery formation (four probes located at depths ranging from 40 to 130 cm, with four sampling repetitions), the tensionics allowed easy monitoring of the distributions of hydraulic head and NO(3)-N within the horizons of the soil profile.
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