I have to place samplers at different depths (to 1.2 m), for sampling soil water, and I have to be sure, that tillage will not destroy them.
In my research, I always placed the top one at 30-cm depth. In this case, the tillage depth was about 23-25 cm.
typical water bottle sampler consists of a cylindrical tube with stoppers at each end, and a closing device that is activated from the surface. Multiple water samplers can be attached sequentially to a vertical hydrowire for sampling at multiple depths on a single cast, or they can be mounted on a rosette frame (often in conjunction with an in situ sensor array) which allows for collection of replicate samples at the same depth.All members of the sampling team should avoid touching the stoppers and the insides of the sampler.
My assumption is that you are interested with leaching rates of N compounds from a particular farm. In such a case, both sampling procedure and land topology are very important factors to consider. It is also important to note that column water tends to give a better analytical result than leached water as soil will filter off nutrients. My point is, column sampling will give a better understanding of leaching rate than underground sampling unless you were interested in ground water contamination rates.
It depends on the "soil water" you need to sample. Assuming that you want to examine the N-compounds in the gravitational water flowing from the soil profile to the ground water, the tubes are OK. If you are interested in the N-compounds available for plants and different kind of crops, you have to use tension samplers.To use this kind of samplers, it's better to insert them at about 80-100 cm far from the plants; you need also a small fense around (again about 100 cm) to protect the sampling procedure.
If you want to sample soil water that has a matric potential less than -50 kPa use a porous ceramic cup. If the soil water has a matric potential between - 50 and 0 kPa use a porous stainless steel cup.
It all depends on what component of the soil-water you want to sample. It is good to sample both the N-leaching component that leaves the plant root zone using passive samplers (e.g. Wetting Front Detectors, see www.fullstop.com.au) and the resident N component using active lysimeters (Suction cups).
place your sampler at 120 cm depth from soil surface that will give best idea of N compounds .
We use P80 ceramic tension lysimeters ( for soil solution studies). Be careful to avoy ceramic tension probes for water studies: the ceramic composition is different and you could get troubles for elements release.
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