l am about to carry out a pot experiment and l need to know the appropriate way to collect leachate, its storage temperature and duration and the appropriate leachate sampling interval/period. l need your views. Thanks.
This publication might help: Standard Methods for the Examination of Water and Wastewater. If you are measuring anything biological 4C is usually the best temperature. Additionally hold times will again depend on what you are measuring in the leachate.
Regarding the storage temperature depends on the analysis you need to perform: for example if you have to determine the nitrate concentration, is better to freeze the sample and than defrost it immediately before carry out the analysis.
If you put plastic trays under each treatment (previously disinfected with sodium hypochlorite and washing with water) will be enough. Pick the leachate after filtered and keep it in erlenmeyer and in refrigerator until analysis. But try to do it in the next 24 hours after collecting.
It depend on the parameter you are looking for as the table attached for
Recommended sample container, preservation and holding time
You can directly collect the percolates by locating plastic dishes under the pots and storing them frozen at -20 ºC for physic-chemical measurements or at -80 ºC for biochemical measuments. A very accurate way for obtaining leachates is by the rhizon samplers. Check the web site: http://www.rhizosphere.com/
To collect the gravitational water / leacheates you can put the experimental pot inside another one leaving a space between them to storage your liquid sample, be careful to collect periodically this one in order to avoid the evaporation, contamination, algae growth...and other problems. Also, you can connect the hole that there is in the bottom of the pot with a sampling bottle by using a tube (you can add a filter on the top of the bottle to avoid the entrance of soil particles, etc). Finally, you can use a syringe connected with the pot by a tube (with or without filter) if you want to force the leacheate extraction (it is difficult to obtain a leacheate in a maize pot experiment).
Once you have obtained the leacheate samples, it depends on the parameters to be measured,the way of storage them. If you are going to perform microbiological test, the Tª has to be below 4ºC to stop the biological activity. For physic-chemical analysis the temperature varies between -80ºC; -20ºC up to room-temperature depending of the parameter to be measured.
Finally, check the water needs for maize plants, soil to be tested (texture, nutrients, etc...if you are going to use sieved soil, natural one, mixed with perlite...) and the experimental design to accomplish the objectives of the study.
In principle, pot experiments are not suitable for studying leaching of nutrients. Leachate will leave the pot only when there is saturation of soil in the pot and saturation is harmful to maize. Thus you cannot find the truth which you are seeking.
I agree with Bijay Singh. The physiological optimum of maize is far from field capacity (or maximum water retention of soil in the case of pots). So, rhizon samplers or ceramic cup lysimeters can be used at no saturation moisture levels.
I guess the leachate in pot experiment do not ocurs only the soil is soil saturated condition. The water fluxes in soil still occurs in unsaturated conditions. What do not happens in unsaturatd conditions is the preferential fluxes in open holes (from surface to botton) and macropores. The unsaturated hydraulic conductivity can reduce in a large magnituted from saturated conditions to near saturated ... The question is also related to irrigation rates that you will apply in your pots. Theoretical simulation of water and some chemical elements can be done if some parameters are available.
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