Hi Oscar you wrote "weighing lysimeter are appropriated for water balance studies". This is not true because you modify the soil water gradient at the base of the lysimeter compared to the surrounding natural soil. But if lysimeters have been already set up you could manage them with manual clipping to change the leaf transpirating area. 

Dear Serge, thanks for your feedback.

Well, according to the technical advance of the lysimeters supplied by UGT, the lysimeter includes a porous ceramic bars installed at the bottom, which connect the capillary system of the soil with a pressure regulated water reservoir. The pressure in the reservoir can be adjusted according to the current tension at the surrounding soil measured by a tensiometer. This way it is possible to transfer the tension from the surrounding soil to the bottom of the lysimeter. Additionally, the temperature is directly transferred from the soil to the lysimeter bottom using a heat exchanger. Using insulated lysimeter vessels the controlled lower boundary conditions lead to a natural tension and temperature gradient in the lysimeter. Then, lysimeter approach makes it possible with minimum soil disturbances.

Hi Oscar Pérez-Priego; Though I have not worked on  weighing type lysimeter under grazing but have experience that animal grazing disturb the lysimeter alignment and data. Hence they should be fenced and grasses may be cut and feeded to animals. Thanks

O pisoteio dos animais vai trazer ruido aos dados do sistema. A opção de corte da forragem é bastante interessante.

I suggest you do a search on google scholar, as there have been quite a few studies done in Australia and New Zealand that I know of.  I found 9750 papers for the search string lysimeter grassland in google scholar.  Refine the search and you should have more than enough.

Dear Freeman,

Thanks for your suggestion. I bet that only few of the 9750 papers are under such specific management conditions. Whenever there are, they  use lysimeter for nutrient leaching analysis and not refer to weighing lysimeter. I will further refine the search as you suggest.

If you are using lysimeters to estimate ET in a particular grassland with cattle-grazing, artificial soil compaction could be done along with manual clipping, if soil-compaction from cattle hooves happens to a large degree. As soil compaction can change water balance, by decreasing infiltration and increasing runoff. 

Hi Saha,

That's a good point. If the alternative of manual clipping is taken, the diameter of the lysimeter (1m) allow to make it without stepping on it. On the other hand, what is interesting is to know the degree of compaction in the site and its effect among water balance components. Should be it more negligible in a sandy soil texture ?

Thanks for the comment!!

Hi Oscar, yes, in general, sandy soils would have less compaction, good point ! I wonder though about the organic matter in soils; a large organic horizon could also be subject to some degree of compaction that slows down infiltration. Some quick lab studies of soils taken from the site and subjected to varying degrees of compaction and then having water poured on them, to measure infiltration rate could give some idea.

We published a paper on the effects of trampling on surface runoff in an alpine grassland with quite sandy soil some time ago, which might be interesting for you (Leitinger, G., E. Tasser, C. Newesely, N. Obojes & U. Tappeiner (2010) Seasonal dynamics of surface runoff in mountain grassland ecosystems differing in land use. Journal of Hydrology, 385, 95-104.)

Concerning the simulation of trampling, a Swiss colleague got some sheep hoofs and fixed them on her shoes to simulate trampling. To apply realistic pressure on the soil you probably have to step on the lysimeter, and accept a disturbance of the measurements for a certain time period. just make sure that the balance is not damaged by the additional weight.

Thanks Nikolaus for the paper.

It seems interesting..