Does anyone know the procedure of using centrifuge to measure the soil field capacity? I am looking for a alternative method that will not use pressure plate.
You will find some references in the literature by simply searching on-line. But why this method when pressure membrane/plate methods are so well established? Keep in mind also that contemporary agronomy prefers to work with drained upper limits rather than any laboratory determination. I can send a method for this if you wish.
In references of both papers you can find more references.
I think the centrifuge method would have great advanate, when compared to porous plate, that it requires much less time. It is not needed to wait various weeks for the results.
Article Validity of the Centrifuge Method for Determining the Water ...
I think Omar Cruz has given to you the procedure to get what you are looking for. Just one thing to remember is that it is better you have the retention curve utilizing standard procedures that you may find in the web. Out of this curve you may find any water content to a given pressure and vice versa
The soil-water capacity should be, preferentially, determined directly in the field by measuring soil-water content after the internal soil drainage substantially ceases upon gravity forces. The measured soil-water content at this point can be associated with the corresponding soil-water matric potential. Thus, if the soil-water retention is known, as determined by the centrifuge method, for example, then one can extract from the retention curve the value of field water-capacity. For the conditions of tropical soils, such the ones found in the central part of Brazil, we have determined that the field-water capacity corresponds to values of matric-potential ranging from 8 to 12 kPa.
Before you use any method of field capacity measurement, you should before try to define the field capacity value for the soils that you are working. It is important to remember that field capacity is different for different soil textures and depends on its structure. There is no a fixed value for the field capacity. Sometimes soil scientists utilize -6, -10 or -33 kPa, but it is better to evaluate the value for your soil. Regarding papers about the method, try to see the article entitled "Validity of the centrifuge method for determining the water retention properties of tropical soils" by Reatto et al. (2008), SSSAJ, (72) 1547-1553. You can also find several papers by searching on internet.