A key to producing abundant crops is the quality of the soil in which they are grown. Soils lacking the proper nutrient content will yield fewer crops of lower nutritional value than crops grown in good soil.
Poor soil can be enhanced by the application of fertilizer, but the nutrient content of the soil must be known in advance so that the proper type and amount of fertilizer can be added.
When determining the elemental content of soils, both sample preparation and analysis must be considered. Sample preparation generally involves subjecting the soil samples to acid at elevated temperatures so that the elements of interest are extracted into the acid. This can be accomplished in two ways: open vessel or closed vessel.
Open vessel sample preparation involves heating the soil at sub-boiling temperatures for up to four hours and then separating the acid from the soil through filtration or centrifugation. The advantage of open vessel extraction is that a large number of samples can be prepared at the same time, but the disadvantages include having to separate the soil from the acid, the loss of volatile elements or elements in volatile forms, and possible incomplete extraction of the elements of interest.