"If you want to use soil test results to develop a fertilizer program, use a different extraction method"
- Is water (or a saturated paste extractant, or mixing irrigation water with soil) a good way to look at soil nutrients?
- What about two tests to look at "available" and "exchangeable" nutrients, is it good to look at both?
The quick answer to both of those questions is no.
The saturated paste extraction is used for measuring soil salinity (ECe).
I think water extractions, whether with a saturated paste, one part soil with two parts water (1:2 extraction), or one part soil with five parts water (1:5 extraction), are quite interesting and informative for research purposes. But water extraction results are not useful as a decision making tool in turfgrass maintenance.
Carrow et al. wrote about this in Clarifying soil testing: 1. Saturated paste and dilute extractants. They explained that the "saturated paste extraction is not the best method for determining soil fertility levels and can be very misleading."
I wrote about this in Water-based Extraction Methods for Turf Soils. At the time I wrote that article, I was a graduate student, doing lots of research about extraction methods, and I appreciated water as an extractant a bit more then than I do now. It is great for research into soil nutrients. But "it is not possible to take the numbers and decide that they are low enough to justify fertilizer applications ... If you want to use soil test results to develop a fertilizer program, use a different extraction method."