Understanding the Saturated Paste (Water-Soluble) Soil Test
Providing another layer of insight into your soil.
Soil testing methods are selected based on the questions being asked and the management system in place. The saturated paste soil test, also known as a water-soluble soil analysis, is designed to evaluate nutrients and salts that are readily available in the soil solution at the time of sampling. Rather than estimating nutrient reserves, this test provides a direct snapshot of what is dissolved in soil water and immediately mobile.
Background and Intended Use
The saturated paste test was originally developed by the U.S. Soil Salinity Laboratory in Riverside, California, with a primary purpose of assessing soil salinity and sodium-related concerns. Early applications focused on determining whether irrigation water could negatively affect soil structure, particularly through measurements such as Sodium Adsorption Ratio (SAR).
Today, Brookside Labs uses this same water-soluble extraction approach across a range of systems. It is used routinely in the sports turf industry, where fertigation is common and nutrients are supplied in soluble forms. In agricultural settings, the test is most often applied in orchards, vineyards, and row crop fields where manure is applied regularly or where performance issues arise that are not evident in standard chemical soil analyses.
How the Saturated Paste / Water-Soluble Test Is Performed
Unlike traditional soil tests, saturated paste samples are not dried or ground prior to analysis. When samples arrive at Brookside Labs, they are immediately processed.
Soil is mixed with deionized water, or the client’s irrigation water, until it reaches a saturated, paste-like consistency. The mixture is allowed to rest overnight so soluble components can equilibrate. The following day, vacuum filtration separates the soil solution from the solid material. The extracted solution is then analyzed for nutrients, soluble salts, chloride, bicarbonates, and pH.
This process measures what is present in the soil solution itself, not what is held on soil exchange sites.
What the Test Measures
The saturated paste (water-soluble) soil test measures nutrients that are dissolved in soil water and immediately available for movement and uptake. Because the soil solution is dynamic, concentrations can change rapidly in response to irrigation, rainfall, fertigation, manure application, or biological activity.
Results from this test are typically lower than values reported from standard exchangeable nutrient analyses. This is expected, as the two methods measure different pools within the soil system. Water-soluble nutrient data does not directly correlate with traditional fertility soil tests and should be viewed as a separate perspective on soil behavior.
When the Saturated Paste / Water-Soluble Test Is Applied
It is frequently applied in areas with salt or sodium concerns, soils with low exchange capacity, and management systems where nutrients are applied in readily soluble forms. In row crop production, it is often used when observed issues do not align with standard soil test results or when manure is a consistent part of the nutrient management strategy.
A Snapshot of Soil Solution Chemistry
The saturated paste (water-soluble) soil test offers a moment-in-time look at soil solution chemistry. Rather than describing the soil’s long-term nutrient-holding capacity, it captures what is present, mobile, and soluble at the time of sampling.
At Brookside Labs, all saturated paste samples undergo quality control review prior to reporting. When used alongside standard soil analyses, this test provides an additional layer of insight into soil conditions that may not otherwise be visible through traditional testing methods alone.
For more information, contact your local Amplify Consultant or reach out to Brookside Labs at (419) 977-2766 or at info@blinc.com.
Heather Rindler, CCA
Research Agronomist
Brookside Labs | Amplify Network









