Soil test results can be a great tool in your nutrient management program so long as you understand how to interpret the results. 

While the OSU Central Analytical Laboratory does not provide fertilizer recommendations or specific interpretation for our customers we can point you in the right direction. 

It is important to note; different crops have different nutrient demands and different ideal environmental conditions. In order to properly interpret your results be mindful of your crop and your climate and use the appropriate nutrient management guide.

One of the best places to start is the OSU Extension Catalog:  Here you can find nutrient management guides for many crops commonly grown in Oregon. There is also information on establishment, irrigation, and pest management. 

For a very general guide to soil test interpretation you should check out:  Soil Test Interpretation Guide

You may also like these somewhat general fertilize guides: Fertilizing Your Garden: Vegetables, Fruits, and Ornamentals or Nutrient Management for Sustainable Vegetable Cropping systems in Western Oregon


A couple of things to get you started:

pH is a master control of nutrient availability. When your pH is not in the optimal range for your crop, it will not be able to take up specific nutrients regardless of how much is available. Measuring pH is always a good place to start. In order to determine how to adjust your pH you will also need to know about the buffering capacity of the soil. We use the Sikora buffer pH test to estimate the lime needed to raise your soil pH. In other extension programs, they have shown a very good correlation between Sikora and SMP buffer results. OSU is working on validating these results for our local soils. Pulblications are also underway to assess the buffering capacity relationship to use sulfur to lower the pH. 

Total Carbon is not a "soil nutrient," however, more C means more organic matter, and more feed for your microbial herd underfoot. This leads to a higher rate of nutrient cycling and supply to the plants, increased soil aggregate stability, increased water holding capacity, a greater buffering capacity, and increased resilience. It is good for the health of your agro-ecosystem. You can calculate your total organic matter by multiplying the total C by two. C*2=OM 

Nitrogen is often the most rate-limiting nutrient in crop production and so is the most economically advantageous to measure to ensure proper fertilizer application. An accurate estimation of the N that will transform from soil organic nitrogen to plant available nitrogen in one growing season has been the goal of many extension faculty and ag professionals who are trying to save their customers money while maximizing yield and minimizing environmental pollution.  You can find some of the work done by OSU extension here:  Nitrogen is complicated in that there are many different foms of N in the soil and the interpretation of each form is dependent on the timing of the sampling, and crop. It is best to talk to an Extension Faculty to fine tune your N applications. 

Phosphorus has the ability to hold tightly to other elements and is often present in unavailable forms. The Bray soil P test is specifically designed and indexed to asses the plant available Phosphates in soils with a low to neutral pH (<7.3) whereas the Olsen soil P test is designed and indexed to assess available Phosphate in soils with an alkaline pH (>7.3). The OSU extension publications have used these tests to assess P needs in crops for a long time. These tests are available at OSU but unless they are specifically requested, we use the Mehlich 3 extraction which can be used to assess many other nutrients, measure organic forms of P, and be useful over a range of pH values. There are good correlations between Mehlich 3 and Bray at low pH and Mehlich 3 and Olsen at a higher pH. However, these do not have a 1:1 relationship. You can not interpret Mehlich 3 results the same way you would Bray or Olsen. Many labs are moving toward Mehlich 3 and you need to be careful with interpretion. Publications are available through a google search but we have more work to do at OSU.

More information on interpretation of the soil health parameters will be coming shortly.