Organic Gardening and More

Soil Testing -- All Gardening is Local

Calvin F. Bey                   CFBey1936@cox.net

Question:   I am ready to plant my potatoes, tomatoes, etc.  What fertilizers should I use?  

Answer:  That standard question applies to all gardens, and I can really only answer the question if I have a soil test report.  Backyard vegetable gardens are extremely variable, so without soil test results, I would be guessing.  All gardening is local.  Guessing at what to apply may work or it may not.   If you want to see your garden producing nutrient-dense vegetables, you will need more precise calculations.   

With your AR Soil Analysis Report in hand, I can give you recommendations with much more assurance of success.  Yet, because uptake of nutrients is so complex, even the best advice is not always going to be spot-on.    

Question:  So just what are the factors that go into making fertilizer recommendations? 

Answer:  First, know what nutrients already exist in the soil  The AR soil test will provide that information.  I like the Mehlich 3 soil test that AR uses.  It shows pounds of nutrient per acre for 11 different nutrients.   That is very helpful.

A second factor is the Estimated Base Saturation for Calcium, Magnesium, Potassium, and Sodium. This is a ratio of the major cations in the soil, and it important to to see those percentages in a certain ratio i.e. roughly 68:12:4:2.

The third factor is the soil Cation Exchange Capacity.  This is a measure of how well the soil holds on to minerals.  A low number suggests a sandy soil, and a high number suggests a soil with clay and/or a soil with lots of organic matter.   Soils with low CECs, will need smaller does of fertilizers, but more frequent applications.  Soils with high CECs can use higher amounts of certain fertilizers.  

Fourth, it is good to see a Calcium to Magnesium ratio of about 7:1.  It should be higher in clay-like soils and lower in sandy soils.  Calcium loosens soils and Magnesium causes soil to compact. 

Fifth, I will look at the pH, but mostly as a monitor of how well the first four factors are satisfied.  A deeper understanding of these and other concepts can lead to production of nutrient-dense vegetables.  I provide  the details in my classes and now have an app that helps in making calulations.