What Does My Soil Test Say?

Apr 02, 2019

Maybe your fields are finally dry enough to plant , or maybe they are still underwater. Whichever scenario you are in , you are probably wondering how the weather this spring has affected your soil. The best way to find out what is in your soil is by soil sampling , and more specifically , by grid soil sampling. Why? 

A grid soil sample provides valuable information to help you place the right amount of nutrients in the right place on the right field. The result is a smart fertility decision , and making smart decisions means more money in your pocket at the end of the season. Whether you are starting a fertility program on new land or wanting to know how much nitrogen or sulfur your field lost due to rain in the off-season , soil sampling will provide a baseline for the field and help you set realistic goals for this year’s harvest.

So where do you begin? Evaluate your soil analysis sheet. There’s a lot of information on one page , so let’s start with the basics!

pH , Nutrients , and Ratios
When reading a soil analysis , pH should be the starting point. Most field crops have an optimal pH range of 5.5-6.5 where nutrient uptake is optimized. If your pH is lower than 5.5 , it may be time to spread lime. This is when you should look at the soil pH and the buffer pH to figure out lime requirements. After pH , the nutrients will be listed. The results are usually listed in parts per million or lbs. per acre and can be used to make a recommendation based on crop planted and your 2019 yield goals. As a general rule , if the results are listed in ppm , you can multiply ppm by two to get pounds per acre.  

Once you’ve reviewed the individual nutrient needs , the next step is to take a look at the nutrient ratios. If one nutrient level gets too high in the soil it could affect the uptake of other nutrients. Consider this scenario: In parts of the Mississippi Delta , high magnesium levels are found in the soil which are antagonistic for potassium uptake. In this case , extra potash may be needed to help keep a proper balance. This balance is why a soil test may show adequate levels of a nutrient in the soil , but the same nutrient in a plant tissue sample is deficient. The Mulder’s Chart shows how nutrients affect each other antagonistically or synergistically.
Cation Exchange Capacity 
Now what about the line that says Calculated Cation Exchange Capacity? A soil analysis also shows cation exchange capacity , often referred to as CECs. CECs are important when making fertilizer applications , chemical application rates , and—with organic matter—can give an understanding of water holding capacity.

A cation is a positively charged ion. Common cations in soil include hydrogen , aluminum , iron , calcium , magnesium , potassium , zinc , ammonium and sodium.  A soil’s CEC is the ability of that soil to hold and attract cations. The higher the CEC , the more cations a soil will hold. High clay content and organic matter cause CECs to increase over their sandier soil/low organic matter counterparts as there are more exchange sites or more places a cation can bind on soil colloids. Though it may be the smallest section of a soil analysis , CECs play a major role in determining soil pH , and the timing and rates of fertilizer and residual herbicides.  

Are you ready to know what’s in your soil? Contact your local GreenPoint AG for your soil sampling needs , and we will provide a variable rate prescription through Incompass®.

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