Increasing Capacity for Soil Minerals

Our sandy soil has very low organic matter, just barely 2%, and even below that in some fields!  A healthy soil has at least 5% organic matter, so our soil needs a lot of TLC.  My previous blog posts have been all about soil minerals like calcium and sulfur.  However, we’re running into a bit of a problem adding more of these minerals because our soil’s cation exchange capacity (CEC) is so low.  CEC is a measure of a soil’s ability to hold nutrients and exchange them with plants (cations are positively charged elements, like calcium).  Tiny clay soil particles and organic matter contain the sites that are negatively charged and can attract and hold cations in a positive/negative bond much like how opposite magnet poles attract.  So, soils with high clay content and/or high organic matter have a high CEC and therefore will hold lots of nutrients and make them available to plants.  With our very sandy, low clay, and very low organic matter soil on the farm, we have a soil that can’t hold many nutrients right now.

Soil Test Results, click to enlarge

If you look at our soil test, our major nutrients (calcium, magnesium, potassium, sodium) are sort of well balanced in base saturation.  Calcium is within the 60%-70% range, magnesium is over 20%, but not too bad, and potassium and sodium are in the right ranges.  However, we need more of these nutrients to make great pasture that will sustain the health and growth of our future animals.  For example, the best pastures have at least 3,000 lbs of calcium per acre available to plants.  Our best field has 1,400 lbs per acre available, so we are far short.

We want to add calcium to our soil, but with such a low capacity to hold nutrients, will the calcium just leach out?  On the flip side, does our soil actually contain lots of minerals, but they’re just not available to plants because our CEC is so low?  I really wish we knew the answers to these questions!

We can increase organic matter by rotationally grazing animals or by shallow-tilling cover crops as green manure.  Rotationally grazing animals seems to be the speediest option, but we don’t have animals yet.  Shallow-tilling green manure would cost a lot in heavy farm equipment, and I’m not in love with tillage, especially with super-light soil that can blow away very easily.

We have chosen one path forward that we’re excited about.  It’s carbonized lime from Fertilizer Brokerage! This is high-calcium lime pelletized with humates and other goodies.  Humates are organic matter that has decayed as much as possible. It’s deep, dark carbon and great for the soil.  We’re hoping the humates will stimulate soil life and increase organic matter, and the added calcium will help us start approaching the ideal 3,000 lbs per acre that we need.  We’re going to add about 200 lbs per acre of carbonized to our pastures this spring, and again in the fall.  We’ll have to be patient and wait and see what happens.

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