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| pH is a measure of positive hydrogen ions contained in the soil. These ions are acidic and are neutralized when they react with anions which are alkaline or basic. Positively charged ions form ionic bonds with elements in the soil that will decrease fertilizer availability and increase the availability of more toxic elements like aluminum, iron, manganese, and zinc. Aluminum and iron combine to “lock up” phosphates in the soil when the pH is lower than 5.5. pH indicates acidity or basicity of a soil on a scale of 1 to 14 with 7 being neutral, 1 being acid and 14 being basic. This is a logarithmic scale, which means that a pH of 5 is 10 times more acid than a pH of 6 and 100 times more acidic than a pH of 7. This is what makes soil pH so important. Of course most soils range from a pH of 4 to a pH of 10 with anything more acidic or basic being a laboratory chemical. pH regulates the availability of different plant nutrients as well as the carrying capacity of microorganisms that live in the soil. Most legumes do best in a soil with a pH close to neutral because most nitrogen fixing bacteria are not as active in more acidic soils. Acidic soils also slow down the bacteria that decompose organic matter; which also release nitrogen and other nutrients, as well as releasing acids into the soil. An acid pH of 4 to 5 will increase the availability of toxic elements like aluminum and manganese, while a basic pH of 7 to 8 will reduce the availability of iron, zinc, boron, copper, manganese, and phosphorus while boosting the availability of calcium and molybdenum. Because of this, most plants grow best in a pH of 5.5 to 7 with most doing better between 6 and 7. Lime is used to raise the soil pH and sulfur is used to lower soil pH. Sandy soils require less time to change the pH then clay soils but the lime doesn't last as long in sandy soils due to leaching. High clay soils and soil with high organic content require more lime to change the pH with the lime lasting longer in the soil. For this reason, soils that are loam are best suited for most plant growth. Loam soils are around 40% sand, 20% clay, and 40% silt. Sandy soils often drain to well to provide adequate moisture; while clays are often too dense due to fine particles which inhibit air exchange as well as drainage. The most efficient way to lime is to apply lime annually to maintain the pH; instead of waiting for the pH to drop before adding a lot more lime. This method can be more expensive unless you have the equipment necessary to do this. Areas that haven't been limed in a while often need 2 or 3 tons per acre which would take a long time to affect soil pH if done a little at a time. In this situation it is best to apply the full amount of lime and till it in to the soil. Agricultural lime is the cheapest form of lime but takes 4 to 6 months to start having an effect on pH. Pelletized lime is much more expensive but starts to break down and affect pH immediately. The difference between these two types of lime is their particle size. Agricultural lime is ground limestone with coarse particles and pelletized lime is composed of the finest particles, mixed into slurry with clay to form easily spreadable pellets. Pelletized lime will only last for 2 years do to its fine particle size where agricultural lime will last 3 to 5 years due to its courser particle size. When lime is tilled into the soil the individual particles are surrounded by soil particles. The lime particle starts to react with the positively charged hydrogen ions and neutralizes them. This creates a buffered area around the lime particle and prevents the lime from breaking down further. Soil can not break down more than 3 tons of lime per acre due to this factor. If you need much lime for your pH adjustment it should be tilled into the ground. If left on top it will only affect the top layer of soil and very little will make it down into the root zone. Lime does not translocate in the soil the way fertilizers do, it pretty much stays where it is put. On new food plot installations, I usually spread enough agricultural lime to bring the pH up to the desired level. I then spread pelletized lime to affect the pH immediately; so that the crop can grow well while the agricultural lime is breaking down. Pelletized lime will last a year or two in the soil and agricultural lime will keep breaking down for three to five years. Lime applications are a critical element in providing your crop with adequate nutrients. All the fertilizers in the world will fail to feed your plants if it is all locked up in the soil. The added calcium is also excellent for antler growth as antlers are composed primarily of calcium and phosphorus. |