Edith on Soil Amendments

by Edith Isidoro-Mills -- Spring is almost here and soon gardeners will be thinking about preparing their soil for spring planting.  Be careful what soil amending and fertilizing recommendations you follow.  Some practices could actually defeat the benefits of any fertilizer you use. Recently I was reading a nationally distributed magazine online touting the benefits of adding lime.  At one time lime was recommended for curing all soil problems.  Indeed, many people on the East Coast where soils tend to be acidic were seeing tremendous benefits from this practice but those farmers and gardeners in the arid West were not benefiting.  The problem with this recommendation and the article I was reading was they both failed to take into account soil pH and the affect lime has on it. The nutrients plants need exist in the soil either as free ions available for uptake by plant roots or bound to soil particles and unavailable for absorption into plant roots.  The availability of these nutrients is affected by soil pH with the best balance of nutrients being available at a soil pH of between 6 and 7.5.   The addition of lime increases soil pH and is beneficial if your soil's pH is less than 6.0 but if your soil is high then these essential plant nutrients become bound tightly to soil particles and are unavailable for uptake into the roots.  Even if you add these nutrients through applications of fertilizer. they will become quickly bound to soil particles unless the pH is changed. Most soils in the arid West are high in pH and this is generally true of any region with low rainfall.  The answer to soil problems for gardeners whose soil pH is above 7.5 is the addition of a combination of gypsum, organic matter in the form of compose, and the use of good quality water.  However, before assuming this is true of your soil it should be tested for pH and many garden centers will sell a soil testing kit for determining your soil's pH.  If you are willing to spend more money you can send a sample of you soil to a soil testing laboratory for a more thorough test and usually a set of recommendations. Both lime and gypsum have calcium and adding calcium to the soil isn't necessarily bad except the ions each of these compounds is associated with changes the way calcium interacts with water and other components of the soil.  Lime tends to increase hydroxyl ions in the soil thus raising the pH of the soil.  Gypsum does the opposite thus lowering soil pH. Improving the pH balance of the soil alone will not insure good plant nutrition and workable soil.  Both lime and gypsum are mineral amendments and contribute no buffering ability to the soil.  Soil pH may be corrected by the addition of either, depending on the soil's condition but it won't stay corrected for long if it doesn't have some buffering capacity.  One of the many roles of organic matter in the soil is it increases soil buffering capacity by adding more sites where ions can bind.  It also may slightly lower pH.  Unfortunately soils in arid regions are low in organic matter.  Compost is one way to add organic matter.  The application of manure is another way but not just any manure.  Only manure from herbivores is used and it should be thoroughly composted.  Three reasons for thoroughly composting manure are killing bacteria that may cause human disease such as E. coli, killing weed seeds that could sprout plants that compete for plant nutrition, and reducing the salt content of the manure. So, before you decide to amend your garden soil make sure you know its condition and amend it to free up the most nutrition for your plants.         Read more local news at The Fallon Post home page