SOIL pH, What is it?

SOIL pH, What is it? Most gardening book at some point will refer to soil pH. So what is it and why is it important? Soil pH is a measurement of free hydrogen ions which determine if a soil is acid or alkaline. A pH of 7.0 is neither or is considered neutral. Areas of the world with limited rainfall like Eddy County NM typically have alkaline soils; areas with high rainfall have acid soils. Unless a person has really worked at amending their soil or imported soil from high rainfall area, the soil in Eddy County will have a soil pH of 7.4 to 8.3. Soils with a pH of 7.5 and higher have high calcium carbonate content (caliche) as free lime. Some of Eddy County soil is 13% calcium carbonate. A quick test is place some acid like vinegar on the soil, if there is free lime it will bubble. Carlsbad Caverns is made of limestone so we should expect a lot of free lime in our soils. In general pH of greater than 8.3 will not support plant life except for some specifically adapted species. Soil from 7.5 to 8.3 pH micro nutrients become unavailable to plants most common is Iron. With a pH of 6.0-7.5 most plants will grow and is the pH that most garden book recommends. Just as there are a few alkali loving plants there are some acid loving plants as well, these include blueberries, azaleas, strawberry, that is why they are difficult to grow in Eddy County. When the pH is lower than 6.8- to 5.5 lime is add to the soil to increase the pH. We do not need to add lime to our soil in Eddy County, our pH is much to high already. Soil pH is important chemical property because it affects the availability of nutrients to plants and activity of soil microorganisms. Iron chlorosis is common in the west and Eddy County due to the alkaline soils. As the pH increases phosphorous, zinc and manganese become less available to most plants. Soils which are moderately in high pH that is above 7.3 to 7.7 or so can be managed by giving extra attention to increasing the organic matter, using organic mulches. Plants are less tolerant of dry soil conditions when the pH is high. Soil with a pH of 7.3 and above have so much free lime that soil cannot be amended for acid plants. Home soil test kits are not reliable in Eddy County alkaline soils, unless they are for specifically alkaline soil. I have had a number of sales people tell me they work, I supply them a sample from my small place which I have laboratory data on and none come close to being accurate. The majority of the market is in high rainfall areas and acid soils. Most cannot read our high pH and will indicate an extremely acid soil and give very bad advice for our soil. One company is sending me one for alkali soil so I will let you know how it tests out. I have had two people, one farmer and one gardener who worked diligently for more than 50 years on their soil, and they had wonderful soil, good tilth, smell and texture. They passed away and their replacements did not keep up the intensive management, within 4 years that soil had reverted back to what it was to start with. If your soil bubbles in vinegar your soil has excess free lime and it cannot effectively lower the pH because it has to high of a buffering capacity. Texas A&M at the El Paso Experiment Station added over 40 tons of sulfuric acid to the soil and changed to pH two tenth for three days then it reverted back to what they started with. This said the soil will benefit from the application of elemental sulfur and the use of sulfate fertilizers. With almost 40 years’ experience as County Agriculture Agent my personal thought are do whatever you can to add organic matter to your soils, use sulfate based fertilizers, supplement micro nutrients in chelated form, and NEVER add lime to our soil. Subscribe to Eddy County Ag news at: http://nmsueddyag.blogspot.com/ Eddy County Extension Service, New Mexico State University is an equal opportunity/affirmative action employer and educator. All programs are available to everyone regardless of race, color, religion, sex, age, handicap, or national origin. New Mexico State University, U.S. Department of Agriculture, and the Eddy County Government Cooperating.