Ph of soil - Knowledgebase Question

Las Vegas, Ne
Question by wayne_debora
May 22, 2010
I am starting a rasied vegetable garden. Thesoil has a ph of 8.2 and I need to make to more acidic. What would you recommend?

Answer from NGA
May 22, 2010


Alkaline soils in the southwest desert are common so you're not alone! In general, vegetables will grow well in a soil with a pH of 6.5 to 7.0. Amending your soil to make it more acidic will probably take a few years. It might be to your advantage to use some pre packaged top soil in place of at least half of your native soil. If that's not possible, you can lower the pH with combinations of additives and amendments. Compost is the preferred amendment because it not only helps to lower the pH but also helps to break up the clay soil to make it friable and to improve the tilth of the soil.

Initially up to four inches of compost or other organic matter should be worked into the top 8 to 12 inches of soil. In subsequent planting seasons, the application should be repeated at about two inches because the compost will disappear within one
or two seasons. Sawdust, composted oak leaves, wood chips, peat moss, cottonseed meal, and leaf mold can be used to lower the pH if compost is not readily available. The nutrient content of organic compost varies depending on the source so you'll want to feed your veggies rather than depend upon the amendments to provide their nutrition.
Agricultural gypsum (calcium sulfate) contains 15 per cent sulfur, helps to break up and aerate clay soil and is also useful for displacing salts in saline soils. But it also adds calcium which is abundant in our desert soils in the form of calcium carbonate. Elemental sulfur is useful for reducing soil pH, is slow acting but produces longer lasting results. A general rule of thumb is to add 1 lb. of sulfur per 100 sq. ft. for every pH point above 7.5. The best way to adjust pH is gradually, over several seasons. Again, if the soil is excessively alkaline, you may find that you are better off filling your raised bed with topsoil purchased from a nursery.

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