Acid or Alkaline? What pH means in gardenspeak

I found this resource that explains about acidity of soil.



http://www.plantea.com/pH.htm





Acid or Alkaline? What pH means in gardenspeak


By Marion Owen, Fearless Weeder for PlanTea, Inc. and Co-author of Chicken Soup for the Gardener's Soul

Did you know that beer, Swiss cheese and soil are all related?

That's right. They are kissing cousins. The pH of things is one of the mysteries of daily life. It comes up when the conversation turns to beer making, swimming pool water, dairy products or garden soil. This degree of acidity or alkalinity, is expressed as a number is called pH. What's really being measured is the concentration of hydrogen (H) ions -- the more hydrogen ions there are, the more acid the thing being measured is.

If it sounds like a foreign language, don't worry. Fortunately, a clever scientist developed the pH scale. It runs from 0 to 14, where neutral is right in the middle at 7.0. Less than 7.0 is acidic (sour) and more is alkaline (sweet). Lemon juice, for example, has a low pH of 2.0 while baking soda measures a high 8.5. Take a look at the scale below to see pH values for common items:





How the pH scale worksLike the Richter scale that's used to rate earthquakes, the pH scale is not linear. The intervals between numbers is logarithmic, which means every number on the scale shows ten times less H concentration than the number below. Soil with a 5 is ten times more acidic than soil with a pH of 6.

What pH means to you, the gardener

Did you get all that? Don't worry. Let's take a look at pH from a practical gardening standpoint. Remember, below 7 is acidic; above 7 is alkaline. The good news is that most home garden plants prefer soil that's a little on the acidic side, around 6.5. Exceptions include potatoes and rhododendrons, which thrive in 5 or 5.5, and many desert plants that grow well in soil having a pH of up to 8.0. (See chart below). Thankfully, plants are usually pretty forgiving and will be happy as long as the reading is close. But some plants do have more specific requirements.

Why is pH is so important in gardening? Because soil acidity or alkalinity directly affects plant growth. If a soil is too sour or too sweet, plants cannot take up nutrients like nitrogen (N), phosphorus (P) and potassium (K). And plants need specific amounts of those compounds--just like we need proteins, carbohydrates and vitamins to grow--to thrive and fight off disease and stress. Let's look at it another way...

Nutrient uptake and pH

Have you ever been disappointed with the performance of your vegetables or flowers, even though you gave them the best care you could? Truth is, pH might have been the problem. Plant roots absorb minerals such as nitrogen and iron only when they are dissolved in water. Now if this soil "soup" solution (the mixture of water and nutrients in the soil) is too acid or alkaline, some nutrients won't be dissolved, and as a result, they are unavailable to plants. They are said to be "locked up."

To put it another way, if the pH isn’t close to what these plants require, some nutrients, such as phosphorus, calcium and magnesium, can’t be dissolved in water. And since plants drink their food instead of eating it, if the nutrients aren’t dissolved first, the plant can’t absorb them. Thus, your corn, lettuce, roses and geraniums won't grow or produce to their full potential.

Most nutrients that plants need are readily available when the pH of the soil solution ranges from 6.0 to 7.5.
Below a pH of 6.0 (acid): Some nutrients such as nitrogen, phosphorus, and potassium are less available.
Above a pH of 7.5 (very alkaline): Iron, manganese, and phosphorus are less available.


Why soil pH varies so much

I wish I could snap my fingers and tell you that if you live in a certain area of the country you have a specific pH. But soil pH can vary from one side of the street to the other. What's more, we also learned that different plants require different pH levels.

Many environmental factors, including amount of rainfall, vegetation type and temperature can affect soil pH. Here are some general guidelines:
Areas with heavy rainfall and forest cover have moderately acid soils.
Soil in regions with light rainfall and prairie cover tend to be near neutral.
Areas of drought and desert conditions tend to have alkaline soils.

The pH of cultivated and developed soils often differ from that of native soil. During construction, for example, the topsoil may be removed and replaced by a different type. Hence, your garden soil pH could be very different from your neighbor's.
Having said all this, please don't get fixated over perfect pH and dump a bunch of lime in your garden to sweeten the soil. Let's take it step by step...

How to correct pH in soil

As the saying goes, "To know where you are going, you first have to know where you are." Thus, when changing the pH of soil, the first thing you need to do is test your soil. Test it at home using a do-it-yourself kit or with a portable soil probe/pH meter. You can also send a sample to a lab for a more in-depth analysis. Sending your sample away to a private lab will give you the most complete analysis, although it's more expensive than sending it to your local extension service.

"The soil is not, as many suppose, a dead, inert substance. It is very much
alive and dynamic. " -- J.I. Rodale, "Pay Dirt" (1898-1971)

Soil can be brought back into balance fairly quickly if they are not too far out of the ideal pH range of 6.5 to 7.0. You can make adjustments by applying soil amendments such as dolomite limestone or gypsum. The best way to make pH adjustments is to incorporate compost and mulch. There are dozens of materials that you can compost. Adding organic matter to the soil also tends to make both acid and alkaline soils more neutral. On the other hand, applying chemical fertilizers makes soil more acidic.

To RAISE the soil pH(Translation: If you have acidic soil)

If your soil is too acid, you need to add alkaline material. The most common "liming" material is ground limestone. Ground limestone breaks down slowly, but it does not burn plants like "quick lime" does. Apply it to the garden and lawn in the fall to allow time for it to act on soil pH before the next growing season. A rule of thumb for slightly acid soils: apply 5 pounds of lime per 100 square feet (say a 5 x 20-foot raised bed) to raise the pH by one point.

Apply limestone: 5 pounds per 100 square feet

Applying wood ashes also will raise soil pH. Wood ashes contain up to 70 percent calcium carbonate, as well as potassium, phosphorus, and many trace elements. Because it is powdery, wood ash is a fast-acting liming material. Be careful, a little goes a long way. Limit your application to 2 pounds per 100 square feet and only apply it every other year in a particular area.


To LOWER the soil pH(Translation: If your soil is too alkaline)

In this case, you need to add a source of acid. Options include pine needles, shredded leaves, sulfur, sawdust and peat moss. Pine needles are a good source of acid and mulch. Peat moss with a pH of 3.0 is often recommended as a soil additive. Before you use it though, consider the other options, because peat moss is nutrient-poor, expensive, and it's a nonrenewable resource.
So the next time you jump in a pool or sip on a glass of wine, you can relax, knowing that all things are connected -- many of them by pH!!!

The Myth of Phosphate Fertilizer (EXT)

I extracted this article from http://www.puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Phosphate.pdf

This is useful resource to explain the impact of excess Phosphate in soil.


Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor,
Puyallup Research and Extension Center, Washington State University


The Myth of Phosphate Fertilizer:

"Phosphate fertilizers will stimulate root growth of transplanted trees and shrubs"
This commonly spread myth originates from the legitimate addition of phosphorus to agricultural fields.

Phosphorus is one of the inorganic macronutrients needed by all plants for the manufacture of phosphatecontaining nucleic acids, ATP and membrane lipids. Soils that have been heavily used for agricultural crops are often deficient in phosphorus, as are acid sandy and granitic soils. In landscaped urban soils, however, phosphorus is rarely deficient and the misapplication of this element can have serious repercussions on the plant, the soil environment, and adjoining watersheds.

When an element is limiting in the soil, plant growth slows. This phenomenon is called environmental dormancy. When the deficient element is added, the environmental constraint is lifted and plant growth resumes at the normal rate if nothing else is limiting. Somehow the observation of growth restoration was interpreted as growth stimulation (i.e. a growth rate greater than normal) and hence fertilizers are often regarded as miraculous compounds (just look at the names of some of them!).


One of the classic symptoms of phosphorus deficiency is reddening of the leaves. Unfortunately, many environmental stresses also induce foliar reddening; examples include cold temperature, high light intensity, insect damage, and drought. Urban landscape plants are much more likely to experience one of these stresses than phosphate deficiency.


In contrast to phosphorus, nitrogen is much more likely to be limiting in urban landscapes. Nitrogen deficiency is characterized by overall leaf chlorosis. Among other things, the lack of nitrogen reduces the plant's ability to take up phosphorus. When nitrogen is restored to optimal levels, the plant's ability to scavenge phosphorus from the soil is markedly improved. It's important to realize that when nitrogen is deficient it does not logically follow that other nutrients must be deficient as well.


Because nitrogen is so often deficient in an actively growing landscape, the addition of ammonium nitrate usually restores shoot growth. Phosphate addition, on the other hand, often has no apparent effect (probably because it's generally not limiting in perennial landscapes. This observation has led landscapers and fertilizer manufacturers to claim that phosphorus stimulates root growth (there is no shoot growth, ergo it must be stimulating root growth). The unfortunate result of these assumptions is the mantra "nitrogen for shoots and phosphorus for roots." While there are no nitrogen toxicity symptoms per se, the same cannot be said for phosphate toxicity.

The result of phosphate overfertilizing is leaf chlorosis. Phosphorus is known to compete with iron and manganese uptake by roots, and deficiencies of these two metal micronutrients causes interveinal yellowing. It's my belief that many of the chlorotic shrubs we see in urban landscapes are suffering indirect iron (or manganese) deficiency from overapplication of phosphorus. Moreover, it has been experimentally demonstrated that high levels of phosphorus are detrimental to mycorrhizal health and lower the rate of mycorrhizal infection of root systems. This mutually beneficial relationship between the fungus and the plant roots allows the plant to more effectively explore the soil environment and extract needed nutrients. In the absence of mycorrhizae, the plant must expend more energy growing additional roots and root hairs to accomplish the same task.


In addition to harming beneficial soil organisms, excess phosphate will eventually find its way into waterways. Unlike urban landscapes, aquatic plants are most often limited by phosphate and the addition of phosphate will induce algal blooms (eutrophication). Such blooms are always followed by increased bacterial activity, resulting in lowered oxygen levels and the eventual death of fish and other animals. As green industry professionals, it is incumbent upon us to recognize that excessive use of phosphorus in landscapes is a resource-wasteful, ecosystem-damaging practice.


Bottom line:

• Maintain organic material (mulch) on landscapes; this provides a slow release of phosphorus and other needed macro- and micronutrients over time.

• Don't use phosphate fertilizer when transplanting; in most cases ammonium nitrate fertilizer is
adequate.

• If you have a nutrient deficiency that is not relieved by nitrogen addition, try a foliar application of likely nutrients and see if the symptoms are alleviated. This prevents excessive addition of mineral nutrients to the soil.

For more information, please visit Dr. Chalker-Scott’s web page at http://www.theinformedgardener.com.