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pH

농사 : 2012.12.29 17:35



* http://sanibelseaschool.org/classroom/ph

Here are some common substances and their pH levels:

1.8 – 2 lime juice

2.4- 3.4 vinegar

2.9- 3.3 apple juice

3.5- 4.5 grapes

5.2 acid rain

5.7 normal rain

6.5 – 8 drinking water

7.35 – 7.45 human blood

7.36 – 8.21 sea water

8.4 baking soda

11.5 household ammonia

12.5 household bleach


* http://www.docstoc.com/docs/53010826/pH-scale

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* http://www.simplehydro420.com/wp-content/uploads/NuteLockoutChart.jpg

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* http://www.420magazine.com/forums/problems-pests-disease-control/157773-multiple-problems-flowering-plants-help.html

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* http://boards.cannabis.com/indoor-growing/202962-nute-lockout.html

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* http://www.oakleafgardening.com/how-to/understand-your-soil/soil-ph/

Soil pH

The pH of a soil is an expression of the concentration (or, more precisely, the activity) of hydrogen (H+) ions in the soil. The higher concentration of hydrogen ions, the more acid the soil. The hydrogen ions can be counterbalanced by ‘base’ ions such as calcium, magnesium and potassium; the higher the concentration of these ions, the more alkaline the soil is.

Generally speaking soils tend to become more acidic over time. This is due to rainfall (which is slightly acidic), microbes in the soil releasing hydrogen ions as they respire and crops taking up nutrients (in particular the base ions which counterbalance acidity) and then being harvested, so the nutrients aren’t returned to the soil. The extent to which a soil is affected by these changes depends on the type of soil. Soils which have a lot of clay or humus in them tend to have a higher ‘buffering capacity’, which means that they can balance out changes in pH by holding onto some ions and releasing others, eg buffering increased acidity by holding onto hydrogen ions and releasing calcium ions. This means that sandy or silty soils tend to be more susceptible to pH changes, particularly increasing acidity.

Understanding the acidity of your soil is important for several reasons:

  • Different nutrients become unavailable to the plants or reach toxic levels at particular levels of pH. For example, very acid soil can cause phosphorous to be unavailable and aluminium to become toxic. Very alkaline soil can reduce the availablility of iron or cause toxic levels of boron.
  • Soil organism activity (which is critical for breaking down organic matter and making nutrients available to plants) can be suppressed by extreme levels of pH. This is good if, for example, you have acidic soil because you should avoid clubroot (which perfers alkaline conditions) but not so good because you’ll also have far less earthworm activity to break down organic matter and aerate your soil.
  • Plants have differing tolerances to acid/alkaline soils. Plants prefering more acidic (or ‘ericaceous’) soil include rhododendrons, ericas (heathers) and blueberries. Alkaline soils are preferred by plants such as celery, daffodils and lettuce.

pH is measured on a logarithmic scale (so one unit change represents a ten-fold change, two unit changes a hundred-fold change, and so on) from 0 to 14. Soil pH generally only ranges from 3 to 9 (though most are between 5.5 and 7.5). This is an illustration of the pH scale with some common substances indicated:

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* http://climatechange.wikispaces.com/pH+Scale

The pH Scale expresses the acidity or basicity of a substance. The scale usually ranges from 0-14, but a pH under 0 and over 14 is possible and is known as off the charts. A pH of 7 is neutral, which is neither acidic nor basic. Each increment is 10 times as acidic or basic as the next, meaning the pH scale is logarithmic.

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Rainfall is currently becoming more and more acidic because carbon dioxide in the air dissolves into water, creating dilute acids.
Acidic precipitation has a very low pH, like 4 or maybe as low as 3. The increased amount of acid rain is in response to the increased release of sulfur dioxide and nitrogen oxide from the burning of fossil fuels.

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Not only is rainfall becoming more acidic, the ocean is becoming more acidic too due to the increased amounts of carbon dioxide in the atmosphere. The chemical Bromothyml blue is an indicator of pH and carbon dioxide levels. The Bromothyml blue did indicate the increased carbon dioxide in the ocean. The acceptable pH range for ocean water is between 6 and 11, but 11 is over doing it.
* http://www.extension.org/pages/65269/soil-ph-in-vineyards


Soil pH in Vineyards

Last Updated: Septem

ber 25, 2012

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Impact of soil pH on nutrient availability.

What is pH?

Soil pH is a measure of acidity or alkalinity [the activity of hydrogen (H) ions in the soil solution].  The pH scale is numbered from 0 to 14, with value of 7 being neutral. pH values less than 7 reflect acidity, whereas numbers above 7 indicate alkaline conditions. The pH scale is logarithmic (pH = –log H); a pH of 5.0 is ten times more acidic than a pH of 6.0 and one hundred times more acidic than a pH of 7.0. 

Soil pH, which can range from 3 to 10, is affected by many factors, including the parent material, the amount of organic matter, the degree of soil leaching by precipitation, and additions of lime or acidifying fertilizers. While soil pH can be precisely quantified, qualitative terms are often used to describe soil pH based on grapevine performance. From a viticultural standpoint, “strongly acidic” soil will generally be a pH of 5.5 or lower and may exhibit mineral-nutrient imbalances.  “Slightly acidic” (with a pH of 5.6–6.9) and neutral (with a pH of 7.0) vineyard soils generally have better nutrient balance for plant growth. Calcareous soils—those that contain free calcium carbonate—may be “slightly to strongly alkaline”, with soil pH greater than 7.0 or greater than 8.5, respectively. Vineyard soils with a pH greater than 7.5 are rare in eastern North America but will typically exhibit nutrient imbalances where they do exist.

pH and CEC

Soil pH, cation exchange capacity (CEC), and base saturation values are used together to determine a lime recommendation (the amount of calcium carbonate equivalent needed to raise the soil pH by a desired amount).  First, CEC is directly related to soil’s buffer capacity. It takes more lime to raise a soil pH from 4.5 to 6.0 in a soil with high CEC (that is, a clayey soil with a high percentage of organic matter) than it does in a soil with low CEC (that is, a sandy soil with a low percentage of organic matter). Second, there is a positive correlation between soil pH and base saturation, but the relationship is not linear. The chemistry of aluminum and carbonate buffer the soil at low and high pH, respectively. Therefore, it takes more lime to change the pH of soils containing aluminum or carbonate than it does to change the soil pH where aluminum and carbonate are not factors.

Effects of pH on nutrients

Aside from improving the percent base saturation, there are other good reasons to maintain soil pH at optimal levels. In strongly acidic soils, high amounts of free aluminum and iron precipitatephosphorus (P) out of the soil solution, making P unavailable to the plant. Aluminum toxicity can also affect root growth by inhibiting cell division in the root apical meristem. In addition, soil microorganisms, which improve soil fertility through the breakdown of organic matter and metabolism of nitrogen, can be inhibited in acidic soils.

The availability of micronutrients (for example, zinc, ironmanganese, and copper) also changes with soil pH. In general, availability is high in acidic soils and low in alkaline soils.  High availability at low soil pH can cause direct toxicity symptoms on the vine or cause indirect deficiency of another element. For example, high availability of zinc and iron may limit phosphorus availability for root uptake. In contrast, low availability of zinc and iron at high soil pH can lead to zinc or iron deficiency. Zinc deficiency is common in California vineyards with sandy, high pH soils. Some grape varieties are susceptible to iron deficiency in vineyards where the soil is alkaline, cool, and wet.

* http://t2.gstatic.com/images?q=tbn:ANd9GcRGWZ1f_5HLHYAWR1SycNEalGAjHEGvK00OSM67BcmmDAZlr55bbunV2mi3VA

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* http://thegoodwitch.ca/how-to-balance-your-ph-levels/

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