# Soil pH

World map with soil pH values. Red = sour. Yellow = neutral. Blue = basic. Black = no data

The term soil pH is a combination of soil and pH . It is a measure of the activity of - protons in the ground water and is due to natural buffering , especially through the dead organic matter influence of the soil. ${\ displaystyle (H ^ {+})}$

## Measurement

Electrometric measurement of the pH value in soil samples using the pH combination electrode

The soil pH is measured in a suspension of soil in a pH-neutral buffer solution of calcium chloride or potassium chloride with a pH meter . Since the H + ions sorbed on the exchangers are displaced by the KCl or CaCl 2 ions, the pH value measured in this way is about 0.3–1.0 units below the pH value measured in aqueous suspensions, however, not all information in the literature has been corrected accordingly.

## Solubility of minerals as a function of soil pH

Availability of nutrients according to soil pH

The table shows the areas of high solubility of various minerals in soil water depending on the soil pH. These areas are susceptible to the (toxic) leaching of the dissolved minerals into the groundwater through rain or irrigation, see nitrate pollution of the groundwater , overfertilization and cation exchange capacity .

Soil erosion on unprotected soil surfaces and in the absence of vegetation , e.g. B. if fields are plowed in good professional practice or left bare for too long , leads to humus loss and sediment removal , d. H. to severely damaging effects. By wind and flowing water (precipitation) fertile soil is loosened and carried by the field, which reduces the buffer and field capacity (water storage capacity ) of the soil. Soil degradation is the result, drought and lack of rain have a negative reinforcing and yield-reducing effect . The following pH values ​​are registered for typical healthy cultivated soils :

• 5.0 to 5.5 with <4% organic matter and <5% clay content
• 5.4 to 6.0 with 5 to 12% clay content
• 6.0 to 6.5 with> 13% clay content

The majority of crops thrive in neutral or slightly acidic soils. Some plants thrive in more acidic soils, such as potatoes and strawberries . Cabbage and other plants thrive in alkaline soils. Acid soil input through precipitation or emissions can be dampened in part by the soil's buffer functions, particularly through humus. Soil that reacts too acidic can be neutralized by liming and adding humus or compost . Soils that are too alkaline can be brought to a neutral pH value by adding humic acid- rich peat , ammonium (e.g. contained in liquid manure ) and litter from conifers. A strongly acidic soil environment is particularly critical, since high concentrations of aluminum can then be dissolved. Very basic soils can suffer from a lack of freely dissolved manganese. In general, an increase in the basic pH value leads to an improvement in the structure .

## Examples

The right table shows the pH ranges of different crops,

Culture Soil pH
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5
Rhododendrons
cotton
blueberries
Strawberries
Seed oats
Kidney bean
potato
Bastard clover
Virginian tobacco
Wine
barley
rice
Soybean
Sweet peas
tomato
Crimson Clover
Garden pumpkin
Citrus fruits
carrot
Vegetable cabbage
cucumber
Corn
Apple
pear
peach
rye
Sorghum
White clover
wheat
Olive tree
spinach
onion
asparagus
alfalfa
Spanish Esparsette
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5

on the left shows a tabular listing of soils according to pH ranges.

pH Examples
<3.0 acid sulphate soils
3.0-4.0 Raised bogs
4.0-5.0 Podsole, moor march
5.0-6.0 Parabraunerden, Knickmarsch
6.0 - 6.5 Brown earths, Kleimarsch
6.5 - 7.0 Black earths
7.0 Kalkmarsch
7.0 - 7.5 calcareous fens
7.5-8.0 Neutral salt soils
8.0-9.0 Alkaline floors
9.0-10.0 Limestone marl
10.0-11.0 Limestone powder

## Individual evidence

1. ^ Arnold Finck , Kiel 1976: Plant nutrition in key words , p. 80, ISBN 3-554-80197-6 .
2. Guidelines for appropriate fertilization (6th edition) online at the Federal Ministry of Agriculture and Forestry , 2006 - p. 13; As of June 17, 2010.
3. Scheffer / Schachtschabel Textbook of Soil Science , 15th edition, 2002, ISBN 3-8274-1324-9 .