Environmental Engineering Reference
In-Depth Information
Buffering
Large change
Small change
Fig. 3.8. When an equal volume of water is added to each tank, the level in the slim
tank will rise significantly, but that in the wide one will rise only slightly. Similarly,
addition of the same amount of lime may drastically change the pH of low-CEC soil
and have only a small effect on the pH of high-CEC soil.
required to adjust the pH of sands, loams and clays to levels suitable for
turf-grass.
Effect of Soil pH on Nutrient Availability
Nutrient availability is greatly influenced by soil pH (Fig. 3.9). Correct
pH is especially important for phosphorus availability, which is greatest
in neutral soils. In acidic soils, phosphate ions bond with iron and
aluminium to form insoluble iron and aluminium phosphates. At pH
levels above 7.0, insoluble calcium and magnesium phosphates are
formed. Phosphorus solubility, and hence availability to plants, is great-
est at a soil pH between 6.0 and 7.5. Soil pH strongly affects availability of
Table 3.2. Approximate quantities of ground CaCO
3
(kg/100 m
2
) required to raise
pH to 6.5 in a 15-cm-thick root zone.
Original soil pH
Sand and loamy sand
Loam
Clay loam and clay
5.5
7-15
20-40
40-50
4.5
15-25
40-70
80-100
