13
Each plant needs elements in different quantities and this is the reason why each plant requires
a particular range of pH to optimize its growth.
For example, iron, copper and manganese are not soluble in an alkaline environment. This means
that plants needing these elements should theoretically be in an acidic type of soil. Nitrogen,
phosphorus, potassium and sulfur, on the other hand, are readily available in a pH range close
to neutrality.
Abnormal pH values may increase the concentration of toxic elements for plants. For example,
a plant may not tolerate an excess of aluminum ions that may increase under acidic conditions.
When pH values are too far from neutral conditions a less permeable and more compact soil
may result.
Soil Management Strategy with regard to pH
• It is advisable to choose crops that are suitable for the soils pH range (e.g. rice, potato,
strawberry crops have a preference for acid soil).
• Add fertilizers that do not increase acidity (urea, calcium nitrate, ammonium nitrate and
superphosphate) or lower alkalinity (ammonium sulfate).
• A cost evaluation should be made prior to soil pH modification to determine cost of soil
ameliorants versus value of plants grown.
• pH modification may produce critical improvement in plant performance but may take too
long or be short lived.
For example, by adding lime, the effects in clay soil can last for as long as 10 years, but only
2‑3 years in a sandy soil.
For an acid soil, we can use substances such as lime, dolomitic, limestone and marl, according
to the nature of the soil. See
Table 1.
Soil Ameliorants Clay soil
Silty soil
Sandy soil
CaO
30‑50
20‑30
10‑20
Ca(OH)
2
39‑66
26‑39
13‑26
CaMg(CO
3
)
2
49‑82
33‑49
16‑33
CaCO
3
54‑90
36‑54
18‑36
Table 1.
Quantity (q/ha) of pure compound necessary to increase 1 unit of pH.
SOIL pH
