Environmental Engineering Reference
In-Depth Information
Acidic
Neutral
Alkaline
4
5
6
7
8
9
10
Nitrogen
Phosphorus
Potassium
Sulphur
Calcium
Magnesium
Iron
Manganese
Boron
Copper and Zinc
Fig. 3.9. Availability of essential nutrients depends strongly on soil pH (bar thickness
corresponds to relative availability of the nutrient). (Drawing by R. Castro.)
other nutrients as well. In general, the availability of nitrogen, potassium,
calcium and magnesium is high in neutral soil and decreases rapidly
when pH drops below 6.0 or rises above 8.0. Iron, manganese, boron and
several others are most available when soil pH is in the acidic range. As
the pH of soil approaches the otherwise optimal 7.0, their availability
decreases, and deficiencies can become a problem. Turf-grasses in the
tropics often suffer from iron deficiency, especially on alkaline, coral soils
along the coast or on sodic (sodium-rich) soils in arid climates. Some-
times only foliar applications of iron and other micronutrients is effective.
Because the balance between soil pH and nutrient availability can be so
fine, soil acidity should be tested periodically and maintained within the
optimum range.
The Soil Water
Most of the water in soil originates from natural precipitation, irrigation
or (occasional) flooding and is held in the pore space between the solid
particles of minerals and organic matter. After an intense rain or exces-
sive irrigation, the soil is saturated; all the pores are filled up. With time,
