Environmental Engineering Reference
In-Depth Information
Percentages of elements present in a typical grass plant are presented
in Table 5.1.
Nitrogen
Unlike other essential plant nutrients, nitrogen is not found in significant
amounts in the rocks and minerals of the earth's crust, but most of the
nitrogen in soil is in organic form and unavailable to plants. Fates of
nitrogen in turf are shown in Fig. 5.1.
Soil organic matter contains about 5% nitrogen and must break down
to release it to the soil. In the tropics, organic nitrogen is continuously
converted to its inorganic forms through the process of
mineralization
.
A large part of the mineralized organic nitrogen undergoes a process
called
nitrification
and is finally converted to the soluble nitrate form
(NO
3
). Besides the nitrates, which originate from mineralization of or-
ganic matter, inorganic nitrates are applied directly during fertilization.
Because they exist in soil solution as negatively charged ions, they are not
held by negatively charged soil colloids and can easily be removed from
the root zone by leaching.
The rate of nitrogen mineralization depends on microbial activity; so
soil moisture, temperature, pH and aeration directly affect the process. In
the tropical climate, substantial amounts of nitrogen are lost before they
can be taken up by roots.
Although they are valuable to the turf, nitrates are considered dan-
gerous water pollutants. In the tropics, if amounts are applied that are too
Table 5.1.
Percentages, by weight, of elements in a typical turf-grass plant.
Element
Percentage of dry weight
Oxygen
44.0
Carbon
44.0
Hydrogen
6.0
Nitrogen
1.5
Silicon
1-2
Potassium
0.90
Phosphorus
0.20
Sulphur
0.15
Calcium
0.25
Magnesium
0.20
Chlorine
0.15
Iron
0.10
Manganese
0.05
Other
0.5-1.5
