Environmental Engineering Reference
In-Depth Information
Losses to the
atmosphere as
N
2
, N
2
O
Losses to the
atmosphere as
NH
3
Losses of N with
removed grass
clippings
Denitrification
NH
4
+
NO
3
−
Soil organic N
Ammonification
Nitrification
Leaching
Fig. 5.1. Fate of nitrogen in turf.
large for the plants to absorb immediately, heavy monsoon rainfalls can
leach them from the soil into the ground water. Techniques designed to
minimize this process are use of slow-release fertilizers and 'spoon-
feeding', the frequent (weekly) application of small amounts of fertilizer
rather than infrequent applications of larger amounts.
In addition to leaching, nitrogen can be lost from the soil in gaseous
form. Organic matter and, to an even larger extent, urea and other
fertilizers containing ammonia (NH
4
) undergo the process called
ammo-
nification
. Ammonium ions valuable for plants become converted to
ammonia gas (NH
3
) and lost to the atmosphere. In the rainy season,
when turf remains flooded for long periods, nitrate fertilizers may be
lost through a process called
denitrification
. Under anaerobic conditions,
where oxygen is limited, nitrate ions can be biologically reduced to
nitrous oxide (N
2
O) or nitrogen gas (N
2
) and lost to the atmosphere.
For economic and environmental reasons, therefore, nitrogen applica-
tions must be managed carefully.
Phosphorus
Phosphorus forms insoluble compounds with aluminium and iron at low
soil pH and with calcium at high soil pH. Even in neutral soil, phos-
phorus is almost always combined with other elements. Insoluble com-
