4
A. Shaviv
The control over nitrate formation and release in soils can be achieved in three
main ways: (1) by applying ammonium-rich sources in nests, bands, or supergranules (microsites), which create high local concentrations of ammonium and
thus reduce the rate of nitrification (Darrah et aI., 1987; Shaviv, 1988); (2) by
using nitrification inhibitors - NIs (Amberger 1989; Trenkel 1997), particularly in
combination with high local concentrations of ammonium or in supergranules
(Yadvinder-Singh and Beauchamp 1987; Glasscock et al. 1995); and 3) by using
controlled-release nitrogen (eRN) fertilizers (Hauck 1985; Trenkel 1997; Shaviv
2000).
The presentation focuses on laboratory, pot, and lysimeter experiments,
demonstrating the above-mentioned effects. This is followed by a sensitivity
analysis done using N dynamics models that describe the behavior of N in a
single microsite (e.g., nest, band, and supergranule) and in soil profile.
2 Experiments with Environmentally Friendly
Fertilization Techniques
2.1 Inhibition of Nitrification - Experimental Work
Incubation studies of Shaviv (1988) and Nedan (1990) and results of a lysimeter
experiment (Shaviv 1988) showed very significant decreases in nitrification rates
as ammonium concentration in soils was, locally, increased. The results confirmed
earlier findings (e.g., Malhi and Nyborg 1985; Darrah et al. 1987). In theses
studies the reduction of nitrification rate was associated with the high local
ammonium or ammonia concentration in the soil. In some cases the nitrification
can be further reduced due to the reduction of pH, owing to proton formation
during the oxidation of ammonium (Darrah et al. 1987; Nedan 1990). From a
practical point of view the inhibition conditions can be created by application of
the ammonium source in a band, nest, or supergranule.
Based on experimental work (Shaviv 1988; Nedan 1990) a nitrification model
that accounts for the inhibition due to the increase of ammonium concentration in
soil was proposed (see also in Wang et al. 1998a):
(1)
where (N03) = concentrations of the nitrate obtained by ammonium oxidation
in soil, in mgN kg'l,
Wang et al. 1998a), and Kn = rate constant of nitrate formation, which takes the
form:
A. Shaviv
The control over nitrate formation and release in soils can be achieved in three
main ways: (1) by applying ammonium-rich sources in nests, bands, or supergranules (microsites), which create high local concentrations of ammonium and
thus reduce the rate of nitrification (Darrah et aI., 1987; Shaviv, 1988); (2) by
using nitrification inhibitors - NIs (Amberger 1989; Trenkel 1997), particularly in
combination with high local concentrations of ammonium or in supergranules
(Yadvinder-Singh and Beauchamp 1987; Glasscock et al. 1995); and 3) by using
controlled-release nitrogen (eRN) fertilizers (Hauck 1985; Trenkel 1997; Shaviv
2000).
The presentation focuses on laboratory, pot, and lysimeter experiments,
demonstrating the above-mentioned effects. This is followed by a sensitivity
analysis done using N dynamics models that describe the behavior of N in a
single microsite (e.g., nest, band, and supergranule) and in soil profile.
2 Experiments with Environmentally Friendly
Fertilization Techniques
2.1 Inhibition of Nitrification - Experimental Work
Incubation studies of Shaviv (1988) and Nedan (1990) and results of a lysimeter
experiment (Shaviv 1988) showed very significant decreases in nitrification rates
as ammonium concentration in soils was, locally, increased. The results confirmed
earlier findings (e.g., Malhi and Nyborg 1985; Darrah et al. 1987). In theses
studies the reduction of nitrification rate was associated with the high local
ammonium or ammonia concentration in the soil. In some cases the nitrification
can be further reduced due to the reduction of pH, owing to proton formation
during the oxidation of ammonium (Darrah et al. 1987; Nedan 1990). From a
practical point of view the inhibition conditions can be created by application of
the ammonium source in a band, nest, or supergranule.
Based on experimental work (Shaviv 1988; Nedan 1990) a nitrification model
that accounts for the inhibition due to the increase of ammonium concentration in
soil was proposed (see also in Wang et al. 1998a):
(1)
where (N03) = concentrations of the nitrate obtained by ammonium oxidation
in soil, in mgN kg'l,
Wang et al. 1998a), and Kn = rate constant of nitrate formation, which takes the
form: