Evaluation and Modeling of the Impact of Environmentally Friendly
5
Kn = Ko times (the smallest of KnI or Kn2 )
(2)
where Ko = nitrification rate under optimal conditions, KnI = coefficient
representing inhibition of nitrification due to environmental factors such as pH,
moisture, temperature (dimensionless), and Kn2 = coefficient representing
inhibition due to the increase of ammonium concentration in soil.
According to Nedan (1990), the inhibition by ammonium takes the form
(3)
where Al and BI are empirical constants and ~)max is the highest
concentration of ammonium that has ever prevailed in the soil during the
fertilization period.
The use of nitrification inhibitors (Nls) as an effective means to increase NUE
and reduce environmental hazards such as nitrate leaching or denitrification is
well documented (e.g., Amberger 1989; Hagin et al. 1990; Shaviv 1993; Trenkel
1997). Nedan (1990) showed that the effectiveness of Nls can be enhanced by
creating synergism between the effect of high ammonium concentration and Nls
on nitrification. Band application of a nitrogen source amended with Nls (DCD or
N-Serve) induced higher N uptake in wheat grain and reduced nitrate leaching
from pots as compared to bulk mixing (Ned an 1990; Shaviv 1993). Glasscock et
al. (1995) determined the synergistic effect between increased levels of
ammonium and the rate of application of DCD or N-Serve on several soils. The
effects of ammonium concentration and Nls on nitrification in a single microsite
(e.g., nest of fertilizers granules, or supergranule) was simulated by Wang et al.
(1998a), emphasizing also the effects of pH changes in soils due to nitrification.
2.2 Controlled-Release Fertilizers
Controlled-release fertilizers (CRFs), and particularly controlled-release nitrogen
(CRN), offer a very effective way to increase NUE and reduce environmental
pollution caused by fertilization (Hauck 1985; Trenkel1997, Shaviv 2000). Of the
different CRFs used in practice, polymer-coated fertilizers are considered most
efficient from both agronomic and environmental points of view (Shaviv, 2000).
Raban (1994) and Zaidel (1996) investigated the mechanisms of release from
coated fertilizers. Based on these studies, mechanistic models of release were
proposed (e.g., Zaidel 1996; Shaviv et al. 2001). The models make it possible to
predict the release of nutrients into water or soil, based on measurable parameters
of the CRFs (e.g., coating thickness, water and solute permeability through the
coating, and granule radius) and they also account for changes oftemperature.
The release consists of three stages: a lag period, a period of linear release and
finally a period of decaying release, as described below.
5
Kn = Ko times (the smallest of KnI or Kn2 )
(2)
where Ko = nitrification rate under optimal conditions, KnI = coefficient
representing inhibition of nitrification due to environmental factors such as pH,
moisture, temperature (dimensionless), and Kn2 = coefficient representing
inhibition due to the increase of ammonium concentration in soil.
According to Nedan (1990), the inhibition by ammonium takes the form
(3)
where Al and BI are empirical constants and ~)max is the highest
concentration of ammonium that has ever prevailed in the soil during the
fertilization period.
The use of nitrification inhibitors (Nls) as an effective means to increase NUE
and reduce environmental hazards such as nitrate leaching or denitrification is
well documented (e.g., Amberger 1989; Hagin et al. 1990; Shaviv 1993; Trenkel
1997). Nedan (1990) showed that the effectiveness of Nls can be enhanced by
creating synergism between the effect of high ammonium concentration and Nls
on nitrification. Band application of a nitrogen source amended with Nls (DCD or
N-Serve) induced higher N uptake in wheat grain and reduced nitrate leaching
from pots as compared to bulk mixing (Ned an 1990; Shaviv 1993). Glasscock et
al. (1995) determined the synergistic effect between increased levels of
ammonium and the rate of application of DCD or N-Serve on several soils. The
effects of ammonium concentration and Nls on nitrification in a single microsite
(e.g., nest of fertilizers granules, or supergranule) was simulated by Wang et al.
(1998a), emphasizing also the effects of pH changes in soils due to nitrification.
2.2 Controlled-Release Fertilizers
Controlled-release fertilizers (CRFs), and particularly controlled-release nitrogen
(CRN), offer a very effective way to increase NUE and reduce environmental
pollution caused by fertilization (Hauck 1985; Trenkel1997, Shaviv 2000). Of the
different CRFs used in practice, polymer-coated fertilizers are considered most
efficient from both agronomic and environmental points of view (Shaviv, 2000).
Raban (1994) and Zaidel (1996) investigated the mechanisms of release from
coated fertilizers. Based on these studies, mechanistic models of release were
proposed (e.g., Zaidel 1996; Shaviv et al. 2001). The models make it possible to
predict the release of nutrients into water or soil, based on measurable parameters
of the CRFs (e.g., coating thickness, water and solute permeability through the
coating, and granule radius) and they also account for changes oftemperature.
The release consists of three stages: a lag period, a period of linear release and
finally a period of decaying release, as described below.