Page 64 - Enzymes in Tropical Soils

52 Enzymes In Tropical Soils

Hendrickson and Doughlass, 1993; Sanz-Cobena et al., 2008). Some urease
inhibitors are Phenylphosphorodiamidate (PPD), Trichloroethylphosphoro-
diamidate (TPD), Diethylphosphoro-triamide (DPT), Sarsaponin (SSO), N-(n-Butyl)
Thiophosphoric Triamide (NBPT), and Hydroquinone (HQ). The effectiveness of
urease inhibitors are determined by soil types, soil water contents, and culture
contitions (Cai et al., 1989). Sanz-Cobena et al. (2008) used NBPT to inhibit the
work of urease in a urea-fertilized soil under mediterranean conditions. They
found that the NH 3 emissions from plots fertilized with urea and treated with NBPT
was lower than those from plots treated with urea alone. The argued that this
phenomenon was associated with a reduction in urease activity during the first 9
days after inhibitor application. The reduction in urease activity also promoted a
+
decrease in the exchangeable NH 4 pool. Some researchers also used slow release
fertilizers to cope with the production of NH 3 (Fan and Li, 2010).
Nitrate ions are the available form of N for plant absorption. However,
nitrate ions may volatilize to the atmosphere through denitrification, particularly
when soils are waterlogged or flooded with low redox potentials (Barlett, 1981;
Holcomb et al., 2011) such as in paddy fields. Water-logging or flooding may cause
-
a reductive condition and, hence, NO 3 is reduced to form N 2 (Oxidation state of N
-
is decreased from +5 in NO 3 to 0 in N 2 ), which may easily enter the atmosphere.
This process occurs in paddy soils when Urea is submerged in waterlogged paddy
fields. Kliewer and Gillian (1995) reported that soil management by raising water
-
table may stimulate denitrification. In this situation, the production of NO 3
decreases and its contamination potential to water environment also decreases.
Its effects on soil acidification also decreases. However, this process may drive N
losses as N 2 and N 2 O through denitrification.

4.7 Analyses of Soil Enzymes

The methods of analyses of soil enzymatic activities are found in several
publications (Tabatabai and Bremner, 1969; Hayano, 1973; Frankenberger and
Johanson,1982; Tabatabai and Fu, 1992; Avidov et al., 1993; Vuorinen, 1993;
Nannipieri et al., 1996; Salam et al., 1998d; Elsgaard et al., 2002; Verchot and
Borelli, 2005; Richers-Haunerland, 2013). Analytical methods for four enzymes are
discussed in this section, i.e. acid and alkaline phosphatases, urease, arylsulfatase,
and -glucosidase. All methods basically follow the methods developed by
Tabatabai and his colleagues (Tabatabai and Bremner, 1969; 1972; Tabatabai,

Abdul Kadir Salam - 2014