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The Chemistry and Fertility of Soils under Tropical Weeds 93

diamidate (TPD), Diethylphosphoro-triamide (DPT), Sarsaponin (SSO), N-(n-Butyl)
Thiophosphoric Triamide (NBPT), and Hydroquinone (HQ). The effectiveness of
urease inhibitors is determined by soil types, soil water contents, and culture
conditions (Cai et al., 1989). Sanz-Cobena et al. (2008) use NBPT to inhibit the work
of urease in a urea-fertilized soil under mediterranean conditions. They find 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 argue 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 promotes a decrease in
+
the exchangeable NH 4 pool. Some researchers also use 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) report 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.
The use of hydrocarbon of organic matters by the living things is a part of a
simple carbon cycle shown in Fig. 6.3. Hydrocarbon is initially produced by the
reaction between carbondioxyde and water molecules during photosynthesis in the
chlorophyls of plant leaves. During this redox reaction, C molecule is reduced with
its oxidation state decreases from +4 in CO 2 (oxidized) to 0 in CH 2 O (reduced) with
the sun energy packed in it; while the oxidation state of O increases from -2 in CO 2
(reduced) to 0 in O 2 (oxidized). The hydrocarbon is finally used by organisms for its
energy by the following reaction called respiration (Eq. 6.6).

CH 2 O + O 2  H 2 O + CO 2 + Energy ....... Eq. 6.6

During the above reaction, a reverse redox reaction changes the CH 2 O to produce
H 2 O and CO 2 . The oxidation state of C increases from 0 in CH 2 O (reduced) to +4 in

Abdul Kadir Salam and Nanik Sriyani – 2019