Agriculture Reference
In-Depth Information
sources because of their slow N liberation quality compared to common urea. Comparisons of
granular and finely divided fertilizer when broadcast and mixed with soil also show effects of par-
ticle size on nitrification (Hauck and Stephenson, 1965). The rate of nitrification was reported to
be higher when particle size of a fertilizer was smaller (Pesek et al., 1971). The use of ammonium
sulfate, diammonium phosphate, and monoammonium phosphate applied in an aqueous solution
and in a range of particle sizes (1-4 mm) to a poorly buffered sandy soil, the rate of nitrification was
higher than the smaller particle size (Pesek et al., 1971).
Jantalia et al. (2012) evaluated the NH
3
-N loss from four urea-based N sources (urea, urea ammo-
nium nitrate, superurea, and polymer-coated urea) for 2 years using corn as a test crop. Results of
this study showed that super urea that contains a urea inhibitor had the lowest level of NH
3
-N loss as
compared to the other sources. Analyzed across years, the estimated NH
3
-N losses for the N sources
were in the order: polymer-coated urea = urea ammonium nitrate > urea > superurea. In addition,
these authors also concluded that both years results showed that measurement time may need to be
increased to evaluate NH
3
-N volatilization from polymer-coated urea N sources such as polymer-
coated urea. Wu et al. (2011) reported that ammonium rather than NO
3
-based fertilizers is generally
used in paddy fields or in flooded rice to prevent N loss from microbial denitrification.
2.8.8 p
lant
f
aCtors
Plant factors play a significant role in the loss of N from a soil-plant system. Pesek et al. (1971)
reviewed the literature on the effects of plant factors in N losses of a soil-plant system. It was
concluded by these authors that N loss in the cropped area was 20% and in the fallow area, it was
12% of the amount available in a lysimeters study. Similarly, Stefanson and Greenland (1970) in
Australia found, from periodic sampling of gases over wheat, that amounts of N
2
O and N
2
(cumula-
tive) were consistently greater in the presence of than in the absence of growing plants, over a range
of soil water contents from 50% to 80% of field capacity. The higher N loss in cropped land as
compared to uncropped land may be related to denitrification that preferably occurs in the vicinity
of roots. Apparently, root excretions are vitally concerned as hydrogen donors and in the develop-
ment of anaerobic conditions in the rhizosphere (Pesek et al., 1971). McKenney et al. (1995) also
reported that NO + N
2
O production under many crops (hairy vetch, red clover, annual ryegrass,
reed canarygrass, and corn) was significantly higher as compared to control (without plants) treat-
ment under both without aerobic and with aerobic incubation.
2.9 MANAGEMENT PRACTICES TO REDUCE NITROGEN LOSSES
Over the last few decades, N fertilization had played a significant role in increasing crop yields
worldwide. In the future also, the importance of N in crop production will be indisputable due to
the increasing demand of food, fiber, and energy. However, the energetic cost of N fertilizers is very
high and N fertilization often represents the most expensive energy input in cereal-based cropping
systems (Crews and Peoples, 2004). In addition, N is a highly mobile nutrient in soil-plant systems
and lost easily and contributes to agricultural-related pollution through leaching, volatilization, and
denitrification (Drinkwater et al., 1998; Limaux et al., 1999). Indeed, it has been estimated that,
often, 50% or less of the N fertilizer applied to the soil is recovered by cereals and that this per-
centage decreases as the N fertilizer rate increases (Foulkes et al., 1998; Raun and Johnson, 1999;
Blankenau et al., 2000; Giambalvo et al., 2010).
Fageria (2013) reported that N losses from the soil-plant system not only reduced N fertilizer effi-
ciency but are also responsible for environmental pollution. For example,
NO
3
−
leaching in excess can
contaminate body and ground water that may be a problem for human health. Similarly, the emission
of N
2
O gas into the atmosphere can cause ozone layer destruction. Franzluebbers (2007), Herrero
et al. (2010), and Sainju (2013) reported that N fertilization can increase crop yields, but excessive
application can degrade soil and environmental quality by increasing soil acidification, N leaching,
