Agriculture Reference
In-Depth Information
The use of chemical fertilizers is fundamental to improve crop yields and maintain sustainability
of the cropping systems. From 1960 to 1990, the use of N fertilizer in modern agricultural systems
has increased in parts of Asia, North America, and West Europe. This was accompanied by a
steady increase in the yield of most annual crops (Food and Agricultural Organization of the United
Nations, 2000). On the other hand, negative impacts of N compounds on the atmosphere, ground-
water, and other components of the ecosystems have also been reported (Socolow, 1999; Presterl
et al., 2003). For example, excessive N fertilization in intensive agricultural areas of China results in
serious environmental problems such as eutrophication (Li et al., 2010), greenhouse gas emissions
(Xue et al., 2012), and soil acidification (Guo et al., 2010). Galloway et al. (2004) estimated that out
of 268 Mt per year of reactive N (all N compounds except N
2
) added every year to continents and
inland water, of which 100 Mt was coming from manufactured fertilizers, 48 Mt was lost as nitrate,
53 Mt as ammonia, 46 Mt as nitrogen oxides, and 11 Mt as nitrous oxide. Improving N recovery
by crops is one of the options identified by Galloway et al. (2004) to reduce the amount of reactive
N in the environment (Heffer and Prudhomme, 2013). Currently, improving N management and
development-related policies are major issues in crop production and environmental protection in
China (Xue et al., 2012) and other countries (Fageria, 2013). Looking into this scenario, appropriate
management of this nutrient is necessary not only to improve the yield but also to reduce environ-
mental pollution.
Overall, nitrogen use efficiency is a function of the capacity of the soil to supply adequate levels
of N, and ability of plants to absorb, transport in roots and shoots, and to remobilize to other parts of
the plant (Baligar et al., 2001). Plant interaction with environmental factors such as solar radiation,
rainfall, and temperature, and their response to diseases, insects and allelopathy, and root microbes
have a greater influence on nitrogen use efficiency in plants. Optimizing N use efficiency is an
imperative from agronomic, economic, and environmental perspectives. The nutrient use efficiency
in crops can be increased by adopting various agronomic practices as well as by understanding
the molecular nature of relevant traits and using this knowledge in breeding programs (Malik and
Rengel, 2013). Significant progress has been made both agronomically and at the molecular level
toward characterizing nutrient use efficiency. Some examples of this success are supplying nutrients
to match the crop demand (Wiesler, 1998), crop rotation (Raun and Johnson, 1999), and preci-
sion agriculture (Wong et al., 2005), which can be adopted for improving nitrogen use efficiency.
Nitrogen-efficient genotypes of several crop species have been identified (Fageria et al., 2008, 2011;
Rengel and Damon, 2008). Genetic variability in root growth among crop species and genotypes
within species has been identified (Fageria and Moreira, 2011; Fageria, 2013, 2014). There is evi-
dence in the literature that some plant species and genotypes within species have a capacity to
grow and yield well on soils low in available nutrients (Rengel and Marschner, 2005; Brennan and
Bolland, 2007; Damon and Rengel, 2007; Malik and Rengel, 2013). The objective of this chapter is
to discuss the latest development in nitrogen management in crop production and suggest measures
to improve N use efficiency in crop plants.
8.2 SOIL MANAGEMENT PRACTICES
Efficient agricultural production and management practices are required to meet the growing
demand for food without compromising the environment and agricultural resources (Heumesser
et al., 2013). In this context, adopting adequate soil management practices is essential to improve
the nitrogen use efficiency in crop plants. These management practices may include improvement in
the physical, chemical, and biological properties of the soil. Improvement in the physical, chemical,
and biological properties of the soil creates favorable conditions for the plant growth, including root
system, which can absorb more nutrients and water and utilize N more efficiently. Some physical
properties can be improved by proper land preparation during the sowing of a particular crop. If a
soil is compacted, it is better to have deep ploughing to break the hard pan and incorporate plant
residues into the soil.
