Agriculture Reference
In-Depth Information
Nitrogen uptake from the soil-plant system and its translocation from root to shoot and grain are
important physiological and biochemical processes in plants which are associated with N use effi-
ciency. These processes can be better understood through a molecular approach or studies. Nitrogen
translocation processes in plants are controlled by transport proteins (Malik and Rengel, 2013).
The identification and characterization of transport systems that direct the flow of N metabolites
between cellular compartments, in tissues and organs, and throughout the plants is therefore crucial
for N distribution and improving N use efficiency in crop plants (Malik and Rengel, 2013). Key
enzymes (two enzymes involved in the conversion of ammonium into amino acids in plants, that
is, glutamine synthetase, GS, and glutamate synthase, GOGAT) and genes for N use efficiency
have been identified (Hirel and Lea 2011; Malik and Rengel, 2013). Transgenic rice lines showed
an increase in N use efficiency relative to control rice (Shrawat et al., 2008). A comparative study
between the control plants and transgenic rice at the transcriptome level revealed that distinct func-
tional classes of genes were differentially expressed in roots and shoots. However, none of the N
uptake and assimilatory genes was upregulated or down-regulated (Beatty et al., 2009).
The rapid adoption of transgenic insect-protected corn hybrids has occurred during the past 15
years in North and South America (Traxler, 2006). For example, the benefits of hybrids with trans-
genic protection against Western corn rootworm (
Diabrotica virgifera virgifera
) include improved
consistency of insect control, healthier root systems, advancements in environmental and farmer
safety, and increased yields (Bender et al., 2013). These transgenic hybrids result in significantly
less root damage and stunting (Vaughn et al., 2005), which in turn may allow them to accumulate
more water and mineral nutrients compared to their nontransgenic isolines (Bender et al., 2013).
8.7 CONCLUSIONS
Nitrogen nutrition has been considered as one of the most important factors in increasing crop
productivity in the last half of the twentieth century. It is one of the nutrients required by plants
in large amounts and is also quite expensive. In addition, N recovery efficiency in crop plants is
lower than 50%. Hence, a large amount of N is lost in the soil-plant system. This not only increases
the cost of production but also creates environmental pollution. Under these situations, adopting
appropriate nitrogen management practices in crop production is essential to increase crop yields
and to reduce the cost of production. Further, adequate use of N also maintains sustainability of the
cropping systems and also reduces environmental pollution. Improving the soil physical, chemical,
and biological properties can improve the crop yields and N use efficiency. Crop responses to N and
N use efficiency are very similar for similar types of crops in the tropics and temperate climates.
Further, the same factors influence efficiency. Hence, greater efficiency of N use is obtained when N
is placed in a band rather than broadcast, when N is applied to the plant in the right amount near the
seeding time, and when N availability is in synchrony with N requirements by the crop. Ammonium
sulfate has proven to be superior to upland and lowland rice compared to urea. This may be related
to the tolerance of rice to soil acidity and soils that are deficient in S, because ammonium sulfate
generates higher acidity compared to urea and has about 24% S which urea does not contain.
The use of organic manures and inclusion of legumes in crop rotation can increase the soil
organic matter and N content of the soil, which may improve N use efficiency. In addition, the use of
conservation tillage and improving WUE can also have higher N use efficiency by crop plants. The
use of nitrogen-efficient/acidity-tolerant crop species and genotypes within species is an important
strategy from an economic and environmental point of view, because a significant variation among
crop species and genotypes of the same species has been found among most crop plants. Finally, the
use of an integrated nutrient management model can improve the yield of crops and consequently
higher N use efficiency. Quantitative genetics and molecular approach have a great potential in
increasing N use efficiency in crop plants. However, so far, only limited success has been achieved
through this approach in developing crop cultivars of higher N use efficiency. This may be due to
the lack of interest and/or better cooperation between soil scientists, physiologists, and breeding
