Nitrogen, the vital primary plant growth nutrient at deficit soil conditions, drastically affects the growth and yield of a crop. Over the years, excess use of inorganic nitrogenous fertilizers resulted in pollution, eutrophication and thereby demanding the reduction in the use of chemical fertilizers. Being a C4 plant with fibrous root system and high NUE, maize can be deployed to be the best candidate for better N uptake and utilization in nitrogen deficient soils. The maize germplasm sources has enormous genetic variation for better nitrogen uptake contributing traits. Adoption of single cross maize hybrids as well as inherent property of high NUE has helped maize cultivars to achieve the highest growth rate among the cereals during last decade. Further, considering the high cost of nitrogenous fertilizers, adverse effects on soil health and environmental impact, maize improvement demands better utilization of existing genetic variation for NUE via introgression of novel allelic combinations in existing cultivars.
Furthermore, there is reason to question the usefulness of many traditional NUE formulations, and to consider factors to improve the conceptualization of NUE for future use. As a resource for agricultural researchers and students, here we present a comprehensive list of NUE indices and discuss their functions, strengths, and limitations. We also suggest several factors—which are currently ignored in traditional NUE indices—that will improve the conceptualization of NUE, such as: accounting for a wider range of soil N forms, considering how plants mediate their response to the soil N status, including the below-ground/root N pools, capturing the synchrony between available N and plant N demand, blending agronomic performance with ecosystem functioning, and affirming the biological meaning of NUE.
In the last six decades, the consumption of reactive nitrogen (Nr) in the form of fertilizer in India has been growing rapidly, whilst the nitrogen use efficiency (NUE) of cropping systems has been decreasing. These trends have led to increasing environmental losses of Nr, threatening the quality of air, soils, and fresh waters, and thereby endangering climate-stability, ecosystems, and human-health. Since it has been suggested that the fertilizer consumption of India may double by 2050, there is an urgent need for scientific research to support better nitrogen management in Indian agriculture. In order to share knowledge and to develop a joint vision, experts from the UK and India came together for a conference and workshop on “Challenges and Opportunities for Agricultural Nitrogen Science in India.” The meeting concluded with three core messages: Soil stewardship is essential and legumes need to be planted in rotation with cereals to increase nitrogen fixation in areas of limited Nr availability.
2. NITROGEN USE EFFICIENCY
Nitrogen Use Efficiency (NUE) includes N uptake,
utilization or acquisition efficiency and expressed
as a ratio of output (total plant N, grain N, biomass
yield, grain yield) and input (total N, soil N or N-
fertilizer applied).
NUE = UpE X UtE
where
UpE (nitrogen uptake efficiency)
UtE (nitrogen utilizing efficiency)
4. CROP TRAIS TO IMPROVE ‘N’ USE EFFECIENCY
N use efficiency may be improved by
1) Minimising the amount of N that is required in the
crop to capture the majority of the radiation and to use
this efficiently to produce dry matter,
2) Increase the efficiency with which the crop is able
to acquire N that is mineralised from organic residues
or from applications of inorganic fertiliser.
3) Increasing yield without increasing fertiliser N
requirement
5. MOLECULAR PHYSIOLOGY OF NITROGEN UPTAKE
AND ASSIMILATION
Productive agriculture needs a large amount of expensive
nitrogenous Fertilizers. Improving nitrogen use efficiency (NUE)
of crop plants is thus of key importance.
NUE definitions differ depending on whether plants are
cultivated to produce biomass or grain yields.
However, for most plant species, NUE mainly depends on how
plants extract inorganic nitrogen from the soil, assimilate nitrate
and ammonium, and recycle organic nitrogen.
Efforts have been made to study the genetic basis as well as the
biochemical and enzymatic mechanisms involved in nitrogen
uptake, assimilation, and remobilization in crops and model
plants.
The detection of the limiting factors that could be manipulated
to increase NUE is the major goal of such research.
6. NITRATE UPTAKE
Nitrate uptake occurs at the root level
two nitrate transport systems have been shown to
coexist in plants and to act co-ordinately to take up
nitrate from the soil solution and distribute it within
the whole plant
7. NITROGEN ASSIMILATION
Plants absorb nitrogen mostly as NO-
3 and NH+
4.
Most of the nitrate absorbed by roots is translocated to
leaves by transpiration stream.
Nitrate assimilation is, mainly carried out in leaves and
a small fraction in roots.
NO3 + NADH + H+ Nitrate reductase NO-2 + NAD+ + H2O
NO-2 + 6e _ + 7H+ Nitrite reductase NH3 + H2O
