From Agronomy to Molecular Genetics and Proteomics in an Effort to Improve Nitrogen Use Efficiency in Crops - Crop Improvement: New Approaches and Modern Techniques - page 348

Table 11.1 The key parameters involved in uptake and utilization efficiencies of nitrogen in plants
S.N. Components of NUE Formula
1 NUE NUE = S w/ N
2 Usage index UI = S w*( S w/ N )
3 Utilization efficiency UtE = G w/ N t
4 Agronomic efficiecy AE = ( G - G) / N f
5 Physiological efficiency uptake PE = ( G wf- G wc)/ N f - N c uptake
6 Uptake efficiency UpE = N t/ N s
7 Apparent plant recovery AR = ( N t uptake - N c N nitrogen
uptake)/ N t*100
Sw shoot weight, N total nitrogen content of shoots, Gw grain weight, Ns nitrogen supplied in gram
per plant, Nt total nitrogen in plant, Gwf grain weight with fertilizer, Gwc grain weight without
fertilizer (control), Nf nitrogen fertilizer applied, Nf uptake plant nitrogen with fertilizer, Nc uptake
plant nitrogen unfertilized control, PE physiological N-use efficiency, NUE N-use efficiency
PFPN, indicates that maize and rice are able to produce large economic outputs
with respect to applied N fertilizer. These differences may be due to differences in
(1) internal N requirement for plant growth, (2) ability of the plant to translocation
and distribution of N, (3) flag leaf N import/export and leaf senescence pattern
and (4) plant's efficiency in converting CO 2 to carbohydrate (Ladha et al. 1998 ).
Proper N-application rates and timing of application are very important to meet
plant N demand and improve NUE. Studies done by Abdin et al. ( 2005 ) states that
timing of N fertilizer applications does show noticeable results in plant growth and
N uptake with respect to its application. In addition, the application of the fertilizer
at different growth stages of plants determines NUE, which also showed genotypic
variation (Hirel et al. 2007 ).The amount of N that is finally available to the plant can
be improved by using various simple techniques like sustained-release fertilizers,
split applications and other nutrient and crop management strategies (Abdin et al.
2005 ). Nitrogen applications in split doses have shown to enhance the yield, NUE,
and N uptake efficiency in hard red winter wheat under temperate conditions when
compared with fall N applications (Sowers et al. 1994 ). Nitrogen use efficiency
(NUE) in the perspective of photosynthesis is called as photosynthetic nitrogen use
efficiency (PNUE), which is measured as the rate of carbon assimilation per unit
leaf nitrogen (Kumar et al. 2002 ).
Analysis of Variation Nitrogen Use Efficiency
Genotypic differences in the NR levels have been studied and reported by Ab-
din et al. ( 1992 ) in corn, wheat, barley and sorghum. Hakeem et al. ( 2011 , 2012 )
also observed the genotypic differences in the NR levels in rice. Further, Bhatt