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 343

Fig. 11.1 Crop production of India in the past 50 years
food production for increasing population, since most of the available is already
under cultivation, and in many areas land cannot be used for intensified produc-
tivity because of rapid urbanization and increasing environmental pollution. To-
gether, all of these issues have forced a great challenge on Indian agriculture for
developing novel approaches that can increase crop productivity on the cultivable
land. Development of high-yielding wheat and rice varieties and use of chemical
fertilizers have made enormous contribution in doubling crop production of India
in the past 50 years. The production of wheat and rice in 1950-1951 was 6.46 and
20.57 million tonnes, respectively, which has increased to 76.2 and 85.9 million
tonnes in 2008-2009 (Directorate of Economics and Statistics 2008 ) (Fig. 11.1 ).
In order to increase crop production, the consumption of N fertilizer has increased
up to 10-folds in last 50 years globally (Lian et al. 2005 ), because high-yielding
present crop varieties have high demands for N. The problem lies in the, nitrogen
use efficiency (NUE) which is as low as 33 % for cereals on global basis (Raun and
Johnson 1999 ). The unutilized 60-70 % caused severe environmental hazards. It is,
therefore, necessary to control too much input of chemical N fertilizers into the field
by enhancing the NUE of the crops.
N-assimilation Processes in Plants
Nitrate (NO 3 - ) is the major resource of nitrogen for most of the cultivated crops.
The first step in acquisition of nitrate is its uptake by root cells. NO 3 - reaches the
aerial organs by moving out in the external medium from root cell or by unloading
in the xylem vessel (Kant et al. 2011 ). NO 3 - assimilation takes place in leaves and