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Anthropogenic activities have altered the global nitrogen (N) cycle in a massive way. With a consumption of 15.5% of the global production of fertilizer-N in the cropping year of 2015–16 and increase in energy and transport due to increasing societal aspirations, India illustrates a dual challenge to food production and environmental protection vis-a-vis release of reactive-N (NR). While necessity for considering the usefulness of the NR challenge for India is apparently more of economic nature, considering the huge subsidy burden to the country's exchequer for fertilizer-N, additional environmental burden including adverse climate and associated health impacts are of great concern. Thus an in-depth analysis and policy intervention to stem the tide should be a win–win option.

The crops respond to applied nitrogen fertilizers, but are unable to express their full genetic potential due to decline in the availability of nitrate during later stages of crop growth. When nitrate is maintained in the soil during reproductive phases of crop growth, higher activity of N assimilatory enzymes in the upper leaves leads to an increased grain N. There is therefore, need to synchronize the supply with the requirement of the plant. This was tried through modification in the management practices. Higher activity of the enzyme nitrate reductase was maintained when nitrogen was provided at later stages of crop growth, leading to increased grain N.

The ready availability of industrially fixed reactive nitrogen (Nr) has resulted in a substantial accumulation of Nr in the biosphere. Proper management of Nr is necessary to minimize its negative consequences, while allowing maximization to its positive benefits. An integrated Nr assessment which has not yet been undertaken for India, would be prudent given the future population projections. Basic concepts of an integrated scientific assessment are discussed and two previous integrated Nr assessments (USA and Europe) are compared and contrasted to provide examples from which to draw upon for the design and implementation of an India integrated Nr assessment.

Summary Photorespiratory nitrogen metabolism in the C 3 -C 4 intermediate species, Moricandia arvensis , was studied in comparison with barley (C 3 ) and sorghum (C 4 ). The rate of photorespiratory ammonia accumulation in the presence of methionine sulphoximine in M. arvensis was 40 % of that observed in barley leaves. The activities of glycolate oxidase and glycine decarboxylase were about 15 and 30 % lower, respectively, in the leaves of M. arvensis when compared to those in barley. Glyoxylate aminotransferases activities with various amino donors were similar in barley and M. arvensis . The accumulation of total glycine in response to treatment with isonicotinylhydrazide was high in barley leaves and low in sorghum and M. arvensis . It is likely that the apparent turnover of the photorespiratory glycine pool is slower in M. arvensis and that this could be a factor responsible for the reduced rates of photorespiration observed in this C 3 -C 4 intermediate species.

Summary The capacity to reassimilate carbon dioxide originating from 14 C-labelled photorespiratory substrates has been investigated in Parthenium hysterophorus , a C 3 -C 4 intermediate species in comparison with wheat (C 3 ) and sorghum (C 4 ). Dark/light ratios of 14 CO 2 evolution from either labelled glycolate or glycine by the leaf slices of P. hysterophorus were intermediate to those of wheat and sorghum, indicating that P. hysterophorus possesses an enhanced capacity for internal refixation of 14 CO 2 produced during photorespiration. The rate of ammonium accumulation caused by methionine sulfoximine (MSO) in the leaves of P. hysterophorus was also intermediate to those observed with the leaves of C 3 and C 4 plants.