Nitrogen Fertility Status of the Indian Soils vis-a-vis the World Soils

摘要

Nitrogen (N) is a vital component of plants and animals. Nitrogen in soil-plant system is subject to continuous transformations and the soil organic matter forms the largest stable pool of soil-N. Crop-N needs over and above the resident soil N supply are often met through the use of N fertilisers. Over-use of N fertilisers and manures, however, brings forth many environmental issues. Soil-N supplies need to be duly factored in making N fertiliser recommendations to sustain ecologically justified crop production. Assessment of soil N status can help gauge the environmental footprints of increased dependence on external N supplies. It can also aid in identifying the soils that can respond to increased N application and can even guide in N- fertiliser production and movement policy. Review of research work on the subject reveals that light textured soils and salt-affected soils the world-over continue to be greatly limited by soil N supplies. Contrarily, soils developed on organic materials are provided with adequate N. Assessment of N balance identifies Sub Saharan Africa (SSA) region with a meagre 1.5% of total fertiliser N consumption as greatly limited by N supplies. However, some parts of the countries like China draw heavily on N fertilisers for crop production and thus threaten the environmental balance. A recent comprehensive study on assessment of soil N status in 173 districts of India reported almost all zones having low N-fertility status. The way forward is to address the low N use efficiency (NUE) in developing countries and to ensure need-based efficient use of N fertilisers. Sandy and salt-affected soils need preferential consideration in nitrogen research. Obligatory carbon nitrogen link hints at the importance of adoption of carbon sequestration measures in raising soil N fertility status and consequentially the crop production.