Recently, a team of scientists have discovered how rice crops could be efficiently grown and cultivated by reducing the wastage of nitrogenous (N) fertilisers in order to save costs, and limit nitrogen related pollution. The inter-disciplinary team of researchers was led by Nandula Raghuram, serving as the Chairman of the International Nitrogen Initiative (INI), and Professor of Biotechnology in Guru Gobind Singh Indraprastha University (GGSIPU), New Delhi. The study based on nitrogen use efficiency in rice, was published in the international journal, Frontiers in Plant Science.
For many decades, the process for improving a nitrogen use efficient (NUE) cultivar has been a really tedious and challenging task for scientists at a global scale. There were no simple visual features and genetic evidences that could distinguish between the high or low NUE cultivars in any of the observed crops.
Usually crops utilise only around 30 per cent of the N-fertiliser and the remaining of these fertilisers gets washed away to the nearby water bodies leading to pollution, spread of diseases, and negative impacts on the climate.
However, the team of GGSIPU have discovered some visual evidences for determining the NUE cultivars. Genetic features were also found which could potentially help crops improve NUE.
Identification of Genes
The study was conducted by comparing three high and three low NUE cultivars of rice with normal to minimal dose of nitrate or urea as the primary source of nitrogen (N). It was found that the N-use efficient cultivars were slow in germination and flowering, grew taller and deeper with higher biomass. Though they took a longer period to harvest, they yielded more with less amount of nitrogen usage. The team also discovered around 34 genes, associated with the NUE, which could be essential for crop improvement. Though most of the scientists had mentioned about one or two phenotypic features that change in a plant in response to N-fertiliser, no one could experimentally differentiate the N-response from NUE.
This is the first time scientists have successfully studied 25 phenotypic features in any crop comparing different N-forms, cultivars and doses, the world over. The researchers observed that only 20 of them had responded to N-fertiliser, while only eight of them were associated with NUE. According to them, majority of the crop improvement for yield puts emphasis on minimising crop duration and biomass to maximise grain output over the other aspects. They came to know that unless the scientists work on combining NUE traits along with yield traits, NUE would be compromised. They are yet to perform research over whether this was applicable for other inputs including phosphorus, water, potassium, sulphur, etc.
Relevance of the Study to Other Cereals and Crops
As per the scientists, their findings would be relevant to other cereals and crops as well. However, further research might be required in order to validate the same. They also said that the statistical and bio-informatic tools used in their study on NUE could also be used for identifying other difficult crop traits.
About the Nitrous Oxide Emissions
As per the Indian Nitrogen Assessment report of 2017, agriculture contributes over 70 per cent of all nitrous oxide emissions in the Indian environment of which about 77 per cent is contributed by chemical fertilisers. Nitrous oxide (N2O) is a greenhouse gas (GHG) which is around 300 times more powerful than carbon dioxide (CO2) and has replaced methane (CH4) as the second largest GHG emission from Indian agriculture over the last 15 years.
Over 69 per cent of the N fertilisers in India are consumed by cereal crops, out of which, rice has the majority of N-consumption with 37 per cent, and wheat at the second place with 24 per cent.
Consumption of N-fertilisers by Indian Farmers
Indian government provides subsidies of more than ` 50,000 crores per annum on N-fertilisers (mostly urea). Farmers pay only a quarter of the market price of urea and harvest a similar proportion of it into grain, at a NUE of 25-30 per cent. The rest of these fertilisers are lost as N-pollution.
Therefore, there is need to figure out a method to reduce crop duration, which has been an important research goal in Indian agriculture, with little loss of NUE in the process.
Conclusion
Plant NUE is a complex trait which is determined by quantitative trait loci and influenced by environmental changes and its integration of NUpE (Nitrogen Uptake Efficiency) and NUtE (Nitrogen Utilisation Efficiency). Enhanced NUE can be achieved by genetically modifying plants and integrated agricultural management practices. Thus, developing an integrated research programme is a major objective in the future, based on whole-plant physiology, quantitative genetics, forward and reverse genetics, and agronomy approaches to improve NUE.
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