Study shows large differences in nitrogen efficiency of Indian rice varieties

Nitrogen efficiency refers to the yield of a crop in relation to the nitrogen available to it (natural and artificial) | Image credit: The Hindu

Biotechnologists at Guru Gobind Singh Indraprastha University (GGU) have found that the ability of rice varieties commonly grown in India to utilize nitrogen varies considerably. This knowledge can be used to develop newer varieties that use less nitrogen and produce higher yields, drastically reducing expenditure on imported fertilizers and reducing nitrogen pollution.

“Two-thirds of all urea in India is used for crops, most notably rice. Poor nitrogen use efficiency (NUE) of fertilizers results in wastage of N (nitrogen fertilizers) worth Rs 1 trillion per year in India and over $170 billion per year globally,” said N. Raghuram, Professor at GGU and lead author of the study, while announcing the findings.

Nitrogen efficiency is the yield of a crop in relation to the nitrogen available to it (natural and artificial).

“Worse still, nitrogen fertilizers are the major source of nitrous oxide and ammonia pollution in air and nitrate and ammonium pollution in water, which affect our health, biodiversity and climate change. Yet we do not have a ranking of Indian crop varieties in terms of their NUE for crop improvement through selection or breeding,” said Dr Raghuram.

The article was published in the peer-reviewed journal late last week. Journal of plant growth regulation.

The NUE of the best varieties was five times higher than that of the worst, the study found. However, high NUE does not always mean the highest yields, and farmers in India generally prefer varieties with the highest yields.

“For a long time, the focus of Indian agriculture was solely on increasing yields. This was necessary during the Green Revolution, but it also meant more artificial fertilizers, more wastage and pollution. India has tens of thousands of rice varieties, but only a few are actually used and studied in agricultural research. To find newer crops that improve NUE and yields, we need to take a broader approach,” said Dr Raghuram. The Hindu.

Co-authors of the study were Ashu Tyagi and Navjyoti Chakraborty, both scientists at the Centre for Sustainable Nitrogen and Nutrient Management in the School of Biotechnology at GGU.

While some improvements in NUE could be achieved through improved fertilizer formulations, pulse-based crop rotations and crop management practices, there is now a need to place more emphasis on crop improvement through biotechnology, the study authors said.

“Our study of a dozen rice varieties from over a thousand varieties registered in India found a five-fold variation in NUE that can be exploited to improve crop yields. There may be even greater potential in the tens of thousands of unused varieties/landraces left by farmers,” said Ms Tyagi, who carried out this work for her PhD. “This was by far the most comprehensive study of 46 phenotypic and physiological parameters in a crop. We found 19 parameters that are strongly associated with NUE, including eight that we discovered for the first time and which need to be confirmed in field trials,” she added.

The studies are based on research conducted over a decade by different researchers in the laboratory on different sets of 34 released rice varieties, using a consistent methodology to assess NUE in the university greenhouses, plots on campus that simulate agricultural fields.

“The varieties that we had previously identified as high-value NUE varieties in the greenhouse were later confirmed in the field by our partners in agricultural institutes. Therefore, we are increasingly confident that we have a reliable, field-relevant method for biological evaluation of NUE. On this basis, we can recommend a large-scale survey of all Indian rice varieties to find more and more NUE varieties suitable for different agro-climatic conditions and markets,” said Dr Raghuram.

India is the world’s second-largest source of nitrous oxide (N2O), a greenhouse gas that warms the atmosphere far more than carbon dioxide. Nearly 11% of these human-caused emissions in 2020 came from India, only ahead of China at 16%. The main source of these emissions is fertilizer use, according to a global assessment of N2O emissions conducted in June.