In a significant work, Indian biotechnologists have found a way to carry out crop improvement that would help reduce the wastage of nitrogenous (N) fertilisers worth billions of rupees.

While it is known that crops take only about 30 per cent of the N-fertiliser added and the rest gets washed away to water bodies leading to pollution, ill-health and also contributes to climate change. Improving this poor ‘nitrogen use efficiency’ (NUE) was a major global challenge for decades, as there were no simple visual cues or genetic means to differentiate between high and low NUE cultivars in any crop.

Now, an interdisciplinary team led by Nandula Raghuram, professor of biotechnology at New Delhi’s Guru Gobind Singh Indraprastha University (GGSIPU), found some visually identifiable features determining NUE. They also identified some genes that can help crops improve NUE.

Their findings were recently published in the international journal, Frontiers in Plant Science.

Gene identification

For their study, the scientists compared three high NUE and three low NUE cultivars of rice with normal or low dose of nitrate or urea as the sole source of nitrogen (N). They found that N-use efficient cultivars tend to be slow in germination and flowering, grow tall and deep with higher biomass and take longer duration to harvest but yield more with lesser N input. They also identified 34 genes associated with NUE for potential crop improvement.

“Many scientists described on one or two visible or phenotypic features that change in a plant in response to N-fertiliser, but nobody experimentally distinguished N-response from NUE,” said Raghuram, who also currently chairs the International Nitrogen Initiative (INI).

“We were the first in the world to study 25 phenotypic features together in any crop comparing different cultivars, N-forms and doses. We found that only 20 of them respond to N-fertiliser, while only eight of them actually account for NUE,” observed Narendra Sharma, the first author of the paper who earned his PhD degree from this work last year under Raghuram’s guidance.

This finding may be relevant to other cereals and possibly other crops, though they need to be validated, Sharma said.

“The scientific literature is dominated by developed countries that mostly use ammonium nitrate, whereas most developing countries use urea as the main source of N for crops, so we had to compare both nitrate and urea to identify phenotypic features that work for both,” explained Vetury Sitaramam, a former professor of biotechnology at University of Pune who co-led the study. “The present study puts the right tools in the hands of crop scientists to tweak the features of crop plants for a better NUE,” said Tapan Adhya, former Director of the National Rice Research Institute at Cuttack and currently Director of the South Asian Nitrogen Centre of INI.

According to the Indian Nitrogen Assessment (2017), co-edited by Raghuram, Adhya and others, agriculture accounts for over 70 per cent of all nitrous oxide emission in the Indian environment, of which 77 per cent is contributed by fertilisers, mostly urea. Nitrous oxide is a greenhouse gas (GHG) that is 300 times more powerful than carbon dioxide.

Cereals account for over 69 per cent of the total consumption of N fertilisers in the country with rice topping the list at 37 per cent, followed by wheat (24 per cent).