Crops take only about 30 per cent of the nitrogen fertilizer added and the rest gets washed away to cause pollution, ill-health and 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.
A team of researchers led by Prof. Nandula Raghuram from Guru Gobind Singh Indraprastha University, (GGSIU) New Delhi, has found the ‘phenotype’ or the visually identifiable features determining NUE. They also identified some associated genes that could help in crop improvement for NUE.
“Many scientists described on one or two visible or phenotypic features that change in a plant in response to N-fertilizer, but nobody experimentally distinguished N-response from NUE” said Prof. N Raghuram, Professor, GGSIU, who also currently chairs the International Nitrogen Initiative (INI).
The team compared 3 high NUE and 3 low NUE cultivars of rice with a 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 a longer duration to harvest but yield more with lesser N input.
They also reported 34 genes associated with NUE for potential crop improvement.
“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-fertilizer, while only 8 of them actually account for NUE” added Dr Narendra Sharma, the first author of the article. “Even out of these 8 features mentioned in the title, only 6 are common to different forms of N in fertilizers such as nitrate or urea. The effects of nitrate on root length and flowering were not significant”, he added.
As the studies have been done on rice, will it be applicable to other crops too? Answering this Dr Sharma said, “Our findings in rice will also be relevant to other cereals and possibly other crops, though they need to be validated. More importantly, the statistical and bio-informatics tools used in our study on NUE can be also be used for other difficult crop traits”.
Speaking on the importance of the study Prof Raghuram said “Moreover, most of the crop improvement for yield is focused on reducing crop duration and biomass to maximize grain output over everything else. Our work indicates that unless scientists bring NUE traits together with yield traits through breeding, we may be gaining yield at the cost of NUE. We also need to worry about whether this is also true for other inputs such as phosphorus, water, potassium, sulfur etc., which we have not done”.
The research findings have been published in the journal Frontiers in Plant Science. The research team includes Narendra Sharma, Vimlendu Bhushan Sinha, Ashwani Jha and Prof N Raghuram from School of Biotechnology, GGSIU, D. Subrahmanyam, C.N. Neeraja, K Surekha and N. Arun Prem Kumar from Indian Council of Agriculture Research (ICAR) Indian Institute of Rice Research, Hyderabad, Rajender Prasad from ICAR Indian Agricultural Statistics Research Institute, New Delhi and Vetury Sitaramam from Anant Cooperative Housing Society, Pune. (India Science Wire)
