A team of scientists reports physical attributes and genes that help identify which types of rice use nitrogen efficiently. Such knowledge could help farmers use nitrogenous fertilizers efficiently, save costs, as well as limit nitrogen-linked pollution, which contributes to climate change.
An inter-disciplinary team led by Nandula Raghuram from New Delhi’s Guru Gobind Singh Indraprastha University found that N-use-efficient (NUE) 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 reported 34 genes associated with NUE for potential crop improvement. Their findings have just been published in international journal Frontiers in Plant Science.
For the study, the scientists compared 3 high NUE and 3 low NUE cultivars of rice with normal or low dose of nitrate or urea as the sole source of nitrogen (N).
“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,” Professor Raghuram, who also currently chairs the International Nitrogen Initiative (INI), said in a statement
“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, sulphur etc., which we have not done”, he said.
‘Will be relevant to other cereals’
The researchers studied 25 phenotypic features comparing different cultivars and doses and found that only 20 of them respond to nitrogen-fertilizer, while only 8 of them actually account for NUE. “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-informatic tools used in our study on NUE can be also be used for other difficult crop traits,” said Narendra Sharma, a co-author.
The Indian government’s subsidy on N-fertilizer (mainly urea) is over ₹ 50,000 crore per annum. The farmer pays only a quarter of the market price of urea and harvests a similar proportion of it into grain, at a NUE of 25-30%. The rest of it is lost as N-pollution.
According to the Indian Nitrogen Assessment (2017), agriculture accounts for over 70% of all nitrous oxide emission in the Indian environment, out of which 77% is contributed by fertilizers, mostly urea. Nitrous oxide is a greenhouse gas (GHG) that is 300 times more powerful than carbon dioxide. It has replaced methane as the second largest GHG emission from Indian agriculture over the last 15 years. Cereals account for over 69% of the total consumption of N fertilizers in India, with rice topping the list at 37%, followed by wheat (24%). Hence their importance as target crop for NUE in India and in many parts of the world.