* Nutrients that feed the world damage the environment
* More efficient use would offer multiple benefits
* Report calls for inter-governmental cooperation
By Nina Chestney
LONDON, Feb 18 (Reuters) - More efficient use of nitrogen fertilisers could cut annual consumption by 20 million tonnes, help the environment and save $170 million a year by the end of the decade, scientists said in a report on Monday.
Nitrogen, phosphorous and other nutrients essential for plant growth have long been used in fertilisers to meet world food and energy demand.
It is estimated that nitrogen and other mineral fertilisers help to feed about half the world's population, which is set to rise to 9 billion people by 2050 from the 7 billion today.
However, the excessive use or misuse of fertilisers can also release harmful greenhouse gases into the atmosphere and nitrate and phosphate compounds into water, contributing to soil erosion and damage to ecosystems.
The global annual cost of damage from nitrogen pollution alone is about $800 billion. But improving the efficiency of nutrient use by 20 percent by 2020 would not only save money, the report commissioned by the United Nations Environment Programme (UNEP) said.
"Our analysis shows that by improving the management of the flow of nutrients we can help protect the environment, climate and human health, while addressing food and energy security concerns," said Mark Sutton, lead author of the report and professor at Britain's Centre for Ecology and Hydrology.
While many sub-Saharan African farmers struggle to access enough nutrients to produce good-quality crops, excessive use of nutrients by rich and rapidly developing countries is threatening the climate and biodiversity.
Current nutrient use is not very efficient. On average, more than 80 percent of nitrogen and 25-75 percent of phosphorous are lost to the environment and the energy used to prepare them is wasted.
The UNEP report's co-author Oene Oenema, of Wageningen University in the Netherlands, says that 4-12kg of both nitrogen and phosphorous are needed to produce 1kg each of the two nutrients in the food on a consumer's plate.
The study, carried out by nearly 50 experts in 14 countries, calls for an inter-governmental framework to tackle inefficient nutrient use.
Lead author Sutton said that the motivation to take action would be much stronger if governments joined forces to meet the multiple global challenges for food, climate, health and energy, water and air pollution.
One option could be to include rules on nutrient use in the 1995 UNEP agreement to prevent the degradation of marine environments from land-based activities.
Improvements should be made to the management of soil, crops, livestock and manure, the report said. Nutrient loss from industry and waste water treatment could also be reduced and the rate of nutrient recycling increased.
The study also said that individuals and governments should consider ways of lowering the amount of meat and dairy eaten where there are high rates of consumption and waste.
"With rapidly increasing meat and dairy consumption, as Asia and Latin America aspire to European and North American norms, our diet choices have a huge potential to influence future levels of global nutrient pollution," it said. (Editing by David Goodman)