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N, P and K Surplus Cut By Almost Half

12 April 2011

DENMARK - The surplus of N, P and K from agriculture has fallen considerably in the past couple of years according to a new survey from Aarhus University.


The surplus of nutrients from agriculture has in the past couple of years been markedly lower than in previous years. Photo: Janne Hansen

Scientists from the Department of Agroecology and Environment at Aarhus University have over the course of several years calculated the surplus of nutrients from agriculture. They have found that excess N, P and K has been cut by almost half from the middle of the 1980s to the middle of the 2000s, at which time the decrease has stagnated.

However, the latest results show that nutrient surplus has once again fallen markedly in the past couple of years.

The surplus of N has decreased by approximately 10 percent compared to the results found in connection with the Aquatic Action Plan III (VMPIII) midway evaluation. With respect to P and K the decrease has been even greater.

The relatively large decrease seen in the past couple of years is closely related to the increasingly larger winter cereals area concurrent with favourable weather conditions that have resulted in higher yields in 2008 and 2009. These factors have led to a considerably greater amount of N, P and K being removed via the harvested crops in the past two years compared to previous years.

- It must also be mentioned that next year's surplus will probably increase, partly because of relatively poorer yields in 2010 and partly because more commercial fertilizer has been purchased, particularly P and K, compared to the year before, says senior scientist Finn Pilgaard Vinther from the Department of Agroecology and Environment.

Nitrogen surplus was calculated as the difference between what is supplied to agriculture via commercial fertilizer, feed, nitrogen fixation in clover and other legumes, and rainwater, and what is removed from agriculture via harvested crops such as grain and oilseed and animal products such as meat, milk and eggs.

It is basically a household budget in which income minus expenses gives a surplus. It does not say anything about the internal turnover, where much of the surplus disappears via evaporation of ammonia, denitrification, incorporation in the soil's organic pool, or leaching. It is therefore not possible to say that nitrogen surplus is equal to nitrogen leaching.

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