Potential impact of population trends

The growth of world population, to around 6.7 billion in 2008 according to the World Bank (2010), is expected to continue for some decades into the future, reaching perhaps 9 billion by 2040. An inevitable consequence of such growth is more intensification of food production. Erisman et al (2008) estimate that, by 2008, nitrogen fertilizers manufactured by the Haber-Bosch process made possible the feeding of virtually half of all humanity. Nevertheless the conversion of fertilizer N to protein N is low. For example, in 2005, approximately100Tg of N from the Haber-Bosch process was used in global agriculture, whereas only 17Tg of this was consumed by humans in crop, dairy and meat products (UNEP and Woods Hole Research Center, 2007). As pointed out by Erisman et al (2008), although livestock provide many other benefits in addition to meat and milk (for example transport, hides and wool), this highlights the extremely low nitrogen-use efficiency in agriculture.

Erisman et al, on the basis of work by Tilman et al (2002) and the International Fertilizer Association (2007), conclude that the global nitrogen-use efficiency in the production of cereals decreased from ~80 per cent in 1960 (when N application rates were generally low by modern standards) to ~30 per cent in 2000. This latter value is even lower than those arrived at elsewhere in this book: around 50 per cent by Bouwman et al in Chapter 5, and 40 per cent by the present author and colleagues in Chapter 4, based on different sources in the literature. In spite of these uncertainties, it seems safe to conclude that more than half of all fertilizer N is currently lost by denitrification to N2O and N2, volatilization as ammonia and leaching of nitrate. All these loss mechanisms lead to N2O emissions, whether direct or indirect, and it is evident that an improvement in the efficiency with which fertilizer N is used in the future would mean that some of the extra food required in the future could be produced without a matching increase in fertilizer N use, thus avoiding additional N2O emissions. Smil (2001) and Erisman et al (2008) both suggest that a 50 per cent increase in N use efficiency is achievable.

0 0

Post a comment