National Geographic : 2013 May
100 national geographic • may 2013 SAHARA Gulf of Mexico Chesapeake Bay Lake Erie Yan gt zeMississippi Lake Tai CHINA TAIWAN TANZANIA KENYA NIGERIA MALAWI INDIA UNITED STATES AFRICA ASIA AUSTRALIA SOUTH AMERICA NORTH AMERICA EUROPE -200 220 Deficiency Little or no cropland Excess 0 Average annual nitrogen balance, pounds per acre Global inputs and outputs LEGUMES** MANURE United States India Africa Rest of world AIR POLLUTION* EXCESS remaining after harvest SYNTHETIC FERTILIZER HARVESTED WITH PLANT OUT 53% 59% IN China Feast or Famine Nearly half the people on the planet wouldn’t be alive if not for the abundant food made possible by nitrogen fertilizer. Yet its benefits have not reached everyone. In sub-Saharan Africa, where 239 million people go hungry in a year, crops fail as soil is stripped of nutrients, and farmers can’t afford to buy fertilizer. Elsewhere overuse pol- lutes waterways and releases greenhouse gases. THe FlOW OF NITrOgeN Synthetic fertilizer provides most of the nitrogen that makes soil fertile worldwide. Almost half the nitrogen is then harvested with crops; the rest is lost through leaching, erosion, and emissions. *Pollutants from fossil fuels, such as nitrous oxides and ammonium, can be deposited on soil. **Bacteria in the roots of legumes fix atmospheric nitrogen, convert- ingittoaform plants can use.