KCYNUECE

3094

8 avril 2021 10:25

8 avril 2021 10:25

Commercial extraction of nitrogen (N) from the atmosphere began soon after World War II and has provided N fertilizer that has transformed agriculture to meet, through greater crop areas and yields although with some regional shortfalls, the increasing food demand of a world population that has increased from 2 billion then to 7.6 billion in 2018. N fertilizer now provides more N input to agriculture (113 Mt N/year) than biological N fixation by legumes (33–46 Mt N/year) on which earlier agriculture relied entirely. Persistent claims over the last decade for return to organic methods, which include rejection of fertilizer N, are based on studies that erroneously claim adequate productivity to feed the world. Previous analyses, by contrast, have estimated that organic agriculture (OA) could at best support a world population of three to four billion. The problem is two-fold. First, organic crops grown in sequences with legumes or treated with N manures mostly yield less than crops grown with N fertilizer. Second, substantial areas of legumes are required to provide adequate N for required yields of non-legume crops. Recent analyses have overestimated the yield of organic crops by omitting the effect of weeds, pests and diseases, and by ignoring the land required for legumes. The result is a large overestimation of the relative productivity of OA. The effect of area is critical because, since there is little opportunity to increase cropping area beyond the current 1400 Mha, land for legumes means less land for, and consequently lower total production from, non-legume food crops. To replace 100 Mt N fertilizer/year with legumes at a net fixation of 100 kg N/ha/year would leave just 30% of cropland available for non-legumes producing a similar proportion of current yield. Even with major gains in yield, organic systems cannot feed our populous world and less so as the population increases to an expected 9.8 billion by 2050.

None

• AB - Spécifique
• FREDO alimentation humaine
• FREDO durabilité
• FREDO fertilisation
• GEO Royaume-Uni
• azote
• land use
• légumineuses
• rendement
• yield

• n fertilizer
• biological nitrogen fixation
• demand and security
• food productivity
• land allocation
• legume and non-legume crops
• organic agriculture
• world population and growth

Outlook on Agriculture

47

277-282

December 1, 2018

1 décembre 2018

10.1177/0030727018805765 Le DOI est une URL unique de référencement d'une publication. Il est donc plus fiable et permanent qu'une URL classique

0030-7270 L’ISSN est un code de 8 chiffres servant à identifier les journaux, revues, magazines, périodiques de toute nature et sur tous supports, papier comme électronique.