Synthetic nitrogen fertilizers deplete soil nitrogen: a global dilemma for sustainable cereal production.
Cereal production that now sustains a world population of more than 6.5 billion has tripled during the past 40 yr, concurrent with an increase from 12 to 104 Tg yr(-1) of synthetic N applied largely in ammoniacal fertilizers. These fertilizers have been managed as a cost-effective form of insurance against low yields, without regard to the inherent effect of mineral N in promoting microbial C utilization. Such an effect is consistent with a net loss of soil organic C recently observed for the Morrow Plots, America's oldest experiment field, after 40 to 50 yr of synthetic N fertilization that substantially exceeded grain N removal. A similar decline in total soil N is reported herein for the same site and would be expected from the predominantly organic occurrence of soil N. This decline is in agreement with numerous long-term baseline data sets from chemical-based cropping systems involving a wide variety of soils, geographic regions, and tillage practices. The loss of organic N decreases soil productivity and the agronomic efficiency (kg grain kg(-1) N) of fertilizer N and has been implicated in widespread reports of yield stagnation or even decline for grain production in Asia. A major global evaluation of current cereal production systems should be undertaken, with a view toward using scientific and technological advances to increase input efficiencies. As one aspect of this strategy, the input of ammoniacal N should be more accurately matched to crop N requirement. Long-term sustainability may require agricultural diversification involving a gradual transition from intensive synthetic N inputs to legume-based crop rotations.
Mulvaney
R L
RL
Department of Natural Resources and Environmental Sciences, Turner Hall, 1102 S. Goodwin Ave., University of Illinois, Urbana, IL 61801, USA. lesssoiln@gmail.com
Khan
S A
SA
Ellsworth
T R
TR
D018533:Biomass; D002523:Edible Grain / Q000254:growth & development* / Q000378:metabolism; D004787:Environmental Pollution; D005308:Fertilizers; D005523:Food Supply; D038622:Internationality; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D012987:Soil / Q000032:analysis*
D005308:Fertilizers; D012987:Soil; D009584:Nitrogen