Rethinking sources of nitrogen to cereal crops

Understanding how to manage N inputs to identify the practices that maximize N recovery has been an organizing principle of agronomic research. Because growth in N fertilizer inputs is expected to continue in an ongoing effort to boost crop production over coming decades, understanding how to effici...

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Bibliographic Details
Published in:Global change biology 2020-01, Vol.26 (1), p.191-199
Main Authors: Yan, Ming, Pan, Genxing, Lavallee, Jocelyn M., Conant, Richard T.
Format: Article
Language:English
Subjects:
Agricultural production
Agriculture
Agronomy
Cereal crops
Composts
Corn
Crop production
Crop residues
Crops
Crops, Agricultural
Edible Grain
Farmyard manure
fertilizer
Fertilizers
Manure
Manures
Mineral fertilizers
Nitrogen
Nitrogen isotopes
Organic fertilizers
Organic soils
Recovery
Soil
Soil management
Soils
sustainability
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Summary:Understanding how to manage N inputs to identify the practices that maximize N recovery has been an organizing principle of agronomic research. Because growth in N fertilizer inputs is expected to continue in an ongoing effort to boost crop production over coming decades, understanding how to efficiently manage recovery of fertilizer N will be important going forward. Yet synthesis of published data that has traced the fate of 15N‐labeled fertilizer shows that less than half of the N taken up by crops is derived from current‐year N fertilizer. The source of the majority of N in crops is something other than current‐year fertilizer and the sources are not really known. This is true for maize (only 41% of N in crops was from current‐year N fertilizer), rice (32%), and small grains (37%). Recovery of organic fertilizer N (manure, green manure, compost, etc.) in crops is low (27%), though N recovery in subsequent years (10%) was greater than that for mineral fertilizers. Thus, while research on efficiency of N fertilizer use through improved rate, type, location, and timing is important, this research fails to directly address management of the majority of the N supplied to crops. It seems likely that the majority of non‐fertilizer N found in crops comes from turnover of soil and crop residue N. We encourage the research community to revisit the mental model that fertilizer is a replacement for N supply from turnover of soil organic N (SON) and consider a model in which N fertilizer augments ongoing SON turnover and makes an important longer term contribution to SON maintenance and turnover. Research focused on the efficient recovery of N current‐year fertilizer inputs neglects this potential role for building soil N and managing soil N turnover, which seems likely to be the most important source of crop N. We synthesized 15N fertilizer studies and integrated these with other N budget data to better understand the source of the N found in cereal crops. Most crop N comes from a source other than current year's fertilizer. We believe that research focused on the efficient recovery of N current‐year fertilizer inputs neglects the role for building soil N and managing soil N turnover, which seems likely to be the most important source of crop N.
ISSN:1354-1013
1365-2486
DOI:10.1111/gcb.14908