Global mean nitrogen recovery efficiency in croplands can be enhanced by optimal nutrient, crop and soil management practices

An increase in nitrogen (N) recovery efficiency, also denoted as N use efficiency (NUEr), is crucial to reconcile food production and environmental health. This study assessed the effects of nutrient, crop and soil management on NUEr accounting for its dependency on site conditions, including mean annual temperature and precipitation, soil organic carbon, clay and pH, by meta-regression models using 2436 pairs of observations from 407 primary studies. Nutrient management increased NUEr by 3.6-11%, crop management by 4.4–8%, while reduction in tillage had no significant impact. Site conditions strongly affected management induced changes in NUEr, highlighting their relevance for site-specific practices. Data driven models showed that the global mean NUEr can increase by 30%, from the current average of 48% to 78%, using optimal combinations of nutrient (27%), crop (6.6%) and soil (0.6%) management. This increase will in most cases allow to reconcile crop production with acceptable N losses to water. The predicted increase in NUEr was below average in most high-income regions but above average in middle-income regions.


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Behavioural & social sciences Ecological, evolutionary & environmental sciences For a reference copy of the document with all sections, see nature.com/documents/nr-reporting-summary-flat.pdf

Ecological, evolutionary & environmental sciences study design
All studies must disclose on these points even when the disclosure is negative. In this study, we used meta-analytical and meta-regression models, to evaluate and predict the impacts of management practices on NUEr as a function of site factors. We first developed a meta-model by combining existing meta-analytical regression models (n = 29) to predict the change in NUEr in response to agronomic practices and its dependency on site factors. We compared these outcomes to the results of a single meta-regression model based on 2,436 paired observations from 407 primary studies. We finally evaluated the impact of management and site factors controlling NUE, and applied this model to predict the spatial variation of the potential impact of agronomic management practices on NUEr as a function of site factors at a global scale.
For meta-analytical data, we performed a literature search for meta-analytical studies on the effect sizes for NUEr or N uptake in response to changes in nutrient, crop and soil management. Searches were performed using Web of Science (https:// www.webofscience.com) with search terms: NUEr, N uptake, nutrient management, crop management, soil management and metaanalysis. This search and selection resulted in the inclusion of 29 studies. For primary data, the relevant crop, soil and nutrient management data and site-specific factors were retrieved from the 407 primary studies based on the above 29 meta-analytical studies. This resulted in 2,436 paired observations. We estimated the global potential for NUEr improvements on a 0.5 x 0.5 degree resolution using existing global data sets: (1) Ninputs by fertilizer and manure from PANGAEA database (https://doi.pangaea.de/10.1594/PANGAEA.871980); (2) climate data from CRU (http://www.cru.uea.ac.uk/data); (3) land use data from the SPAM dataset (https://www.mapspam.info/data); and (4) soil properties from Soil Grids (http://www.isric.org/explore/soilgrids).
The 29 meta-analytical studies included four criteria: (1) linked to at least one management practice to the impact of NUEr or N uptake; (2) limited to management of main cereal croplands (maize, wheat and rice), excluding grasslands and forests; (3) providing estimates based on field studies, thus excluding laboratory or incubation studies; and (4) when meta-analytical studies presented a summary of previous analyses, only the most recent study was selected. For the 407 primary studies, the following variables were extracted: (1) reference details including author, title and publication year; (2) latitude and longitude; (3) experiment duration; (4) site-specific soil properties and climatic factors; (5) crop type; (6) number of replicates; (7) management practices applied (in predefined crop, soil and nutrient management classes); (8) mean NUE or N uptake in experimental and control treatments; and (9) practices of variation (including standard error, 95% confidence interval, or standard deviation).
Luncheng You and Qi Shao conducted the literature search, screened all literature, extracted all the effect sizes, and coded the information from the studies.
We collected the meta-analytical data from publications before December 2021. A first literature search was conducted in January 2021. Following peer-review process, we updated our search string in Supplementary Note 1. The included studies were published between 1979 and 2021.
Limited to management of croplands, excluding grasslands and forests. Providing estimates based on field studies, thus excluding laboratory or incubation studies.
Our study is an integrated study mainly based on meta-model and published reference data. Our results can be reproduced when following the described methods and data.