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Conservation agriculture is often assumed to reduce soil N2O emissions. Yet, studies analyzing the specific effect of conservation agriculture practices on N2O emissions give contradictory results. Herein, we synthesized a comprehensive database on the three main conservation agriculture practices (cover crops, diversified crop rotations, and no-till and/or reduced tillage (NT/RT)) to elucidate the role of conservation practices on N2O emissions. Further, we used a random meta-forest approach to identify the most important predictors of the effects of these practices on soil N2O emissions. Averaged across all comparisons, NT/RT significantly decreased soil N2O emissions by 11% (95% CI: –19 to –1%) compared to conventional tillage. The reductions due to NT/RT were more commonly observed in humid climates and in soils with an initial carbon content < 20 g kg–1. The implementation of cover crops and diversified crop rotations led to variable effects on soil N2O emissions. Cover crops were more likely to reduce soil N2O emissions at neutral soil pH, and in soils with intermediate carbon (~20 g kg–1) and nitrogen (~3 g kg–1) contents. Diversified crop rotations tended to increase soil N2O emissions in temperate regions and neutral to alkaline soils. Our results provide a comprehensive predictive framework to understand the conditions in which the adoption of various conservation agriculture practices can contribute to climate change mitigation. Combining these results with a similar mechanistic understanding of conservation agriculture impacts on ecosystem services and crop production will pave the way for a wider adoption globally of these management practices. [ABSTRACT FROM AUTHOR]

This study evaluates the dynamics of soil organic carbon (SOC) under perennial crops across the globe. It quantifies the effect of change from annual to perennial crops and the subsequent temporal changes in SOC stocks during the perennial crop cycle. It also presents an empirical model to estimate changes in the SOC content under crops as a function of time, land use, and site characteristics. We used a harmonized global dataset containing paired‐comparison empirical values of SOC and different types of perennial crops (perennial grasses, palms, and woody plants) with different end uses: bioenergy, food, other bio‐products, and short rotation coppice. Salient outcomes include: a 20‐year period encompassing a change from annual to perennial crops led to an average 20% increase in SOC at 0–30 cm (6.0 ± 4.6 Mg/ha gain) and a total 10% increase over the 0–100 cm soil profile (5.7 ± 10.9 Mg/ha). A change from natural pasture to perennial crop decreased SOC stocks by 1% over 0–30 cm (−2.5 ± 4.2 Mg/ha) and 10% over 0–100 cm (−13.6 ± 8.9 Mg/ha). The effect of a land use change from forest to perennial crops did not show significant impacts, probably due to the limited number of plots; but the data indicated that while a 2% increase in SOC was observed at 0–30 cm (16.81 ± 55.1 Mg/ha), a decrease in 24% was observed at 30–100 cm (−40.1 ± 16.8 Mg/ha). Perennial crops generally accumulate SOC through time, especially woody crops; and temperature was the main driver explaining differences in SOC dynamics, followed by crop age, soil bulk density, clay content, and depth. We present empirical evidence showing that the FAO perennialization strategy is reasonable, underscoring the role of perennial crops as a useful component of climate change mitigation strategies. [ABSTRACT FROM AUTHOR]

Emphasis is placed on developing robust, productive, economically competitive, and environmentally benign agroecosystems. In 2012, after 18 yr of a study to evaluate the effects of crop sequence and tillage, we measured soil properties at various depths to 91.4 cm and estimated soil C. The experiment, near Mandan, ND, was a split-plot design, with crop sequence as whole plots and tillage (minimum tillage or no-till) as subplots. Crop sequences included continuous spring wheat (Triticum aestivum L.) with crop residue retained or removed, spring wheat--millet [Setaria italica (L.) Beauv.], spring wheat--safflower (Carthamus tinctorius L.)--fallow, spring wheat--safflower--rye (Secale cereale L.) and spring wheat--fallow. Soil organic C, calculated by the equivalent mass method (SOCem), was consistently higher (P < 0.001) than when calculated by the fixed-depth method. Disparities between the two methods, greatest near the soil surface, were attributable to tillage. Estimates of SOCem were not affected by cropping sequence at any depth, averaging about 26, 47, 73, 114 and 156 Mg ha-1 in the 0- to 7.6-, 0- to 15.2-, 0- to 30.5-, 0- to 61.0-, and 0- to 91.4-cm partitions. Tillage had no influence at depths <30.5 cm, but no-till plots contained more SOCem than minimum tillage plots in the 0- to 61-cm (115 vs. 112 Mg ha-1 ) and 0-to 91.4-cm (158 vs. 153 2.3 Mg ha-1 ) partitions (P < 0.05). Soil organic C in the 0-to 7.6-cm depth increased by an average of 3.2 Mg ha-1 or 16% since 2001. This study suggests that C sequestration in soil is less impacted by the choice of crop sequence than by tillage. [ABSTRACT FROM AUTHOR]

Woody plant expansion has been documented on grasslands worldwide as a result of overgrazing and fire suppression, but changes in ecosystem structure and function accompanying this phenomenon have yet to be extensively studied in the temperate semi-arid grasslands of North America. The primary objectives of this study were to determine the influence of woody plant expansion on soil carbon (C), soil nitrogen (N), and roots to a depth of 15 cm along a 42-year (1963–2005) chronosequence encompassing grassland, woodland, and transition zones in a northern Great Plains grassland. From these data, we also estimated ecosystem-level soil C and N changes associated with woody plant expansion in the top 0–15 cm of soil. We found total soil C increased across the chronosequence from grassland (5,070 ± 250 g C m−2) to woodland (6,370 ± 390 g C m−2) ( P < 0.05) at 0–15 cm soil depth. Total soil N also increased from grassland to woodland (425 ± 16 to 556 ± 30 g N m−2) ( P < 0.05) at 0–15 cm soil depth. Coarse particulate organic matter C and N increased from grassland to woodland (940 ± 100 to 598 ± 35 g C m−2, 70 ± 10 to 35 ± 1 g N m−2) at 0–5 cm soil depth. At the ecosystem-level, we estimate C and N accumulations at 0–15 cm soil depth are occurring at a rate of 18 and 1.7 g m−2 year-1, respectively. Results of this study suggest soil resources, namely soil C and N, in the northern Great Plains are changing following woody plant expansion. [ABSTRACT FROM AUTHOR]

A major limitation to building credible soil carbon sequestration programs is the cost of measuring soil carbon change. Diffuse reflectance spectroscopy (DRS) is considered a viable low-cost alternative to traditional laboratory analysis of soil organic carbon (SOC). While numerous studies have shown that DRS can produce accurate and precise estimates of SOC across landscapes, whether DRS can detect subtle management induced changes in SOC at a given site has not been resolved. Here, we leverage archived soil samples from seven long-term research trials in the U.S. to test this question using mid infrared (MIR) spectroscopy coupled with the USDA-NRCS Kellogg Soil Survey Laboratory MIR spectral library. Overall, MIR-based estimates of SOC%, with samples scanned on a secondary instrument, were excellent with the root mean square error ranging from 0.10 to 0.33% across the seven sites. In all but two instances, the same statistically significant (p < 0.10) management effect was found using both the lab-based SOC% and MIR estimated SOC% data. Despite some additional uncertainty, primarily in the form of bias, these results suggest that large existing MIR spectral libraries can be operationalized in other laboratories for successful carbon monitoring. [ABSTRACT FROM AUTHOR]

A global, unified dataset on Soil Organic Carbon (SOC) changes under perennial crops has not existed till now. We present a global, harmonised database on SOC change resulting from perennial crop cultivation. It contains information about 1605 paired-comparison empirical values (some of which are aggregated data) from 180 different peer-reviewed studies, 709 sites, on 58 different perennial crop types, from 32 countries in temperate, tropical and boreal areas; including species used for food, bioenergy and bio-products. The database also contains information on climate, soil characteristics, management and topography. This is the first such global compilation and will act as a baseline for SOC changes in perennial crops. It will be key to supporting global modelling of land use and carbon cycle feedbacks, and supporting agricultural policy development. Design Type(s) data integration objective • data collection and processing objective • factorial design Measurement Type(s) amount of carbon atom in soil Technology Type(s) digital curation Factor Type(s) climate • Species • experimental condition • age Sample Characteristic(s) Brazil • cultivated environment • Canada • United States of America • New Zealand • Italy • Germany • Cameroon • India • Sri Lanka • Venezuela • Kingdom of Denmark • Republic of Ireland • French Republic • United Kingdom • Kingdom of Spain • Costa Rica • Ethiopia • Ghana • Indonesia • Mexico • Nigeria • Republic of South Africa • Portuguese Republic • China • Malaysia • Turkey • Israel • Sweden • italy • Georgia • Puerto Rico • Tanzania • Australia Machine-accessible metadata file describing the reported data (ISA-Tab format) [ABSTRACT FROM AUTHOR]