Caragana korshinskii Kom. plantation reduced soil aggregate stability and aggregate-associated organic carbon on desert steppe.

BACKGROUND: After implementing of the "Grain-for-Green" project, Caragana korshinskii Kom. has been widely planted in China's arid regions. Although natural restoration grassland and artificial Caragana plantations measures have long been focuses in carbon research, the combined influence of natural restoration grassland and artificial Caragana plantation measures on aggregate stability and the aggregate-associated organic carbon (OC) remains unclear. METHOD: We selected natural grassland (NG) and three different densities of Caragana plantations (high planting density, HG; middle planting density, MD; low planting density, LD) on desert steppe. The soil aggregate distribution and stability index such as fractal dimension (D), mean weight diameter (MWD), geometric mean diameter (GMD), percentage of aggregation destruction (PAD), as well as aggregate-associated OC concentration and stock were measured. RESULTS: Results shows that the soil aggregates were primarily macroaggregates (>2 mm) and mesoaggregates (0.25-2 mm) under dry sieving while microaggregates (<0.25 mm) were preponderant under wet sieving (more than 57%). Overall, compared with Caragana plantations, the MWD (4.43 and 4.51 mm) and GMD (1.72 and 1.83 mm) were both highest in two soil layers under the NG and the D (2.77 and 2.71) was lowest. Compared with the NG, the aggregate-associated OC stocks in the 0-40 cm depths in the LD, MD, and HD decreased by 41.54%, 46.93%, and 42.03%, respectively. SOC stock was mainly concentrated in the soil aggregate with sizes of >2 mm and <0.25 mm. These results suggested that natural grassland restoration measures could improve the soil aggregate stability and aggregate-associated OC concentration better than Caragana plantation restoration measures, which NG may be optimal for increasing carbon sequestration and stabilizing soil aggregates on desert steppe.

Biochar impacts on soil chemical properties, greenhouse gas emissions and forage productivity: A field experiment.

Biochar is a promising alternative to agricultural productivity and climate change mitigation. However, quantitative data are needed to better understand the productivity and greenhouse gas (GHG) emissions from agricultural fields amended with biochar. To assess the impacts of the four biochars on soil properties, forage productivity, and GHG emissions, a 1-year field experiment was conducted in a Humic Haploxerands (Andisol). Three manure-derived biochars and one wood residue biochar (all pyrolyzed at 550 °C) were applied at rates of 1% (equivalent to 11 t ha-1) in two parallel and independent experiments. The changes in (i) soil chemical properties and yield of Sorghum sudangrass (S. bicolor×S. bicolor var. Sudanese) and (ii) soil CO2 and N2O emissions were monitored. Two controls, with and without NPK, were included. The added amendments produced from residues of poultry and pig systems increased soil pH by 0.73 and 0.19 units, respectively. Increased sorghum yield were associated with fertilizer and the liming potential of the added biochar. Soil total carbon (TC) increased with the addition of different biochars, especially during the wood biochar treatment. Biochar application, regardless of the feedstock, had no significant impact on the cumulative soil CO2 emitted after a year. Soil N2O fluxes decreased (23%-50%) in treatments containing biochars with low mineral N contents and high C stability (i.e., low H:OC and Cox:TC ratios). NPK treatment resulted in the highest N2O emissions. Wood residue-derived biochar has a great potential in mitigating climate change, reducing soil N2O emissions, and promoting soil C storage. Manure-derived biochars could be instrumental in circular economy livestock systems, where pyrolyzed animal manure can satisfy the demand for nutrients and/or liming of Andisols under sustainable forage models.

Full inversion tillage during pasture renewal to increase soil carbon storage: New Zealand as a case study.

As soils under permanent pasture and grasslands have large topsoil carbon (C) stocks, the scope to sequester additional C may be limited. However, because C in pasture/grassland soils declines with depth, there may be potential to sequester additional C in the subsoil. Data from 247 continuous pasture sites in New Zealand (representing five major soil Orders and ~80% of the grassland area) showed that, on average, the 0.15-0.30 m layer contained 25-34 t ha-1 less C than the top 0.15 m. High-production grazed pastures require periodic renewal (re-seeding) every 7-14 years to maintain productivity. Our objective was to assess whether a one-time pasture renewal, involving full inversion tillage (FIT) to a depth of 0.30 m, has potential to increase C storage by burying C-rich topsoil and bringing low-C subsoil to the surface where C inputs from pasture production are greatest. Data from the 247 pasture sites were used to model changes in C stocks following FIT pasture renewal by predicting (1) the C accumulation in the new 0-0.15 m layer and (2) the decomposition of buried-C in the new 0.15-0.30 m layer. In the 20 years following FIT pasture renewal, soil C was predicted to increase by an average of 7.3-10.3 (Sedimentary soils) and 9.6-12.7 t C ha-1 (Allophanic soils), depending on the assumptions applied. Adoption of FIT for pasture renewal across all suitable soils (2.0-2.6 M ha) in New Zealand was predicted to sequester ~20-36 Mt C, sufficient to offset 9.6-17.5% of the country's cumulative greenhouse gas emissions from agriculture over 20 years at the current rate of emissions. Given that grasslands account for ~70% of global agricultural land, FIT renewal of pastures or grassland could offer a significant opportunity to sequester soil C and offset greenhouse gas emissions.

Data on the organic matter characteristics of New Zealand soils under different land uses.

This article contains data related to the research article entitled "An Investigation of Organic Matter Quality and Quantity in Acid Soils as Influenced by Soil Type and Land Use" (Shen et al., 2018) [1]. The data was collected using a chemical fractionation scheme of soil organic matter (OM). This involved the separation of organic carbon (OC) fractions based on their solubility in (i) cold and hot water, (ii) 0.1 M sodium pyrophosphate (pH ~ 10), and (iii) 2% HF solution, and the residue remaining after the HF extraction. The OM in this residue, after treatment with 2% HF solution, was characterised using pyrolysis (Py)-GC/MS. This technique involves thermal decomposition of OM into various pyrolysis products, which are then chromatographically separated and determined by mass spectroscopy. This technique has been used to semi-quantify individual soil OM constituents so that in-depth information on soil OM molecular fingerprints is provided. This article presents a detailed dataset of physical-chemical characterization, OC fractions and OM molecular fingerprints of 62 soil samples for a range of soil orders (i.e., Allophanic, Brown, Gley, Pallic and Recent) and land uses (i.e., permanently grazed pasture, ungrazed/unmanaged grasslands, annual cropping) across New Zealand. Principal component analysis was used to investigate the relationships of different soil properties with OC fractions and OM chemistry so that the underlying mechanisms responsible for the differences encountered in OM quantity and quality between soil orders and land uses are understood.

Soil carbon sequestration potential of permanent pasture and continuous cropping soils in New Zealand.

Understanding soil organic carbon (SOC) sequestration is important to develop strategies to increase the SOC stock and, thereby, offset some of the increases in atmospheric carbon dioxide. Although the capacity of soils to store SOC in a stable form is commonly attributed to the fine (clay + fine silt) fraction, the properties of the fine fraction that determine the SOC stabilization capacity are poorly known. The aim of this study was to develop an improved model to estimate the SOC stabilization capacity of Allophanic (Andisols) and non-Allophanic topsoils (0-15 cm) and, as a case study, to apply the model to predict the sequestration potential of pastoral soils across New Zealand. A quantile (90th) regression model, based on the specific surface area and extractable aluminium (pyrophosphate) content of soils, provided the best prediction of the upper limit of fine fraction carbon (FFC) (i.e. the stabilization capacity), but with different coefficients for Allophanic and non-Allophanic soils. The carbon (C) saturation deficit was estimated as the difference between the stabilization capacity of individual soils and their current C concentration. For long-term pastures, the mean saturation deficit of Allophanic soils (20.3 mg C g-1 ) was greater than that of non-Allophanic soils (16.3 mg C g-1 ). The saturation deficit of cropped soils was 1.14-1.89 times that of pasture soils. The sequestration potential of pasture soils ranged from 10 t C ha-1 (Ultic soils) to 42 t C ha-1 (Melanic soils). Although meeting the estimated national soil C sequestration potential (124 Mt C) is unrealistic, improved management practices targeted to those soils with the greatest sequestration potential could contribute significantly to off-setting New Zealand's greenhouse gas emissions. As the first national-scale estimate of SOC sequestration potential that encompasses both Allophanic and non-Allophanic soils, this serves as an informative case study for the international community.

Toward the Standardization of Biochar Analysis: The COST Action TD1107 Interlaboratory Comparison.

Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical-chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future.