Short-term effects of deep ploughing on soil C stocks following renewal of a dairy pasture in New Zealand

In New Zealand’s high producing permanent pastures the topsoil constitutes a large reservoir of soil organic carbon (SOC), which shows a marked stratification with depth. As consequence, sub-surface layers can contain 10 times less carbon than the surface soil. In permanent pastures with high carbon inputs, the formation and decomposition of these surface SOC stocks are often at equilibrium and C storage shows little change over time. Pastoral based dairy systems utilising ryegrass plus clover cultivars require renewal every 7-10 years to avoid reversion to less productive grasses. This may involve spring cultivation (either no-till, shallow till or full cultivation), summer forage cropping and autumn re-grassing. It has been hypothesised that SOC stocks can be increased by inverting the soil profile at pasture renewal through infrequent (once in 25-30 years) deep mouldboard ploughing (up to 30 cm depth). Increased C sequestration occurs when the new grass quickly rebuilds SOC stocks in the new topsoil (exposed low C sub-soil) at a rate faster than the decomposition of SOC in the rich former topsoil transferred to depth (now below 15 cm). However, benefits form accelerated C storage may be offset if crop and pasture production is adversely affected by the ploughing event (e.g., as result of compaction or excessive drainage). Hence, the aim of this work was to assess the short-term effects of infrequent inversion tillage of long-term New Zealand pastoral-based dairy soils under summer crop management and autumn re-grassing. An imperfectly drained Typic Fragiaqualf under dairy grazing was deep ploughed (approx. 25 cm) and re-sown with turnip in October 2016; other treatments included were shallow (< 10 cm) cultivation and no-till. The site was core sampled (0-40 cm) before cultivation and after 5 months of turnip growth to assess changes in SOC. Plant growth, herbage quality, and nutrient leaching were monitored during the 5-month period; root growth was assessed at the end of the crop rotation. Full cultivation transferred SOC below 10 cm depth, as expected. Soil bulk density decreased whereas root mass increased (10-20 cm depth; P < 0.05) under deep cultivation only. Besides, losses of mineral N were attenuated under deep tillage, resulting in a relative increase in crop yield. The potential for infrequent inversion tillage increasing soil C sequestration as a greenhouse gas (GHG) mitigation tool is currently being tested at other sites in New Zealand

Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars

Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, δ13C and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charring- and slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biochar’s environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa

Status, sources and contamination levels of organochlorine pesticide residues in urban and agricultural areas: a preliminary review in central–southern Italian soils

Organochlorine pesticides (OCPs) are synthetic chemicals commonly used in agricultural activities to kill pests and are persistent organic pollutants (POPs). They can be detected in different environmental media, but soil is considered an important reservoir due to its retention capacity. Many different types of OCPs exist, which can have different origins and pathways in the environment. It is therefore important to study their distribution and behaviour in the environment, starting to build a picture of the potential human health risk in different contexts. This study aimed at investigating the regional distribution, possible sources and contamination levels of 24 OCP compounds in urban and rural soils from central and southern Italy. One hundred and forty-eight topsoil samples (0–20 cm top layer) from 78 urban and 70 rural areas in 11 administrative regions were collected and analysed by gas chromatography–electron capture detector (GC–ECD). Total OCP residues in soils ranged from nd (no detected) to 1043 ng/g with a mean of 29.91 ng/g and from nd to 1914 ng/g with a mean of 60.16 ng/g in urban and rural area, respectively. Endosulfan was the prevailing OCP in urban areas, followed by DDTs, Drins, Methoxychlor, HCHs, Chlordane-related compounds and HCB. In rural areas, the order of concentrations was Drins > DDTs > Methoxychlor > Endosulfans > HCHs > Chlordanes > HCB. Diagnostic ratios and robust multivariate analyses revealed that DDT in soils could be related to historical application, whilst (illegal) use of technical DDT or dicofol may still occur in some urban areas. HCH residues could be related to both historical use and recent application, whilst there was evidence that modest (yet significant) application of commercial technical HCH may still be happening in urban areas. Drins and Chlordane compounds appeared to be mostly related to historical application, whilst Endosulfan presented a complex mix of results, indicating mainly historical origin in rural areas as well as potential recent applications on urban areas. Contamination levels were quantified by Soil Quality Index (SoQI), identifying high levels in rural areas of Campania and Apulia, possibly due to the intensive nature of some agricultural practices in those regions (e.g., vineyards and olive plantations). The results from this study (which is in progress in the remaining regions of Italy) will provide an invaluable baseline for OCP distribution in Italy and a powerful argument for follow-up studies in contaminated areas. It is also hoped that similar studies will eventually constitute enough evidence to push towards an institutional response for more adequate regulation as well as a full ratification of the Stockholm Convention

Biochar: pyrogenic carbon for agricultural use: a critical review.

O biocarvão (biomassa carbonizada para uso agrícola) tem sido usado como condicionador do solo em todo o mundo, e essa tecnologia é de especial interesse para o Brasil, uma vez que tanto a ?inspiração?, que veio das Terras Pretas de Índios da Amazônia, como o fato de o Brasil ser o maior produtor mundial de carvão vegetal, com a geração de importante quantidade de resíduos na forma de finos de carvão e diversas biomassas residuais, principalmente da agroindústria, como bagaço de cana, resíduos das indústrias de madeira, papel e celulose, biocombustíveis, lodo de esgoto etc. Na última década, diversos estudos com biocarvão têm sido realizados e atualmente uma vasta literatura e excelentes revisões estão disponíveis. Objetivou-se aqui não fazer uma revisão bibliográfica exaustiva, mas sim uma revisão crítica para apontar alguns destaques na pesquisa sobre biochar. Para isso, foram selecionados alguns temaschave considerados críticos e relevantes e fez-se um ?condensado? da literatura pertinente, mais para orientar as pesquisas e tendências do que um mero olhar para o passad

Effects of full inversion tillage during pasture renewal on soil and plant cadmium concentrations: a case study in New Zealand

CAUL read and publish agreement 2023Context: Cadmium (Cd) accumulation is a concern in permanent pasture soils, as it can lead to increased Cd uptake by plants. Aims: This study aimed to quantify the effect of full inversion tillage (FIT or ploughing deeper than 30 cm), used during pasture renewal, on the redistribution of Cd within the soil profile and on plant Cd concentration. Methods: Two field trials (Trial 1, Alfisol; Trial 2, Andisol) were established in New Zealand using contrasting tillage practices (FIT; SIT, shallow tillage; and NT, no tillage) to sow turnips as summer forage crops, followed by autumn re-sowing of perennial ryegrass/white clover pasture. Key results: In the Alfisol, no measurable differences (P > 0.05) in soil and plant Cd were detected among the tillage treatments. In the Andisol, FIT decreased (P < 0.05) total (0.25 mg/kg) and extractable soil Cd (0.013 mg/kg) in the 0–5 cm depth, compared to pre-tillage (0.42 and 0.031 mg/kg, respectively). Moreover, at this soil depth, FIT achieved a 52% lower (P = 0.034) extractable soil Cd concentration than the ST treatment. In addition, the subsequent new pasture had lower (P = 0.007) average Cd concentration following FIT compared to ST (0.03 vs 0.05 mg/kg). Conclusions: We demonstrated that the use of FIT during pasture renewal is a potential solution to reduce topsoil Cd concentration. Implications: The FIT is more effective in soil where total soil Cd concentration or its degree of vertical stratification with depth is relatively high.fals

DISTRIBUTION OF CARBON IN SIZE-FRACTIONS OF A PASTURE SOIL 26 MONTHS AFTER ADDING BIOCHAR

Fractionating soils according to size and/or density of particles improves our understanding of the importance of interactions between organic and inorganic soil components on the turnover of soil organic carbon (SOC). Conventional soil physical fractionation methodologies misrepresent the contribution of pyrogenic C (e.g., biochar-derived C) to the total SOC because of the relative long turnover time of this fraction, regardless the physical SOC physical fraction in which this is found. In this study, a combination of particle size fractionation and wet sieving, as well as chemical analysis (dichromate oxidation) was tested to isolate meaningful SOC fractions in a set of 34 soils with C content ranging from 19.1–43.0 g SOC/kg soil. Topsoil and subsoil samples were obtained after 26 months of simulating cultivation at pasture renewal including pine biochar (10 t/ha) as amendment (below 10 cm depth) and growth of contrasted plant species (ryegrass vs a mixture of red clover and cocksfoot) in a lysimeter experiment using a silt loam soil (Tokomaru soil, a Pallic soil with limited drainage at depth). Across all the soils considered, the allocation of SOC in size-fractions (i.e., 2000-200, 250-53 and <53 m) was obtained by conventional wet sieving. Additionally, the total content of resistant forms of SOC (i.e.both alkyl C forms and pyrogenic C from biochar) was calculated as the sum of the dichromate-resistant C obtained in the different size-fractions. This sum of all dichromate-resistant C pools can be used as a proxy to estimate contribution of pyrogenic C to the total SOC in the soils studied. The different C fractions isolated by the appropriate combination of methodologies (particle size fractionation, wet chemistry) is proposed as an alternative to obtain the particulate, humus and resistant organic carbon fractions (POC, HOC and ROC, respectively) used in models (e.g. RothC). The developed methodology will help to improve the prediction of SOC dynamics and any impact of climate change on SOC stocks when these contain pyrogenic C.falsePalmerston North, New Zealan

PLANNING FOR CHANGES IN TOPSOIL C AND N STOCKS–SIGNIFICANCE IN C AND N BUDGETS

New Zealand has a history of rapid land use change as trends in global commodity markets influence primary sector financial sustainability. Traditionally, low sheep and beef returns accelerate extensive pastoral land use change to forest, particularly if supported by afforestation schemes (e.g.AGS and ETS). High dairy payout accelerate forest change to intensive pasture. Current debate around the agricultural sector participating in a carbon(C) economy is spreading in New Zealand, coincident with debate on de-intensification to reduce impacts on water quality. Farms including planted forest lands may be rewarded if they are able to show a decrease in nitrogen (N) loss to water and an increase in the terrestrial sink of C. While soil carbon change is not accounted for in the ETS a change from forest to pasture penalises the landowner for the reduction in biomass C with no reward or penalty for change in soil organic matter C and N. To account for soil carbon change, protocols to measure and monitor topsoil organic C and N storage at the farm level are needed. Evidence for consistent quantifiable change is required to support inclusion of soil organic matter change in both C and N accounting. Previous research in the Taupo (Central North Island) area has shown that conversion of forest land back to productive permanent pasture caused a fast accumulation of soil organic C (6.1 t C/ha/year)and of N (450kgN/ha/year) as a response to fertiliser addition and plant productivity. In this paper we provide a case study of topsoil organic matter change in a forest to pasture conversion in the Taupo region. 42 paddocks from three sites (Tainui, Tauhara and Waimana; Wairakei Estate, Taupo)were monitored in 2017. The paddocks are currently under pasture management after recent (2-11yearsago) conversion from former planted forest. Marked differences in the storage of C (38to51tC/ha15cm) and N (1.8to 3.4 t N /ha15cm; Waimana site)were detected. The relevance of these changes to C and nutrient budgeting are discussed in relation to how such large and important changes can be accounted for.falsePalmerston North, New Zealan

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

Contribution to characterisation of biochar to estimate the labile fraction of carbon

Different analytical techniques were used to find the most reliable and economic method for determining the labile fraction of C in biochar. Biochar was produced from pine, poplar and willow (PI, PO and WI, respectively) at two temperatures (400 and 550°C) and characterised using spectroscopic techniques [solid state 13C nuclear magnetic resonance spectroscopy (NMR)], molecular markers [pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS)], thermogravimetry (TG), elemental composition and wet oxidation (potassium permanganate and potassium dichromate). Short term incubation (110h) of an A horizon from an Umbrisol amended with the biochar samples at two doses (7.5 and 15tha-1) was also carried out to provide supplementary information on the influence of biochar-soil interaction on CO2 evolution. Spectroscopic analysis demonstrated that the degree of biochar carbonisation was influenced by the type of feedstock and heating conditions and followed the order WI-400<PI-400~WI-550~PO-400<PO-550<PI-550. The thermo-labile fraction of the biochar samples, estimated from TG, ranged between 21% and 49%. The fraction of total C oxidised with potassium permanganate (Cper/Ctotal) was <50gkg-1 in all cases, whereas potassium dichromate (Cdichro/Ctotal) oxidation efficiency ranged between 180 and 545gkg-1. For each type of feedstock, the highest values of either chemically or thermally degradable C corresponded to the biochar produced at low temperature. Results indicate that low cost methodologies, such as dichromate oxidation and TG, reflected the degree of biochar carbonisation, and could therefore be used to estimate the labile fraction of C in biochar. © 2011 Elsevier Ltd.The authors acknowledge financial support from the Ministry of Agriculture and Forestry of New Zealand. They would like to thank the staff of the Departmento Edafología y Química Agrícola, USC – Campus de Lugo, for the pressure plate measurements, and F. Jackson (Nutrition Laboratory, Massey University) for cellulose, hemicellulose and lignin content determination. R.C.P. was partly funded by the NZAGRC. J.A.M.-A. thanks the Spanish MCyT via the award of a Juan de la Cierva contract.Peer Reviewe