Diversified crop rotations and organic amendments as strategies for increasing soil carbon storage and stabilisation in UK arable systems

Adaptations in crop rotation with the inclusion of temporary grass-clover leys and organic amendments, have been promoted as effective ways to improve soil carbon (C) sequestration and mitigate climate change in agricultural systems. However, there are still a lot of uncertainties related to i) the combined effects of different crop rotations and different fertilisation sources, e.g., organic amendments, on soil C stocks; and ii) their potential effect on C stabilisation. The objective of this study was to evaluate the effect of different arable crop rotations with varying degrees of diversity in crop type and lengths of grass-clover ley periods and fertilisation sources on soil C stocks and C stabilisation down to 0.60 m soil depth. This was investigated in a long-term factorial field experiment-combining different crop rotation (cereal-intensive conventional vs. diversified legume-intensive organic) with different lengths of grass-clover ley periods (2 vs. 3 years), fertilisation sources (mineral vs. compost), and years (samples taken at the beginning and at the last year of one complete cycle of rotation; 8 years apart)-to explore their individual and interactive effect on soil C stock and C stabilisation at two soil depths (0–0.30 and 0.30–0.60 m). Soil C stabilisation was assessed using a unique combination of three different techniques: physical fractionation for separation of C associated to organic and mineral fractions, thermal analysis combined with differential scanning calorimetry and a quadrupole mass spectrometry (TG-DSC-QMS) for physical-chemical aspects, and pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) for molecular structural information. The findings showed higher soil C stocks under the diversified organic rotation with 3 years of grass-clover ley period at both soil depths, regardless of the fertilisation source or sampling year. However, the organic rotation seemed to deliver stable soil C stocks only in the subsoil layer. Compost fertilisation, in turn, increased topsoil C stocks between the two sample dates under both rotations, and it appears to be stable. These results suggested that combining a diversified organic rotation with 3 years grass-clover ley with compost fertilisation could be one way for agricultural systems to deliver stable soil C sequestration

Grazed temporary grass-clover leys in crop rotations can have a positive impact on soil quality under both conventional and organic agricultural systems

Soil quality (SQ) is the ability of soil to provide ecosystem functions and services. Implementation of a certain agricultural system can affect SQ and therefore play an essential role in achieving sustainable agriculture. The aim of this study was to explore how agricultural systems (conventional vs. organic), grazing regime (non-grazed vs. grazed) and the different proportions of temporary grass-clover leys in crop rotations (ley time proportion, LTP) affect SQ within a mixed (cropping and pasture/dairy system) commercial farming enterprise in the UK. Seven SQ indicators were evaluated, including chemical (pH; available phosphorus (P); potassium (K)), physical (bulk density, BD; aggregate stability, AS) and biological (total carbon (C); microbial biomass carbon, MBC) sectors. All SQ indicators were measured at three depth intervals (0-0.15, 0.15-0.30, 0.30-0.60 m), except for AS and MBC, which were only considered for the top-soil (0-0.15 m). The findings reflected existing knowledge on the advantages of organic vs. conventional systems for SQ indicators, with the former showing higher MBC and similar K, BD, AS and C in the 0-0.30-m compared to the latter. Lower topsoil available P in organic systems can be related to the lack of measurements in all P pools. When grazing was included: (a) both agricultural systems showed higher topsoil available P, C and MBC; and (b) there was a higher topsoil K in organic systems, whereas it positively affected topsoil BD and C (0.15-0.30 m) in conventional systems. Increasing LTP to 30-40% of the full crop rotation increased topsoil AS and C (0-0.30 m) in a linear fashion. Subsoil conditions (>0.30 m) favoured K, BD and C in conventional systems, but these results should be considered carefully. It was concluded that both organic and conventional systems delivered similar levels of SQ and that reviving mixed farming systems may be a key factor for delivering multifunctional agroecosystems that maintain SQ and optimize ecosystem services

Effects of integrating grass‐clover leys with livestock into arable crop rotations on soil carbon stocks and particulate and mineral‐associated soil organic matter fractions in conventional and organic systems

International audienceOrganic systems, integrated crop-livestock systems (ICL) and leys are posited as strategies to increase soil carbon (C) stocks. However, previous studies have: i) only considered one driver of change; ii) evaluated soil C content instead of stocks; iii) been limited to the 0.20 m depth; iv) used short-term leys; and v) rarely assessed the distribution of C among soil organic matter (SOM) fractions, which relates to C stabilisation. The aim of this study was to investigate the impact of conventional vs. organic agricultural systems, grazing regimes (non-grazed vs. grazed) and different proportions of temporary grass-clover leys in crop rotations (ley time proportion-LTP) on soil C stocks and C distribution among SOM fractions down to 0.60 m soil depth. SOM fractions assessed were particulate organic matter (POM>53 μm), heavy fraction (HF>53 μm) and mineral-associated silt and clay fraction (SC<53 μm). There were no differences in soil C stocks between the conventional and the organic system, but the former had higher SC-C in the 0.15 m depth. Increasing the LTP associated with livestock grazing increased: (a) soil C stocks in the topsoil (0.30 m); and (b) POM-C and HF-C in the 0.15 m and POM-C in the 0.30-0.60 m depth under both agricultural systems. The inclusion of the longer grazed grass-clover leys was especially important for topsoil POM-C and HF-C under the conventional system. These results suggest that ICL systems with increasing LTP in crop rotations can play an important role in achieving a net C benefit

Response of Ancient and Modern Wheat Varieties to Biochar Application: Effect on Hormone and Gene Expression Involved in Germination and Growth

Agriculture has changed dramatically due to mechanization, new technologies, and the increased use of chemical fertilizers. These factors maximize production and reduce food prices, but may also enhance soil degradation. Sustainable agricultural practices include altering crop varieties and the use of soil amendments to increase production, improve irrigation, and more effectively use fertilizers. Ancient and modern durum wheat varieties have been shown to be tolerant to conditions caused by climate change and increase production. Biochar soil amendments have been reported to increase crop yields, soil fertility, and to promote plant growth. However, results are variable depending on biomass source, application conditions, and crop species. This study evaluates the crop response of two contrasting durum wheat varieties on an Eutric Cambisol amended with beech wood biochar. Wheat varieties used are Saragolla, an ancient variety traditionally used in Southern Italy, and Svevo, a widely used commercial variety. The effect of biochar soil amendment on the expression of genes involved in the germination of these two varieties of wheat was determined using RT-PCR. The content of hormones such as gibberellins (GAs), auxins (IAA), and abscisic acid (ABA) was determined. Results demonstrate that biochar had a stimulatory effect on the growth performances of Svevo and Saragolla cultivars at the molecular level. This correlated to the promoted transcription of genes involved in the control of plant development. Overall, the presence of biochar as soil amendment improved the germination rates of both varieties, but the ancient wheat cultivar was better suited to the Eutric Cambisol than the commercial variety. This trend was also observed in un-amended pots, which may indicate better adaptability of the ancient wheat cultivar to withstand environmental stress than the commercial variety

Spatial analysis of influence of urban agriculture on food insecurity and stunting in Yogyakarta, Indonesia

Since 2000s there has been a renewed interest in the role urban farming plays on food security. Here we contribute to two branches of this literature: one promoting the use of geographic information systems to map urban systems and the other examining how urban farming contributes to malnutrition and stunting mitigation. We aim to produce a spatial visualization of the Yogyakarta, Indonesia urban farming system and examine the extent with which it mitigates childhood stunting the city. We conducted a survey to a sample of urban farmers where along with production and socio-economic information we collected information on the exact location of the farms. Our findings reveal a very diverse urban farming system both in terms of crops and areas of the city. Most farmers in our sample produce for auto-consumption and the majority is managed by women. The size of the farm, the use of polybags and hydroponic production technologies increase the odds of selling, while female managers decrease them. Then we investigate how urban farming mitigates childhood stunting, finding that it decreases when women manage the farm, age of farmer, number of children in the household and levels of education

Biochar properties

The search for meaningful and desirable biochar properties is still under way. Nevertheless, there are certain chemical and physical properties that are widely considered relevant to the behaviour and function of biochar in soil. In this chapter, some of the more accessible properties are described, giving the reader the necessary tools and understanding to grasp the interaction of biochar in the soil environment covered in Chapter 4

Black Carbon Contribution to Organic Carbon Stocks in Urban Soil

Soil holds 75% of the total organic carbon (TOC) stock in terrestrial ecosystems. This comprises ecosystem-derived organic carbon (OC) and black carbon (BC), a recalcitrant product of the incomplete combustion of fossil fuels and biomass. Urban topsoils are often enriched in BC from historical emissions of soot and have high TOC concentrations, but the contribution of BC to TOC throughout the urban soil profile, at a regional scale is unknown. We sampled 55 urban soil profiles across the North East of England, a region with a history of coal burning and heavy industry. Through combined elemental and thermogravimetic analyses, we found very large total soil OC stocks (31–65 kg m–2 to 1 m), exceeding typical values reported for UK woodland soils. BC contributed 28–39% of the TOC stocks, up to 23 kg C m–2 to 1 m, and was affected by soil texture. The proportional contribution of the BC-rich fraction to TOC increased with soil depth, and was enriched in topsoil under trees when compared to grassland. Our findings establish the importance of urban ecosystems in storing large amounts of OC in soils and that these soils also capture a large proportion of BC particulates emitted within urban areas

Predicting Long-Term Effects of Alternative Management Practices in Conventional and Organic Agricultural Systems on Soil Carbon Stocks Using the DayCent Model

Recently, many countries have introduced policies that promote sustainable agricultural practices, such as reducing synthetic nitrogen fertiliser and promoting diversified crop rotation. While such management changes might represent an opportunity for the agricultural sector to mitigate the impacts of climate change through carbon (C) sequestration in soils, there are still uncertainties due to the scarcity of reliable long-term data to prove this assumption. In this study, we applied the DayCent model using empirical data from a farm-scale study and an experimental trial study at Nafferton farm in the UK, to assess the long-term effects of contrasting agricultural systems (conventional vs. organic), grazing regimes (non-grazed vs. grazed), arable systems with ley phases, mineral vs. compost fertility sources and conventional vs. organic crop rotation on soil C stocks (0–0.20 m depth). The simulations showed that grazing and higher ley time proportions can increase soil C stocks for a period of at least 30 years, regardless of the agricultural system used (average increase in rates of 0.25 ± 0.02 Mg ha−1 yr−1). Compost fertiliser promoted soil C accumulation for the same period (average increase in rates of 0.3 Mg ha−1 yr−1), but its magnitude was dependent on the choice of crops in the rotation. However, ley time proportions higher than 40% of the full crop rotation did not improve soil C accumulation further. We conclude that the DayCent model can be used to identify the quantity of and the effective period for which management practices can be used to target mitigation efforts, but the balance between sustainability and productivity aspects warrants further research

Rapid Removal of Atmospheric CO₂ by Urban Soils

The measured calcium carbonate content of soils to a depth of 100 mm at a large urban development site has increased over 18 months at a rate that corresponds to the sequestration of 85 t of CO₂/ha (8.5 kg of CO₂ m^–2) annually. This is a consequence of rapid weathering of calcium silicate and hydroxide minerals derived from the demolition of concrete structures, which releases Ca that combines with CO₂ ultimately derived from the atmosphere, precipitating as calcite. Stable isotope data confirm an atmospheric origin for carbonate carbon, and ¹⁴C dating indicates the predominance of modern carbon in the pedogenic calcite. Trial pits show that carbonation extends to depths of ≥1 m. Work at other sites shows that the occurrence of pedogenic carbonates is widespread in artificially created urban soils containing Ca and Mg silicate minerals. Appropriate management of fewer than 12000 ha of urban land to maximize calcite precipitation has the potential to remove 1 million t of CO₂ from the atmosphere annually. The maximal global potential is estimated to be approximately 700–1200 Mt of CO₂ per year (representing 2.0–3.7% of total emissions from fossil fuel combustion) based on current rates of production of industry-derived Ca- and Mg-bearing materials