Critical carbon input to maintain current soil organic carbon stocks in global wheat systems

Feasibility of the 4 per 1000 aspirational target for soil carbon: A case study for France

Increasing soil organic carbon (SOC) stocks is a promising way to mitigate the increase in atmospheric CO₂ concentration. Based on a simple ratio between CO₂ anthropogenic emissions and SOC stocks worldwide, it has been suggested that a 0.4% (4 per 1000) yearly increase in SOC stocks could compensate for current anthropogenic CO₂ emissions. Here, we used a reverse RothC modelling approach to estimate the amount of C inputs to soils required to sustain current SOC stocks and to increase them by 4‰ per year over a period of 30 years. We assessed the feasibility of this aspirational target first by comparing the required C input with net primary productivity (NPP) flowing to the soil, and second by considering the SOC saturation concept. Calculations were performed for mainland France, at a 1 km grid cell resolution. Results showed that a 30%-40% increase in C inputs to soil would be needed to obtain a 4‰ increase per year over a 30-year period. 88.4% of cropland areas were considered unsaturated in terms of mineral-associated SOC, but characterized by a below target C balance, that is, less NPP available than required to reach the 4‰ aspirational target. Conversely, 90.4% of unimproved grasslands were characterized by an above target C balance, that is, enough NPP to reach the 4‰ objective, but 59.1% were also saturated. The situation of improved grasslands and forests was more evenly distributed among the four categories (saturated vs. unsaturated and above vs below target C balance). Future data from soil monitoring networks should enable to validate these results. Overall, our results suggest that, for mainland France, priorities should be (1) to increase NPP returns in cropland soils that are unsaturated and have a below target carbon balance and (2) to preserve SOC stocks in other land uses.

Land Cover and Land Use Change-Driven Dynamics of Soil Organic Carbon in North-East Slovakian Croplands and Grasslands Between 1970 and 2013

Soil organic carbon (SOC) in agricultural land forms part of the global terrestrial carbon cycle and it affects atmospheric carbon dioxide balance. SOC is sensitive to local agricultural management practices that sum up into regional SOC storage dynamics. Understanding regional carbon emission and sequestration trends is, therefore, important in formulating and implementing climate change adaptation and mitigation policies. In this study, the estimation of SOC stock and regional storage dynamics in the Ondavská Vrchovina region (North-Eastern Slovakia) cropland and grassland topsoil between 1970 and 2013 was performed with the RothC model and gridded spatial data on weather, initial SOC stock and historical land cover and land use changes. Initial SOC stock in the 0.3-m topsoil layer was estimated at 38.4 t ha−1 in 1970. The 2013 simulated value was 49.2 t ha−1, and the 1993–2013 simulated SOC stock values were within the measured data range. The total SOC storage in the study area, cropland and grassland areas, was 4.21 Mt in 1970 and 5.16 Mt in 2013, and this 0.95 Mt net SOC gain was attributed to inter-conversions of cropland and grassland areas between 1970 and 2013, which caused different organic carbon inputs to the soil during the simulation period with a strong effect on SOC stock temporal dynamics.

Physiological and biochemical response of wheat (Triticum aestivum) to TiO2 nanoparticles in phosphorous amended soil: A full life cycle study

Nanoparticles (NPs) application in soil as nano-fertilizers to increase crop yield is getting attention due to their higher efficiency and less environmental risks. This study investigated the interactive effects of variable titanium dioxide nanoparticles (TiO₂-NPs) levels (0, 30, 50 and 100 mg kg^-1) superimposed to phosphorus (P) fertilizer application in soil at the rates of 0, 25 and 50 mg kg^-1 on wheat crop. Physiological parameters of plants, their antioxidant enzymes activities (SOD, POD), and contents of crude protein, H₂O₂, MDA and metals/nutrients (Al, Ca, Mg, Fe, Zn and Cu) were measured. Data on physiological traits revealed that application of 50 mg kg^-1 of TiO₂-NPs without P fertilizer significantly enhanced the root and shoot length by 63 and 26%, respectively. Increased contents of nutrients in the shoots, viz., Ca (316%), Cu (296%), Al (171%) and Mg (187%) with 50 mg kg^-1 TiO₂-NPs treatment reflected improvement in crop growth and grain quality. Furthermore, P contents in plant tissues were raised up to 56% with 50 mg kg^-1 of TiO₂-NPs even in the absence of P fertilizer. In the soil, concentration of phytoavailable P was significantly increased up to 63.3% in the presence of 50 mg kg^-1 TiO₂-NPs as compared to control. Contents of crude protein in grain were also enhanced by 22.8% (at P₅₀) and 17.4% (at P₂₅) with 50 mg kg^-1 TiO₂-NPs application. Along with P application, TiO₂-NPs triggered the activities of SOD (2.06-33.97%) and POD (up to 13.19%), and H₂O₂ production (50.6-138.8%). However, MDA contents were not elevated significantly at any level of TiO₂-NPs, and remained at par with control. It was noteworthy that highest level of TiO₂-NPs, viz., 100 mg kg^-1 exhibited plant and nutrients response lower than that with 50 mg kg^-1. Further, TiO₂-NPs triggered the bioavailability of micronutrient heavy metals (Zn, Cu and Fe) and Al, which could have toxicity at higher concentrations. These results suggested that TiO₂-NPs might have some affinities with phosphate compounds and metal ions in the soil to bring them in soluble form, which enhanced their bioavailability. Although it improved the crop yield and quality, but toxic or negative impact of TiO₂-NPs was also apparent at higher dose. Therefore, investigations on the potential interactions of NPs with other nutrients and toxic metals are needed to enhance our understanding for the safer application of nano-fertilizer.

Estimating soil organic carbon stocks under commercial forestry using topo-climate variables in KwaZulu-Natal, South Africa

Commercial forests are expanding globally, with great potential to absorb carbon and mitigate climate change. However, whereas the role of natural forests in carbon sequestration has been widely investigated, there is a paucity in the literature on the role of commercial forests in carbon assimilation. Hence, understanding the role of commercial forests in carbon storage is essential for quantifying local, regional or global carbon balances, which is valuable for climate change mitigation. Soil carbon is known to be the largest pool within any forest landscape, and is controlled by a wide range of physical and climatic factors. However, the relationship between soil organic carbon (SOC) and topo-climatic variables controlling its distribution within commercial forests is still poorly understood. Due to the limitations encountered in traditional systems of SOC determination, particularly at large spatial extents, geospatial techniques have recently emerged as a viable alternative for mapping soil properties. Therefore, this study sought to map SOC stocks variability within the commercial forest landscape, using landscape topo-climatic variables. A total of 81 soil samples was analysed for SOC concentrations and 31 topographic and climatic variables were used as predictors to SOC variability. To reduce multicollinearity, these variables were reduced to 11 using stepwise backward elimination and the maximum entropy (Maxent) algorithm was used for regression analysis to determine the relationship between SOC and the selected topo-climatic variables. Good accuracies were obtained for both training (area under the curve = 0.906) and test (area under the curve = 0.885) data sets, and demonstrate the effectiveness of selected topo-climatic variables and the Maxent algorithm in predicting SOC stocks. This study provides a framework for monitoring the status of soil carbon in commercial forest compartments and provides a viable approach for local, national or regional carbon accounting – valuable for climate change mitigation.

Detailed global modelling of soil organic carbon in cropland, grassland and forest soils

Assessments of the global carbon (C) cycle typically rely on simplified models which consider large areas as homogeneous in terms of the response of soils to land use or consider very broad land classes. For example, "cropland" is typically modelled as an aggregation of distinct practices and individual crops over large regions. Here, we use the process-based Rothamsted soil Carbon Model (RothC model), which has a history of being successfully applied at a global scale, to calculate attainable SOC stocks and C mineralization rates for each of c. 17,000 regions (combination of soil type and texture, climate type, initial land use and country) in the World, under near-past climate conditions. We considered 28 individual crops and, for each, multiple production practices, plus 16 forest types and 1 grassland class (total of 80 classes). We find that conversion to cropland can result in SOC increases, particularly when the soil remains covered with crop residues (an average gain of 12 t C/ha) or using irrigation (4 t C/ha), which are mutually reinforcing effects. Attainable SOC stocks vary significantly depending on the land use class, particularly for cropland. Common aggregations in global modelling of a single agricultural class would be inaccurate representations of these results. Attainable SOC stocks obtained here were compared to long-term experiment data and are well aligned with the literature. Our results provide a regional and detailed understanding of C sequestration that will also enable better greenhouse gas reporting at national level as alternatives to IPCC tier 2 defaults.

Effects of Nanochitin on the Enhancement of the Grain Yield and Quality of Winter Wheat

This study investigated the effects of different rates of nanochitin in soil on the grain yield and quality of winter wheat. Nanochitin obtained by acidic hydrolysis of shrimp chitin was a rod-like whisker possessing a hydrodynamic diameter of 143 nm and ζ potential of 55.7 mV. Two varieties of winter wheat, multi-spike wheat (MSW) and large spike wheat (LSW), were treated with the nanochitin suspension in outside pot experiments. The results showed that 0.006 g kg^-1 of nanochitin in soil could significantly enhance the yield by 23.0% for MSW and 33.4% for LSW, with significant increases of net photosynthesis rate, stomatal conductance, intercellular CO₂ concentrations, and transpiration rate in flag leaf at the grain filling stage. Grain protein, iron, and zinc contents in wheat treated with nanochitin were also increased by 5.0, 10.3, and 22.1% for MSW and 33.4, 32.0, and 27.0% for LSW, respectively. This indicated that utilization of nanochitin has a great potential in future agriculture sustainability and crop production.

Climate Change Impacts on Yields and Soil Carbon in Row Crop Dryland Agriculture

Dryland agroecosystems could be a sizable sink for atmospheric carbon (C) due to their spatial extent and level of degradation, providing climate change mitigation. We examined productivity and soil C dynamics under two climate change scenarios (moderate warming, representative concentration pathway [RCP] 4.5; and high warming, RCP 8.5), using long-term experimental data and the DayCent process-based model for three sites with varying climates and soil conditions in the US High Plains. Each site included a no-till cropping intensity gradient introduced in 1985, with treatments ranging from wheat-fallow ( L.) to continuous annual cropping and perennial grass. Simulations were extended to 2100 using data from 16 global circulation models to estimate uncertainty. Simulated yields declined for all crops (up to 50% for wheat), with small changes after 2050 under RCP 4.5 and continued losses to 2100 under RCP 8.5. Of the cropped systems, continuous cropping had the highest average productivity and soil C sequestration rates (78.1 kg C ha yr from 2015 to 2045 under RCP 4.5). Any increase in soil C for cropped rotations was realized by 2050, but grassland treatments increased soil C (up to 69%) through 2100, even under RCP 8.5. Our simulations indicate that reduced frequency of summer fallow can both increase annualized yields and store more soil C. As evapotranspiration is likely to increase, reducing fallow periods without live vegetation from dryland agricultural rotations may enhance the resilience of these systems to climate change while also increasing soil C storage and mitigating carbon dioxide emissions.

Cropping System Conversion led to Organic Carbon Change in China's Mollisols Regions

Land use change driven by diet, globalization, and technology advancement have greatly influenced agricultural production and environment in the mollisols region of China, with a marked impact on the depletion of soil organic matter, a signature property of mollisols. Here we report findings on soil organic carbon (SOC) change in three different cropping systems (soybean, soybean/maize, corn) in Northeast China during a 10-year time span. The results indicated that the decline rate of SOC in recent ten years (0.27 g kg-1 yr-1) has slowed down considerably compared to previous decades (1.12 g kg-1 yr-1). Crop system conversion from soybean monocropping to corn monocropping or break system was the critical factor for SOC change, and the background SOC was the second influence factor. When approaching a SOC turning point, conversion from low carbon input crop system (soybeans monocropping) to high carbon input crop system helped slow down the SOC decline (break crop) or even improve SOC (corn monocropping) in mollisols regions. This result implied that imported soybean has brought benefit for Northeast China. But for sustainable goal in China's mollisols region, straw returning, optimized nitrogen fertilization and no tillage are all necessary whatever in continues maize or rotation system.

Changes in soil organic carbon in croplands subjected to fertilizer management: a global meta-analysis

Cropland soil organic carbon (SOC) is undergoing substantial alterations due to both environmental and anthropogenic changes. Although numerous case studies have been conducted, there remains a lack of quantification of the consequences of such environmental and anthropogenic changes on the SOC sequestration across global agricultural systems. Here, we conducted a global meta-analysis of SOC changes under different fertilizer managements, namely unbalanced application of chemical fertilizers (UCF), balanced application of chemical fertilizers (CF), chemical fertilizers with straw application (CFS), and chemical fertilizers with manure application (CFM). We show that topsoil organic carbon (C) increased by 0.9 (0.7-1.0, 95% confidence interval (CI)) g kg(-1) (10.0%, relative change, hereafter the same), 1.7 (1.2-2.3) g kg(-1) (15.4%), 2.0 (1.9-2.2) g kg(-1) (19.5%) and 3.5 (3.2-3.8) g kg(-1) (36.2%) under UCF, CF, CFS and CFM, respectively. The C sequestration durations were estimated as 28-73 years under CFS and 26-117 years under CFM but with high variability across climatic regions. At least 2.0 Mg ha(-1) yr(-1) C input is needed to maintain the SOC in ~85% cases. We highlight a great C sequestration potential of applying CF, and adopting CFS and CFM is highly important for either improving or maintaining current SOC stocks across all agro-ecosystems.