Harvesting benefits: Exploring the effects of second‐best policies on enhancing soil organic carbon stocks in agriculture

Soil Organic Carbon (SOC) dynamics study in arable land use at different agro-ecological zones is important for recommendation of sustainable land use management practices against detrimental practices. This will provide insight on how to enhance SOC sequestration, improve soil quality and mitigate impact of climate change in different agro-ecological zones. This study was conducted at two agro-ecological zones of Nigeria; upland rainforest (Ado-Ekiti) and southern guinea savanna (Kabba) to evaluate SOC sequestration under arable land use. From the two agro-ecological zones, 1 ha (ha) of land was marked out, five soil samples were randomly collected at four different depths (0–15, 15–30, 30–45, and 45–60 cm) for SOC sequestration study. Higher SOC concentration and stock were observed at Ado-Ekiti site over Kabba site was due to best soil management practices like soil organic and inorganic fertilizers application and incorporation of crop residues. SOC concentration distribution varied greatly (%CV > 35%) and decreased with depth at the two agro-ecological zones. SOC stocks ranged from 6.59 t ha −1 to 24.97 t ha −1 and decreased with depth in similar trend with SOC concentration. Generally, at both sites, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) decrease with increasing depth especially to 45 cm depth while soil pH increase with increasing depth. Both SOC concentration and stock were observed to have significant positive correlation ( P < 0.01; P < 0.05) with SOM ( r = 1.000** and 0.996**; and r = 0.991** and 0.707**) and TN ( r = 0.936** and 0.934**; and r = 0.992** and 0.691**) at Ado-Ekiti and Kabba sites respectively. This indicated that increase in SOM and TN were associated with increase in SOC stock and concentration. Maximum value (20.33%) of exchangeable sodium percentage (ESP) of above critical value of 15% was recorded at Ado-Ekiti site which requires that soil be managed against sodicity. There was significant difference ( t = 2.975**) between the overall mean SOC stocks (14.83 and 9.15 t ha −1 at Ado-Ekiti and Kabba sites respectively) at two agro-ecological zones. Thus, adoption of better soil management practices will enhance SOC sequestration and soil quality at the two agro-ecological zones.

Increasing soil organic carbon (SOC) stocks in grasslands is a promising strategy for offsetting greenhouse gas (GHG) emissions from cattle ranching. Previous studies have shown that certain Urochloa grasses develop an extensive deep rooting system that contributes to higher SOC accumulation in acidic soils with low fertility and aluminum toxicity. At the Alliance Bioversity and CIAT, genetically diverse a Urochloa grasses are utilized in breeding programs aimed at developing hybrids with improved adaptation to biotic (e.g., spittlebug) and abiotic (acidic soils, aluminum toxicity, drought, and waterlogging) stresses, enhanced nutritional quality, and reduced nitrous oxide from soil and methane from cattle. However, the capacity for SOC accumulation from their deep rooting ability has not yet been considered as a target trait within these breeding programs. Since these improved grasses are pivotal for sustainable livestock intensification, this study aims to evaluate the differences in the contribution of nine Urochloa genotypes to increase SOC stocks in a Mollisol of Valle del Cauca, Colombia. The field trial was established in 2016 with the planting of nine Urochloa genotypes: four cultivars/accessions (U. brizantha cv. Marandu, U. humidicola cv. Tully, U. humidicola CIAT 26146, and U. humidicola CIAT 16888), and five hybrids (cv. Mulato II, Uh08 675, Uh08 1149, Uh 72, and Uh 91) as well as a control treatment with bare soil. Each genotype was planted in 20 x 20 m plots with three replicates, and three control plots were maintained as bare soil. Six years after establishment (early 2023), soil samples were collected from each plot at four depths (0-10, 10-20, 20-60, 60-100 cm) to estimate SOC stocks using the values of SOC concentration and bulk density. We observed that SOC concentrations decreased with depth. In grass-covered plots, the average SOC concentration was 2.17% in the surface layer (0–10 cm) and 0.25% in the deeper layer (60–100 cm). In contrast, in bare soil plots, the average SOC concentration was 1.7% in the surface layer and 0.11% in the deeper layer. Results on the stocks of SOC (0-100 cm soil depth), based on equivalent soil mass, indicated that after 6 years of establishment, plots planted with Urochloa grasses showed an average value of 127.4 Mg C ha⁻¹, which is 47% more compared to 86.4 Mg C ha⁻¹ found in bare soil. We observed a clear trend with Urochloa hybrids showing a greater ability to increase SOC stocks, in the following order: Uh 91 &gt; Uh 72 &gt; Uh08 675 &gt; cv. Marandu &gt; Uh08 1149 &gt; cv. Mulato &gt; CIAT 26146 &gt; CIAT 16888 &gt; cv. Tully. For example, the Urochloa hybrid of Uh 91 had a SOC stock of 155.66 Mg C ha⁻¹, while cv. Tully had 97.17 Mg C ha⁻¹. These results highlight the potential of Urochloa grass hybrids to contribute towards mitigation of climate change. On-going Urochloa grass breeding programs should consider incorporating the trait of SOC accumulation ability together with other desirable traits of stress resistance, improved nutritional quality, and reduced GHG emissions.

Enhancing soil organic carbon (SOC) stocks through fertilization and crop rotation will contribute to sustaining crop productivity and mitigating global warming.&amp;#160;Although it is known that cropping systems may affect SOC stocks by influencing the balance between C input and C decomposition, only few studies focused on the impact of different rice cropping systems on SOC stock changes in paddy soils.&amp;#160;In this study, we analyzed the differences in SOC stocks and their driving factors in the topsoil (0&amp;#8211;20 cm) with various fertilization measures in two rice-based cropping systems (i.e. rice-wheat rotation and double rice rotation systems) over the last four decades from seven long-term experiments in the Yangtze River catchment. The treatments include no fertilizer application (CK), application of chemical nitrogen, phosphorus and potassium fertilizers (NPK) and a combination of NPK and manure (NPKM). Results showed that during the last four decades, the topsoil SOC stock significantly increased by 8.6 t ha-1&amp;#160;on average under NPKM treatment in rice-wheat system and by 2.5&amp;#8211;6.4 t ha-1&amp;#160;on average under NPK and NPKM treatments in double rice system as compared with CK. A higher SOC sequestration rate and a longer SOC sequestration duration were found in NPKM treatment than that in NPK treatment in both cropping systems. The highest relative SOC stock percentage (SOC stock in fertilized treatments to CK) was observed under the NPKM treatment in both cropping systems, though no significant difference was found between these two cropping systems. However, the fertilization-induced relative increase of the SOC stock was 109.5% and 45.8% under the NPK and NPKM treatments, respectively in the rice-wheat system than that in the double rice system. This indicates that the rice-wheat system is more conducive for SOC sequestration. RF and SEM analyses revealed that the magnitude and influencing factors driving SOC sequestration varied between two systems. In the double rice system, continuous flooding weakens the influence of precipitation on SOC sequestration and highlights the importance of soil properties and C input. In contrast, soil properties, C input and climate factors all have important impacts on SOC sequestration in rice-wheat system. This study reveals that the rice-wheat system is more favorable for SOC sequestration despite its lower C input compared to the double rice system in China&amp;#8217;s paddies.

Abstract. We use a soil carbon (C) model (RothC), driven by a range of climate models for a range of climate scenarios to examine the impacts of future climate on global soil organic carbon (SOC) stocks. The results suggest an overall global increase in SOC stocks by 2100 under all scenarios, but with a different extent of increase among the climate model and emissions scenarios. The impacts of projected land use changes are also simulated, but have relatively minor impacts at the global scale. Whether soils gain or lose SOC depends upon the balance between C inputs and decomposition. Changes in net primary production (NPP) change C inputs to the soil, whilst decomposition usually increases under warmer temperatures, but can also be slowed by decreased soil moisture. Underlying the global trend of increasing SOC under future climate is a complex pattern of regional SOC change. SOC losses are projected to occur in northern latitudes where higher SOC decomposition rates due to higher temperatures are not balanced by increased NPP, whereas in tropical regions, NPP increases override losses due to higher SOC decomposition. The spatial heterogeneity in the response of SOC to changing climate shows how delicately balanced the competing gain and loss processes are, with subtle changes in temperature, moisture, soil type and land use, interacting to determine whether SOC increases or decreases in the future. Our results suggest that we should stop looking for a single answer regarding whether SOC stocks will increase or decrease under future climate, since there is no single answer. Instead, we should focus on improving our prediction of the factors that determine the size and direction of change, and the land management practices that can be implemented to protect and enhance SOC stocks.

Agricultural operations such as excessive tillage and intense cropping deplete soil organic carbon (SOC), making sustainable agriculture management critical for reducing greenhouse gas (GHG) emissions. This study evaluates the impact of crop intensification on soil quality and soil organic carbon stocks (SOCS) under double cropping (DC) and single cropping pattern (SC) in upper Haramosh of Gilgit, Pakistan. Soil samples were taken from cropping zones (DC and SC) under three depths (0–20, 20–40, and 40–60 cm). Standard methods were used to analyze selected soil quality parameters and SOC. Statistical analysis using ANOVA showed that soil temperature, moisture, pH, SOC, and SOCS highly significantly differed (p < 0.001) for different cropping patterns (DC and SC), whereas bulk density (BD), electrical conductivity (EC), and clay were not significantly different. The SC retained 4.4% more moisture and had lower BD than the DC, while BD increased with increasing depth. The texture of the soil was sandy loam at both cropping zones. The mean SOC and SOCS of SC were greater (by 12%) than in the DC zone. Pearson correlation showed a significant and positive correlation of SOC stock with SOC, moisture (p < 0.01), and EC (p < 0.05), but had a negative correlation with bulk density, pH (p < 0.01), and sand (p < 0.05). DC apparently degraded soil quality and organic carbon reserves, thus reducing the soil health in mountain agriculture.

Impacts of land use and biophysical properties on soil carbon stocks in southern Yunnan, China

Enhancing soil organic carbon (SOC) stocks through fertilization and crop rotation will contribute to sustaining crop productivity and mitigating global warming. In this study, we analyzed the differences in total SOC stocks and their driving factors in the topsoil (0–20 cm) with various fertilization measures in two puddled lowland rice-based cropping systems (i.e., rice-wheat rotation and double rice rotation systems) over the last four decades from seven long-term experiments in the Yangtze River catchment. The soil types include Cambisol, Luvisol, and Anthrosol. The treatments include no fertilizer application (CK), application of chemical nitrogen, phosphorus and potassium fertilizers (NPK) and a combination of NPK and manure applications (NPKM). Every year, field was ploughed to a depth of 15–20 cm before wheat sowing and rice transplanting. Residue was removed after plant harvesting. Results showed that during the last four decades, the average crop grain yield ranged from 1,151 ± 504 kg ha−1 yr−1 under CK treatment to 7,553 ± 1,373 kg ha−1 yr−1 under NPKM treatment. The topsoil SOC stock significantly increased by 8.6 t ha−1 on average under NPKM treatment in rice-wheat system and by 2.5–6.4 t ha−1 on average under NPK and NPKM treatments in double rice system as compared with CK. A higher SOC sequestration rate and a longer SOC sequestration duration were found in NPKM treatment than that in NPK treatment in both cropping systems. The highest SOC stock ratio (SOC stock in fertilizer treatments to CK) was observed under the NPKM treatment in both cropping systems, though no significant difference was found between these two cropping systems. However, the fertilization-induced relative increase of the SOC stock was 109.5% and 45.8% under the NPK and NPKM treatments, respectively in the rice-wheat system than that in the double rice system. This indicates that the rice-wheat system is more conducive for SOC sequestration. RF and SEM analyses revealed that the magnitude and influencing factors driving SOC sequestration varied between two systems. In the double rice system, continuous flooding weakens the influence of precipitation on SOC sequestration and highlights the importance of soil properties and C input. In contrast, soil properties, C input and climate factors all have important impacts on SOC sequestration in rice-wheat system. This study reveals that the rice-wheat system is more favorable for SOC sequestration despite its lower C input compared to the double rice system in China’s paddies.

A farm level approach to explore farm gross margin effects of soil organic carbon management

Post-farming land restoration schemes exhibit higher soil aggregate stability and organic carbon: Evidence in the Three Gorges Reservoir Area, China

In their paper "Unrecognized threat to global soil carbon by a widespread invasive species" O'Bryan et al. (2021) suggested that wild boar (also named feral pigs or wild pigs) and their grubbing reduce global soil organic carbon (SOC) stocks. In this study models were used to estimate global wild boar abundance and postulated additional CO2 emissions due to wild boar bioturbation. However, the authors ignored experimental evidence about the effects of wild boar on SOC that points in a completely different direction altogether.

Effects of enhancing soil organic carbon sequestration in the topsoil by fertilization on crop productivity and stability: Evidence from long-term experiments with wheat-maize cropping systems in China

Changes in soil organic and inorganic carbon stocks in deep profiles following cropland abandonment along a precipitation gradient across the Loess Plateau of China

Soil organic and inorganic carbon interactions under tillage and cover cropping determine potential for carbon accumulation in temperate, calcareous soils

BackgroundLand degradation is a treat for natural resources in Tigray high lands of northern Ethiopia, where 30–50 percent of the soil productive capacity has been lost in the past 500 years. Restoration and management of degraded lands improve soil health through enhancing soil organic carbon (SOC) stock and microbial biomass carbon (MBC). The knowledge on SOC and MBC concentration and distribution is essential to refine soil management, thereby restoring the ecosystem. This paper quantified the effect of decades old community-based soil and water conservation (SWC) measures, mainly stone terraces, exclosure with and without stone terraces, and non-conserved communal grazing lands on the distribution of MBC and SOC stock.MethodsSoil sample collection was carried out using systematic sampling design. Transects parallel to each other and to the slope of the landscape were established. In each transect, three landscape positions (i.e., upper, middle, and foot slope) were formed. Composite soil samples were taken from four corners and center of 10 m × 10 m plot of each slope positions under the different SWC measures. Analysis of variance was used to determine the difference in SOC and MBC using SAS 9.2.ResultsTotal soil organic carbon concentration was significantly higher in exclosures as compared to terraces and non-conserved grazing lands. The highest mean value of SOC stock (29 Mg C ha−1) was recorded in exclosures with terraces followed by exclosures without terraces (24 Mg C ha−1) and terraces (21 Mg C ha−1), while the lowest (16 Mg C ha−1) was recorded in non-conserved communal grazing lands. Exclosures with terraces improved SOC stock by 64%, followed by exclosures without terraces by 37%, while terraces improved the SOC stock by 25% compared to non-conserved open communal grazing lands in the last 20 years. The upper (0–15 cm) soil depth had significantly (P < 0.05) higher (24 Mg C ha−1) SOC stock than the lower (15–30 cm) soil depth (20 Mg C ha−1). Microbial biomass carbon was the highest (640 mg kg−1 soil) in exclosures without terraces, followed by exclosures with terraces, (570 mg kg−1 soil), terraces (440 mg kg−1 soil), and non-conserved communal grazing lands (370 mg kg−1 soil).ConclusionExclosures supported with terraces improved and restored the SOC stock and microbial biomass carbon of degraded free grazing lands in the highlands.

This paper focuses on the economic trade-off space between effects on yield and input costs of management measures aimed at enhancing soil organic carbon (SOC) stocks to maintain soil fertility while providing important ecosystem services. An optimising dynamic farm level model, ScotFarm, was used to investigate the financial impacts of 4 SOC management measures (cover crops, zero tillage, minimum tillage and residue management) for three groups of Scottish crop farms. A sensitivity analysis was carried out to test the robustness of the model results on crop yields and costs of production for each measure. The results suggest that financially, tillage management is the only positive measure for Scottish farms at baseline levels of yield effects and input costs. Residue management is expected to have a negative impact on farm margins for the farms. The projected maximum positive financial impact was less than 10%. Results of the sensitivity analysis indicate that financial impacts of SOC management measures on farm margins are more sensitive to a change in crop yields than to changes in input costs. The findings point to further research needs with respect to the investigated trade-off space, and have implications for agricultural policy design aimed at enhancing SOC stocks under a changing climate.