Soil Organic Carbon Retention Research Articles

Soil organic carbon stock and retention rate among land uses along Didessa toposequence in humid Western Ethiopia

BackgroundThere is scarcity of scientific information on stocks and retention rate of soil organic carbon (SOC) among mixed farming systems in humid Western Ethiopia. The objectives of study were to determine the SOC stocks and retention rates along a 53-km long toposequence of Didessa watershed. The study was conducted in mixed farming systems (annual arable cropping, grazing, fallow, grassland, coffee agroforestry, eucalyptus agroforestry and mechanized irrigated sugarcane production) within an elevation range of 1273 to 2543 m above sea level.ResultsThe results revealed that land use types greatly affected SOC stocks and retention rates in the upper 20 cm soil depth. The SOC stocks ranged from 9.27 to 13.5 Mg C ha−1 (0–20 cm) while the retention rates were 0.11, 0.20, 0.28, 0.31 and 1.14 Mg C ha−1 year−1 for coffee agroforestry, fallow, grazing, eucalyptus agroforestry and irrigated sugarcane production systems, respectively.ConclusionThe retention rates demonstrated that the different farming systems are potential source of C sinks. The study indicated that the farming systems are efficient in sequestering SOC and their benefits can be further adopted for their economic values, social significance, restoration of degraded land, and sequestration of carbon (C) in humid tropical Western Ethiopia.

Comparing publicly available databases to evaluate soil organic carbon in Maine, USA

AbstractElevated greenhouse gas (GHG) emissions have resulted in growing societal interest in natural climate solutions that include enhancing soil organic carbon (SOC). This study evaluated SOC from three USDA soil databases for Maine, a state that is nearly 90% forested. These databases were: (1) Forest Inventory and Analysis (FIA), (2) NRCS Soil Survey Geographic (SSURGO), and (3) Rapid Carbon Assessment (RaCA). We compared estimates of SOC density and concentration among databases and analyzed relationships between key soil properties and SOC densities and concentrations. Estimates of SOC density to a 20 cm depth which allows comparison among all three databases were 77 ± 1.2 Mg ha−1, 95 ± 0.3 Mg ha−1, and 39 ± 2.2 Mg ha−1 for SSURGO, RaCA, and FIA, respectively. Significant differences existed among databases in SOC density at shallow depth increments, and marked differences existed among databases in the soil depths measured. Analysis of the influence of soil texture and drainage class on SOC highlighted the importance of silt and clay in SOC retention. A hypothetical increase in forest and agricultural SOC was compared to reported Maine GHG emissions to illustrate potential policy implications in the use of soil databases. We conclude that all three databases are valuable but not interchangeable. The database should be carefully chosen to match the objectives of the user.

Effects of elevation and slope aspect on the distribution of the soil organic carbon associated with Al and Fe mineral phases in alpine shrub–meadow soil

Mountain ecosystems store a large amount of soil organic carbon (SOC) sensitive to global climate change. The SOC associated with Al and Fe minerals is important for SOC retention because of the ubiquitous nature and highly reactive surface properties of these minerals. Topography is also known to impact the distribution and transformation of SOC by creating different microclimates. However, the effect of topography on the distribution of organo–mineral associations has seldom been reported. This study uses a selective dissolution method to quantify the soil carbon (C) fractions associated with Al and Fe minerals in alpine shrub–meadow soil. Na-pyrophosphate (PP), HCl-hydroxylamine (HH) and dithionite-HCl (DH) were used to quantify organo–metal complexes, SOC associated with short-range order (SRO) phases and crystalline phases, respectively. Results suggest that the Al and Fe mineral-associated C accounted for a small proportion of SOC (less than 30%) in each extraction. A higher concentration coupled with a lower percentage of SOC was found in the A horizon compared to the B horizon. A significant correlation was observed between Fe and C in PP and HH extractions, whereas Al was significantly correlated with C in DH extractions. Elevation and slope aspect strongly influenced soil biotic and abiotic parameters, as well as organo–mineral associations. The C fractions extracted by PP and HH were significantly higher in the NE slope aspect than the SW slope aspect. These fractions were positively correlated with soil water content and negatively correlated with soil pH. The C fractions extracted using DH decreased with increasing elevation and were positively correlated with DH extractable Al. Our results highlight the role of topography on the distribution of organo–mineral associations, which should be considered during the assessment of SOC stability in alpine soils.

Nitrogen, water content, phosphorus and active iron jointly regulate soil organic carbon in tropical acid red soil forest

AbstractIncreasing forest soil organic carbon (SOC) storage is important for reducing carbon dioxide (CO2) emissions from terrestrial ecosystems and mitigating global climate change. Although the effects of altitude, temperature and rainfall on organic carbon have been studied extensively, it is difficult to increase SOC storage by changing these factors in actual forest management. This study determined the SOC, soil physical and chemical properties, nutrient elements, heavy metal elements, soil minerals and microbial biomass in the 0–140‐cm soil layer of the monsoon broad‐leaved forest in the acid red soil region of southwestern China by stratification. We tried to identify the soil factors affecting the SOC storage of the forest in the acid red soil region and determine the weights of the factors affecting the SOC, with the aim of improving the SOC retention capacity in forest management by changing the main soil factors affecting SOC storage. The results showed that the soil factors affecting the forest SOC storage in this area are total nitrogen (N, 22.7%) > soil water content (19.9%) > active iron (including poorly crystalline iron, Feo, 15.5%) > pH (9.5%) > phosphorus (P, 9.4%) > aluminium (Al, 8.9%) > silicon (Si, 7.1%) > sulphur (S, 6.8%). Of these factors, N, the water content, Feo, and P are practical factors for forest management, whereas the pH, Al, Si and S are not. SOC was significantly positively correlated with the soil N concentration, water content, active iron content and P concentration (p < .05). In acidic red soil areas, with active iron as the highlight, N, soil water content, phosphorus and active iron jointly regulate the forest SOC storage capacity. Consequently, in actual forest management, any measures to promote soil N and water content and to activate inactive iron can enhance the storage of SOC, as appropriate input of N and P fertiliser and irrigation in dry years and the dry season.Highlights The soil environmental factors affecting SOC storage in forest soil are quantified Activation of inactive iron helps SOC storage in forest soil Irrigation and N and P input are effective for helping SOC storage in forest soil N, WC, P and Feo jointly regulate SOC in tropical acid red soil forest

Soil parent material controls organic matter stocks and retention patterns in subtropical China

The influence of parent material on soil organic carbon (SOC) retention remains largely unstudied. Here, we aimed to reveal the role of soil parent material on SOC stocks and elucidate the underlying SOC retention patterns for soils derived from limestone, quaternary red earth, granite, basalt, and tertiary red sandstone in subtropical China. The study assessed 110 topsoils (0–20 cm) under two land uses (forest and cultivated), but with similar topography. We compared soil properties (pH, oxides, multivalent cations, texture, aggregates) and SOC stocks, total SOC concentration as well as three organic C fractions (active, slow, and passive C). Factors influencing SOC concentration were explored using a combination of stepwise multiple regression analysis and redundancy analysis. Topsoil SOC stocks and SOC concentration varied significantly among the five parent materials, with the greatest values all observed in limestone-derived soils and the lowest in tertiary red sandstone–derived soils. While parent material significantly influenced both quantity and quality of SOC, there was no land use effect on the proportion of organic C fractions. Our results have also shown that parent material mediates land use impacts on SOC. The SOC stocks and SOC concentration in limestone, quaternary red earth, and basalt-derived soils were significantly higher in forest than in arable soils, while no significant land use effect was found for soils derived on granite and tertiary red sandstone. Soil aggregates, texture, content of Fe oxides, and multivalent cations accounted for 67.8% of the variation in SOC concentration, and both SOC stocks and SOC concentration were more closely related to aggregation and soil texture. The major influencing factors for SOC retention differed with parent material, with Ca2+/Mg2+-mediated interactions between organic matter and mineral surfaces being the main regulating processes for limestone-derived soils and oxide-mediated mechanisms to form stable aggregates being the likely SOC protecting patters for quaternary red earth and basalt-derived soils. Due to the coarse texture and low aggregate stability, the soils derived from granite and tertiary red sandstone lacked the properties for SOC preservation, with pH the main predictor for SOC concentration. Macroaggregates (> 2 mm) played especially important role in shaping SOC stocks. Parent material exerts an influence on SOC stocks and retention patterns, and should be used in determining SOC storage potential for soils.

Spatial variability and dynamics of soil pH, soil organic carbon and matter content: The case of the Wonji Shoa sugarcane plantation

Abstract This study presents the spatial variability and dynamics of soil organic carbon (SOC), soil organic matter (SOM) and soil pH contents at the Wonji Shoa Sugar Estate (WSSE), Ethiopia. Soil samples were collected immediately after the sugarcane was harvested and then analysed for SOC, SOM and pH content using standard procedures. The analysis results showed that the pH value varied between 6.7–8.4 (neutral to moderately alkaline) and 7.3–8.5 (neutral to strongly alkaline) for the top and bottom soil profiles, respectively. The SOM content is in the range of 1.1–6.7% and 0.74–3.3% for the upper and lower soil layers, respectively. Nearly 45% of the samples demonstrated a SOM content below the desirable threshold (<2.1%) in the bottom layer and, hence, inadequate. Moreover, most of the topsoil layer (95%) has an SOM content exceeding the desirable limit and hence is categorized within the normal range. Interestingly, the SOC content showed a spatial variability in both the surface and sub-surface soil layers. A lower SOC and SOM content was found for the sub-soil in the south and southwestern part of the plantation. A further decline in the SOC and SOM content may face the estate if the current waterlogging condition continues in the future for a long period. Overall, the study result emphasizes the need to minimize the pre-harvest burning of sugarcane and action is needed to change the irrigation method to green harvesting to facilitate the SOC retention in the soil and minimize the greenhouse emission effect on the environment, hence improving soil quality in the long-term.

Microtopography-mediated hydrologic environment controls elemental migration and mineral weathering in subalpine surface soils of subtropical monsoonal China

Local topography and elevation gradients can exert important influences on soil formation processes such as elemental migration, mineral weathering, and soil organic matter (SOM) accumulation, yet these influences remain insufficiently investigated to date, particularly in surface soils of subtropical monsoonal regions. Here, we report on an investigation of a series of surface soils collected from four different topographic locations across the subalpine Dajiuhu Critical Zone Observatory (CZO), representing hillslope (planar), swale and river channel (convergent), and bulge (divergent) microtopographic sites. Evidence provided by rare-earth element (REE) patterns, immobile element ratios, clay-mineral compositions, and particle-size distributions suggests that these soils have rather uniform parent materials. X-ray diffraction (XRD) analysis revealed that secondary clay minerals in these soils are complex, being dominated by various interstratified clays. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy shows similar patterns among the swale, bulge, and river-channel soils that differ from those of the hillslope soils. Most soils at convergent sites with poor drainage contain more smectitic clays (interstratified illite/smectite and chlorite/smectite) and less vermiculitic clays (hydroxyl-interlayered vermiculite and interstratified illite/hydroxyl-interlayered vermiculite), and exhibit weaker chemical weathering and fewer elemental losses than those from non-convergent sites. The diversity of clay types can be ascribed to the complexity and heterogeneity, in particular of pH and hydrology, in these soil environments. Across the range of microtopographic sites investigated here, elemental migration and chemical weathering are generally coupled, with greater elemental losses associated with more intense chemical weathering. Soil organic carbon (SOC) content generally increases at higher elevations, which is attributable to lower temperatures and a consequent reduction of microbial remineralization, and under more reducing soil water conditions. Though influenced by eolian dust, variations in Fe/Mn, Ce anomaly, and Corg/P can reflect redox conditions of different soils. SOC retention is also closely associated with soil redox status, with more reducing conditions being more conducive to SOC preservation.

Impacts of biochar application on upland agriculture: A review

Soil degradation has become an emerging global problem limiting sustainable upland crop production. Soil erosion, soil acidity, low fertility, inorganic/organic contamination, and salinization challenge food security and lead to severe economic constraints. Therefore, a new research agenda to develop cost-beneficial amendments for improving upland soil quality and productivity is urgently required. Biochar has been used in recent years to mitigate the problems mentioned above. Application of biochar improves the upland soil quality through significant changes in soil physicochemical and biological properties, thereby substantially increasing crop yield. This review article aims to discuss the effects of biochar on upland soil quality and productivity based on biochar-soil interactions. The yield of various upland crops can be enhanced by biochar-induced increases of nutrient availability and topsoil retention/recovery. Furthermore, biochar can assist in controlling unsuitable soil acidity/alkalinity/salinity and remediating a contaminated soil while increasing the retention of soil organic carbon, water content, and thereby high crop yield. Biochar is strongly recommended as one of the best management practices to meet the challenges of upland agriculture. However, the properties of biochar and soil type should be considered carefully prior to application.

Soil organic carbon sequestration as influenced by long-term manuring and fertilization in the rice-wheat cropping system

Fertilization is a feasible approach to increase the soil organic carbon. To investigate the effect of fertilization on crop biomass carbon, dynamics of soil organic carbon and soil carbon sequestration rate in the (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system under the middle reach of the Yangtze River, central China, a thirty-three years (1981 − 2013) long-term fertilizer experiment was conducted with nine treatments, including no amendment addition treatment (control), nitrogen (N), phosphorus (P), potassium (K) fertilizer treatments (N, NP, NPK), manure (M) and manure combined with chemical fertilizer treatments (MN, MNP, MNPK, hMNPK). The results indicated that average crop biomass carbon was increased by 39.9 − 77.2% compared to unfertilized control (4.43 t ha−1 yr−1) due to fertilizer application, the highest crop biomass carbon was 7.85 t ha−1 yr−1 in the hMNPK treatment and the lowest crop biomass carbon was 5.21 t ha−1 yr−1 in the N alone treatment. The annual total organic carbon input were 4.14 t ha−1 yr−1 in the M treatment and 5.80 t ha−1 yr−1 in the hMNPK treatment, which was 1.95 − 2.74 times of those in the NPK treatments (2.12 t ha−1 yr−1). Total organic carbon input of soil were increased by 10.2 − 23.3 kg C ha−1 yr−1, and increment rate in the appended manure treatments were much higher than those in the control and inorganic fertilizer treatments. Soil organic carbon retention in the topsoil (0 − 20 cm) decreased by 0.11 − 0.14 t ha−1 yr−1 in the control, N and NP treatments; nevertheless, soil organic carbon sequestration rates varied from 0.03 to 0.20 t ha−1 yr−1 in the NPK and appended organic manure treatments. These results demonstrate that organic manure use or integrated organic manure with chemical fertilizer application can be important strategies for increasing soil organic carbon sequestration and maintaining soil quality in the rice-wheat cropping system of China.

A novel soil amendment for enhancing soil moisture retention and soil carbon in drought-prone soils

Crop yield reductions are common in drought-stressed agroecosystems and are likely to become more frequent with climate change. To combat this, soil amendments are often used to enhance soil moisture retention but typically only lead to marginal improvements. Moreover, even as concern over agricultural water use mounts, a large fraction of food is wasted. Diverting more food waste and byproducts back to agricultural fields could reduce waste issues while ameliorating critical water limitations. We evaluated lactobionate, a lactose derivative and major dairy industry byproduct, as a potential soil amendment for enhancing both soil moisture and soil organic carbon (SOC). Lactobionate (LB) is a hydrophilic compound consisting primarily of cations and simple sugar acids. These combined properties could synergistically modify numerous controls on soil-water balances.In a laboratory setting, we compared LB stabilized with various cations (K+, NH4+, and Ca+) across a range of soil types to determine LB effects on soil moisture and SOC retention. All LB amendments increased soil water content relative to unamended soil across a range of soil matric potentials and raised available water content by 37%. Additionally, LB amended soils had on average 70 times more microbial biomass and decreased soil inorganic nitrogen content compared to unamended soils. We found that K+-LB, the most effective amendment, increased soil water content by 100–600% compared to unamended soils and as much as 87% of the increased SOC following LB additions was retained after 2 months. Our results suggest that tapping into novel sources of organic inputs such as LB may be an effective approach for simultaneously enhancing soil moisture and carbon stocks while increasing the economic and energetic value of food production byproducts.

Canopy gaps accelerate soil organic carbon retention by soil microbial biomass in the organic horizon in a subalpine fir forest

Canopy gaps are a key component of the disturbance regime and old-growth character in subalpine coniferous forests. Despite the importance of canopy gaps in the dynamics and management of subalpine forests, limited information is available on the temporal dynamics of microbial pools and their roles in the responses of soil organic matter and nutrient flux to canopy gaps. This study tests the hypothesis that gap creation facilitates soil organic carbon (C) retention by soil microbial biomass in the organic horizon. Based on the degree of decomposition, the organic horizon can be divided into fresh litter layer (LL), fragmented litter layer (FL) and humified litter layer (HL) components; these layers represent different stages of litter decomposition. We examined the microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) from the gap center to closed canopy in a subalpine Minjiang fir (Abies faxoniana) forest during different seasons. Gap creation promoted soil organic C retention by soil microbial biomass in the organic horizon. Storage of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) accumulated in the HL. Moreover, gap creation accelerated C, nitrogen (N) and phosphorus (P) releases from the LL but inhibited C, N and P outputs from the HL. Microbial biomass in the LL responded rapidly and sensitively to canopy gaps. The most important factors affecting microbial biomass in the organic horizon were soil temperature and snow cover, which are governed by the canopy gap. Microbial pools and their stoichiometry were significantly and positively correlated with TOC. A thorough comprehension of the spatio-temporal traits of microbial biomass pools in the organic horizon under gap creation could aid the regeneration of protected subalpine fir forest on the eastern Tibetan Plateau.

Soil organic carbon retention more affected by altitude than texture in a forested mountain range in Brazil

Little is known about how soil organic carbon (SOC) under tropical forests is affected by altitude. We investigated the effects of soil texture and altitude on SOC retention under native forests in Brazil, by sampling two pairs of soils of coarser and finer texture, developed respectively from quartzite and mica-schist. One soil pair was sited at altitude 1060 m, and the other at 1230 m, along a mountain range. For 1060 m, the soil with ~36% clay contained 227 Mg SOC ha–1 (0–1 m depth), the double of the soil with ~16% clay. Such effect of texture was negligible at 1230 m, where SOC stocks were 205 Mg ha–1 for the soil with ~12% clay, and 217 Mg ha–1 for the soil with ~21% clay. Furthermore, there were positive correlations between SOC concentrations with clay + silt contents and specific surface area for 1060 m but not 1230 m altitude, suggesting that SOC retention was affected by texture only for altitudes near 1000 m or lower. At 1230 m, lower temperatures were predominant in SOC stabilisation through slower decomposition. In addition, 65–80% of total SOC was associated with clays, indicating a high degree of organic alteration. Interestingly, at 1235 m, SOC concentration in clay fractions reached 17%, much higher than at 1060 m, strongly suggesting SOC saturation. Thus, at 1235 m the interaction of SOC with soil minerals was probably weaker than at 1060 m or lower, and so SOC stocks are more susceptible to decay.

Effects of Land Use Change, Cultivation, and Landscape Position on Prairie Soil Organic Carbon Stocks

Temperate grassland soils are typically a sink for carbon. However, it is estimated that up to 99% of tallgrass prairies in North America have been converted to another land use. These conversions can lead to increased soil erosion and soil organic carbon (SOC) mineralization rates, turning a large carbon sink into a source. The purpose of this study was to compare by land use the retention of SOC, TSN, and fly ash on sloping landscapes with an emphasis on measuring the subsoil in addition to the surface soil. Eight paired plots were established on adjacent, sloping landscape profiles in western Iowa; one site a cropland and the other a remnant tallgrass prairie. The prairie landscape had a baseline SOC stock of 232 Mg-C ha-1. After roughly 150 years of agriculture the cropland had 52% less SOC, 39% less TSN, and 22% less fly ash which equates to annual losses of 0.55 Mg-C ha-1 yr-1, 0.04 Mg-N ha-1 yr-1, and 0.0002 Mg-fly ash ha-1 yr-1.

Substantial soil organic carbon retention along floodplains of mountain streams

AbstractSmall, snowmelt‐dominated mountain streams have the potential to store substantial organic carbon in floodplain sediment because of high inputs of particulate organic matter, relatively lower temperatures compared with lowland regions, and potential for increased moisture conditions. This work (i) quantifies mean soil organic carbon (OC) content along 24 study reaches in the Colorado Rocky Mountains using 660 soil samples, (ii) identifies potential controls of OC content based on soil properties and spatial position with respect to the channel, and (iii) and examines soil properties and OC across various floodplain geomorphic features in the study area. Stepwise multiple linear regression (adjusted r2 = 0.48, p < 0.001) indicates that percentage of silt and clay, sample depth, percent sand, distance from the channel, and relative elevation from the channel are significant predictors of OC content in the study area. Principle component analysis indicates limited separation between geomorphic floodplain features based on predictors of OC content. A lack of significant differences among floodplain features suggests that the systematic random sampling employed in this study can capture the variability of OC across floodplains in the study area. Mean floodplain OC (6.3 ± 0.3%) is more variable but on average greater than values in uplands (1.5 ± 0.08% to 2.2 ± 0.14%) of the Colorado Front Range and higher than published values from floodplains in other regions, particularly those of larger rivers.

Soil parent material, texture and oxide contents have little effect on soil organic carbon retention in tropical highlands

In tropical humid conditions, soil organic carbon (SOC) concentrations have been reported to be proportional to clay, clay+silt and Fe/Al oxide contents. Typically, soil texture and mineralogy are strongly dependent on soil parent materials, but it is not known if SOC retention would also be affected by soil parent material. Such relationship, if established, could be useful to estimate regional SOC stocks, since geological maps are more numerous and often more accurate than soil maps. The objective of this study was to assess the effect of parent material, texture,and oxide content on SOC contents in tropical highlands. Thus, samples to 1-m depth were obetained for seven soils derived from quartzite, sericite-schist, itabirite, serpentinite, limestone, gneiss and phyllite. All soils formed under similar climate and native forest, and were located on the midslope position. Despite wide variations in soil texture and mineralogy, there were no valid correlations between SOC and clay, clay+silt or Fe/Al oxide concentrations. Similarly, SOC stocks did not differ significantly when computed for 0–20, 0–40 and 0–100cm layers, and in all soils most SOC was associated with the clay fraction. We propose that such absence of effects of soil parent material, texture and oxide contents on SOC retention can be due to the overriding effect of altitudes of 900–1100m a.s.l., which resulted in higher SOC stocks because of lower mean annual temperatures. These trends are in contrast to those reported for tropical lowlands where the textural and mineralogical controls of SOC retention were first described. Therefore, soils on tropical highlands (>900m) are likely to present similarly high SOC stocks, whereas soil parent material, by means of soil texture, mineralogy and oxide contents would affect SOC retention only at lower altitudes.

Al-/Fe-(hydr)oxides–organic carbon associations in Oxisols — From ecosystems to submicron scales

Al-/Fe(hydr)oxides accumulation upon weathering favors soil organic carbon (SOC) protection into mineral-organic associations (MOAs). Paradoxically, tropical ecosystems on highly weathered soils are characterized by high turnover rates of SOC. Our objective was to propose an explanation for such apparent contradiction by inferring the chemical composition of MOAs in Oxisols. To this end, we compiled a large data set from 43 published articles providing chemical and physical properties of 179 Oxisols/Ferralsols and their SOC content in the A horizon. Thermal analysis (TA) coupled to evolved gas detection (EGD) was used to assess mineral dehydroxylation and SOC oxidation in two soils with contrasting SOC content. Scanning transmission electron microscopy (STEM) was used to probe MOAs within the soil fraction <53μm. At large scales, SOC content was strongly correlated to Al extractable by both ammonium oxalate (AO) (r=0.71) and dithionite-citrate-bicarbonate (DCB) (r=0.41). Weaker, but significant correlations occurred for SOC against Fe-AO and Fe-DCB (r=0.38, and r=014, respectively). At micro-scale, SOC also was found associated to Al-/Fe-(hydr)oxides, as inferred from the STEM imaging. TA-EGD indicated that with increasing SOC content, proportionally more organic matter was oxidized following the dehydroxylation of Al-/Fe-(hydr)oxides at temperatures <400°C. Within the first 20 cm of the topsoil of the Oxisols included in our data set, Al-AO explained 62% of the total variation in SOC. However, while SOC content varied from 0.8 up to 145.8gkg−1 soil, Al-AO varied between 0.2 and 15.3gkg−1 soil. From the perspective of mineral control on SOC retention, reactive species of Al-(hydr)oxides should interact with a disproportionally large amount of organic matter. Because mineral protection is seemingly reduced upon increasing C content in MOAs, SOC in Oxisols may be more vulnerable to environmental changes than currently recognized.

Impact of organic amendments on soil carbon sequestration, water use efficiency and yield of irrigated wheat

Description of the subject. Soil organic carbon (SOC) plays critical role in terrestrial carbon (C) cycling and is central to preserving soil quality, food security and environmental protection in agroecosystem. The prevailing soil and climatic conditions of cultivated and irrigated soils in warm semi-arid areas favor the rapid decomposition, mineralization and loss of SOC to the atmosphere which contribute to global warming. One potential strategy to address this C loss is the addition of organic amendments. Objectives. To investigate the effect of four contrasting organic wastes with and without NPK mineral fertilizer on SOC retention, water use efficiency (WUE) and wheat yield in irrigated wheat-maize cropping system. Method. A 2-year field experiment was conducted using four organic wastes included municipal solid waste (MSW), farm yard manure (FYM), sugar industry waste (filter cake) and maize cropping residues. All wastes were applied at 3 t C·ha-1 alone and with a full or half dose of NPK mineral fertilizer. Results. On average, among organic wastes as sole treatment, highest SOC content in the 0-15 cm layer was recorded in filter cake (6.5 t·ha-1) and MSW (5.9 t·ha-1). Addition of NPK fertilizer along with organic wastes, improved the SOC contents with the highest SOC (7.7 t·ha-1) by filter cake + full NPK treatment followed by the MSW + NPK (6.9 t·ha-1). On average, maximum wheat grain WUE (18 kg·ha-1·mm-1) and grain yield (4.8 t·ha-1) were obtained by MSW + full NPK treatment followed by filter cake + NPK. Conclusions. These results indicate that the targeted addition of organic wastes (filter cake or MSW) have the best potential for improving SOC retention, WUE and wheat yield in irrigated maize-wheat cropping system.

Soil organic carbon pools in ploughed and no‐till Alfisols of central Ohio

AbstractNo‐till (NT) farming can restore the soil organic carbon (SOC) pool of agricultural soils, but the SOC pool size and retention rate can vary with soil type and duration of NT. Therefore, the objectives of this study were to determine the effects of NT and soil drainage characteristics on SOC accumulation across a series of NT fields on Alfisols in Ohio, USA. Sites under NT for 9 (NT9), 13 (NT13), 36 (NT36), 48 (NT48) and 49 (NT49) years were selected for the study. Soil was somewhat poorly drained at the NT48 site but moderately well drained at the other sites. The NT48 and NT49 on‐station sites were under continuous corn (Zea mays), while the other sites were farmers' fields in a corn–soybean (Glycine max) rotation. At each location, the SOC pool (0–30 cm) in the NT field was compared to that of an adjacent plough‐till (PT) and woodlot (WL). At the NT36, NT48 and NT49 sites, the retention rate of corn‐derived C was determined using stable C isotope (13C) techniques. In the 0‐ to 10‐cm soil layer, SOC concentration was significantly larger under NT than PT, but a tillage effect was rarely detected below that depth. Across sites, the SOC pool in that layer averaged 36.4, 20 and 40.8 Mg C/ha at the NT, PT and WL sites, respectively. For the 0‐ to 30‐cm layer, the SOC pool for NT (83.4 Mg C/ha) was still 57% greater than under PT. However, there was no consistent trend in the SOC pool with NT duration probably due to the legacy of past management practices and SOC content differences that may have existed among the study sites prior to their conversion to NT. The retention rate of corn‐derived C was 524, 263 and 203 kg C/ha/yr at the NT36, NT48 and NT49 sites. In contrast, the retention rate of corn‐C under PT averaged 25 and 153 kg C/ha/yr at the NT49 (moderately well‐drained) and NT48 (somewhat poorly drained) sites, respectively. The conversion from PT to NT resulted in greater retention of corn‐derived C. Thus, adoption of NT would be beneficial to SOC sequestration in agricultural soils of the region.

Soil carbon sequestration rates under Mediterranean woody crops using recommended management practices: A meta-analysis

Mediterranean woody crops, such as olive and almond farming, and vineyards are usually cultivated in soils low in organic matter, with limited water availability and frequently on medium to steep slopes. Therefore, when conventionally cultivated, soils of these cropping systems are net sources of CO2 (throughout soil erosion and organic carbon mineralization). A promising option to sequester carbon (C) in these cropping systems is the implementation of recommended management practices (RMPs), which include plant cover in the inter-row area, minimum or no tillage and off- and on-farm organic matter amendments. However, the effects of RMPs on soil organic carbon (SOC) stocks in these cropping systems are widely overlooked, despite the critical importance of estimating their contribution on CO2 emissions for policy decisions in the agriculture sector in Mediterranean regions. We therefore conducted a meta-analysis to derive a C response ratio, soil C sequestration rate and soil C sequestration efficiency under RMPs, compared to conventional management of olive and almond orchards, and vineyards (144 data sets from 51 references). RMPs included organic amendments (OA), plant cover (CC) and a combination of the two (CMP). The highest soil C sequestration rate (5.3tCha−1 yr−1) was observed following the application OA in olive orchards (especially after olive mill pomace application), whereas CC management achieved the lowest C sequestration rates (1.1, 0.78 and 2.0tCha−1 yr−1, for olive orchards, vineyards and almond orchards, respectively). Efficiency of soil C sequestration was greater than 100% after OA and CMP managements, indicating that: i) some of the organic C inputs were unaccounted for, and ii) a positive feedback effect of the application of these amendments on SOC retention (e.g. reduction of soil erosion) and on protective mechanisms of the SOC which reduce CO2 emissions. Soil C sequestration rate tended to be highest during the first years after the change of the management and progressively decreased. Studies performed in Mediterranean sub-climates of low annual precipitation had lower values of soil C sequestration rate, likely due to a lower biomass production of the crop and other plant cover. Soil C sequestration rates in olive farming were much higher than that of vineyards, mainly due to the application of higher annual doses of organic amendments. The relatively high sequestration rate combined with the relative large spatial extent of these cropping system areas suggests that the adoption of RMPs is a sustainable and efficient measure to mitigate climate change.

Ecological stoichiometry controls the transformation and retention of plant-derived organic matter to humus in response to nitrogen fertilisation

Carbon (C) sequestration in soils is a means for increasing soil organic carbon (SOC) stocks and is a potential tool for climate change mitigation. One recommended management practice to increase SOC stocks is nitrogen (N) fertilisation, however examples of positive, negative or null SOC effects in response to N addition exist. We evaluated the relative importance of plant molecular structure, soil physical properties and soil ecological stoichiometry in explaining the retention of SOC with and without N addition. We tracked the transformation of 13C pulse-labelled buffel grass (Cenchrus ciliaris L.), wheat (Triticum aestivum L.) and lucerne (Medicago sativa L.) material to the <53 μm silt + clay soil organic C fraction, hereafter named “humus”, over 365-days of incubation in four contrasting agricultural soils, with and without urea-N addition. We hypothesised that: a) humus retention would be soil and litter dependent; b) humus retention would be litter independent once litter C:N ratios were standardised with urea-N addition; and c) humus retention would be improved by urea-N addition. Two and three-way factorial analysis of variance indicated that 13C humus was consistently soil and litter dependent, even when litter C:N ratios were standardised, and that the effect of urea-N addition on 13C humus was also soil and litter dependent. A boosted regression analysis of the effect of 44 plant and soil explanatory variables demonstrated that soil biological and chemical properties had the greatest relative influence on 13C humus. Regression tree analyses demonstrated that the greatest gains in 13C humus occurred in soils of relatively low total organic C, dissolved organic C and microbial biomass C (MBC), or with a combination of relatively high MBC and low C:N ratio. The greatest losses in 13C humus occurred in soils with a combination of relatively high MBC and low total N or increasing C:N ratio. We conclude that soil variables involved in soil ecological stoichiometry exert a greater relative influence on incorporating organic matter as humus compared to plant molecular structure and soil physical properties. Furthermore, we conclude that the effect of N fertilisation on humus retention is dependent upon soil ecological stoichiometry.