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Soil Carbon Sequestration
Conservation Agriculture and Soil Carbon Sequestration:... Featured
Global food security, global environmental preservation as well as farmer level increased livelihood should be the main goals of a sustainable farming system in today’s world plagued by degraded soils as a result of unsustainable crop management practices. The multitude of rural farmers as well as the three billion urban consumers must rely on sustainable food production systems for their livelihoods. Current agricultural management systems are threatened by increasing competition for ever-scarce water resources combined with continued use by most farmers of highly inefficient irrigation systems. Despite the availability of improved varieties with increased yield potential, the potential increase in production is not attained because of poor crop system management (Reynolds and Tuberosa, 2008). Persistent use of conventional farming practices based on extensive tillage have magnified soil erosion losses and the soil resource base has been steadily degraded, especially when tillage is combined with in si ...
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The Relationship between Carbon Input, Aggregation, and... Featured
One of our current challenges is to quantify the mechanisms, capacity, and longevity of C stabilization in agricultural lands. The objectives of this study were to evaluate the long-term (10 yr) role of C input in soil organic carbon (SOC) sequestration and to identify underlying mechanisms of C stabilization in soils. Carbon input and SOC sequestration, as governed by crop management strategies, were assessed across 10 Mediterranean cropping systems. Empirically derived relationships between yield and aboveground plus belowground crop biomass as well as estimates of C contributions from crop residues and manure amendments were used to quantify cumulative C inputs into each cropping system. Soil samples were separated into four aggregate size classes (>2000, 250–2000, 53–250, and <53 µm) and into three soil organic matter (SOM) fractions within the large (>2000 µm) and small (250–2000 µm) macroaggregates. Aggregate stability increased linearly with both C input (r2 = 0.75, p = 0.001) and SOC (r2 ...
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Carbon Sequestration in Microaggregates of No-Tillage S... Featured
Identification of diagnostic soil organic matter (SOM) fractions and the mechanisms controlling their formation and turnover is critical for better understanding of C dynamics in soils. Enhanced microaggregate formation and stabilization of C due to reduced macroaggregate turnover has been proposed as a mechanism promoting C sequestration in no-tillage (NT) compared with conventional tillage (CT) systems in temperate soils dominated by 2:1 clay mineralogy. We evaluated the contribution of macroaggregate-protected microaggregates to total soil organic carbon (SOC) sequestration in NT relative to CT in three soils differing in clay mineralogy: a 2:1 clay-dominated soil (2:1), a soil with mixed clay mineralogy [2:1 and 1:1] and oxides (mixed), and a soil dominated by (1:1) clay minerals and oxides (1:1). Microaggregates (mM) were isolated from macroaggregates from 0- to 5- and 5- to 20-cm soil layers. Particulate organic matter (POM) located within the microaggregates (intra-mM-POM) was separated from POM ou ...
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Carbon Turnover Kinetics with Depth in a French Loamy S... Featured
Soil C dynamics below the plow layer have been little studied, in spite of proven large C stocks and suspected large C stabilization potential. The objective of the present study was to determine C-turnover kinetics throughout the 1-m profile of a cultivated loam soil of the Paris basin, France. The soil 13C signature was determined to depths of 1.05 m in 32 replicated plots having received from 0 to 10 yr of maize after wheat. Above- and below-ground maize-residue biomass inputs were estimated throughout the 10-yr period. After 10 yr, maize-derived soil organic carbon (SOC) constituted about 10, 5, and 2% of the total SOC at 15-, 50-, and 100-cm depths, respectively. About one-third of recently deposited maize-derived SOM present in the 1-m soil profile was retrieved below the Ap horizon. The ratios of maize-derived soil C to the cumulative maize above- and below-ground inputs over the 10-yr period averaged 17% across the soil profile. This ratio was lower in the Ap horizon (i.e., 13%) than in deeper soi ...
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Changes in Soil Organic Matter Fractions under Subtropi... Featured
Conservation management systems increase soil C and N pools. However, their effects on particulate (>53 µm) and mineral-associated (<53 µm) soil organic matter (SOM) fractions are less understood under subtropical climatic conditions. This study evaluated the long-term (12-yr) effects of three no-till cropping systems on C and N pools in particulate and mineral-associated SOM. The study was performed in southern Brazil, on a sandy clay loam Acrisol. Cropping systems that included cover crops increased C and N pools in both particulate and mineral-associated SOM when compared with BS. Mineral-associated SOM had five to nine times more C and 13 to 26 times moreN than particulate organic matter and was responsible for 69 to 80% of total atmospheric CO2 sequestred by soil in O + V/M + C (38 Mg ha-1 ) and M + C (51 Mg ha-1 ). The higher C and N pools were associated with greater recalcitrance of mineral-associated SOM to biological decomposition, resulting from its inter-action with variable charge minerals ...
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Effects of Cover Crops on Soil Aggregate Stability, Tot... Featured
Structural degradation of silt clay loam soils in Delta, British Columbia, has resulted from intensive cultivation of vegetable crops. A field experiment and a laboratory incubation study were conducted to assess the ability of nonleguminous winter cover crops, spring barley (Hordeum vulgare L.), fall rye (Secale cereale L.), and annual ryegrass (Lolium multiflorum Lam.), to affect soil organic C, total and dilute acid extractable polysaccharides, and aggregate stability, expressed as mean weight diameter (MWD). The field experiment included four treatments: three cover crops (spring barley, fall rye, and annual ryegrass) and control (bare soil) arranged in a randomized complete block design. Annual ryegrass and fall rye increased MWD, and all of the cover crops increased soil dilute acid extractable polysaccharides. In the incubation experiment, starch (2.68 g C kg–1 soil) or chopped shoots and coarse roots of fall rye (single- [4.14 g C kg–1 soil] and double-dose [8.28 g C kg–1 soil]) and annual r ...
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Crop and Soil Productivity Response to Corn Residue Rem... Featured
Society is facing three related issues: overreliance on imported fuel, increasing levels of greenhouse gases in the atmosphere, and producing sufficient food for a growing world population. The U.S. Department of Energy and private enterprise are developing technology necessary to use high-cellulose feedstock, such as crop residues, for ethanol production. Corn (Zea mays L.) residue can provide about 1.7 times more C than barley (Hordeum vulgare L.), oat (Avena sativa L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max (L.) Merr.], sunflower (Helianthus annuus L.), and wheat (Triticum aestivum L.) residues based on production levels. Removal of crop residue from the field must be balanced against impacting the environment (soil erosion), maintaining soil organic matter levels, and preserving or enhancing productivity. Our objective is to summarize published works for potential impacts of wide-scale, corn stover collection on corn production capacity in Corn Belt soils. We address the issue of ...
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Dynamics and Turnover of Soil Organic Matter as Affecte... Featured
Greater knowledge of the dynamics of organic matter in different locations in the soil matrix can provide valuable information for implementing tillage practices that may favor C sequestration and improve soil quality. The objective of this study was to investigate the effect of tillage practices on the dynamics and turnover of organic matter located outside (free light fraction [FLF]) and inside (occluded light fraction [OLF]) aggregates, and in intimate association with soil minerals (heavy fraction [HF]). Composite soil samples from 11-yr-old corn (Zea mays L.) plots under no-till (NT) and conventional tillage (CT) practices, and from >60-yr-old tobacco (Nicotiana tabacum L.)–rye (Secale cereale L.) plots under CT were fractionated into these fractions, and changes in the amounts of total soil organic C (SOC), corn-derived (C4) C, and native (C3) C and the turnover of native C as a consequence of tillage were estimated. Adoption of NT increased (P < 0.05) standing SOC and C4–C stocks in whole soil ...
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Edaphic Controls on Soil Organic Carbon Retention in th... Featured
Soil organic carbon (SOC) retention is a function of climate, vegetation, drainage, and management interactions, but also of intrinsic soil properties such as texture, mineralogy, and structure. To assess these edaphic controls, three soils of the Brazilian savanna (Cerrado) under similar climate, vegetation, and slope but of contrasting texture were sampled to 1-m depth and characterized for textural, chemical, and mineralogical properties, and SOC concentration (in bulk samples and clay, silt, and sand fractions). The basic assumption was that SOC particle size determines its retention mechanism: colloidal forms are retained by sorption, while particulate organic matter (>20 µm) can occur outside or inside aggregates. It was hypothesized that SOC retention is controlled simultaneously by soil texture, mineralogy, and depth. The three soils are clayey, loamy, and sandy Haplustox, all kaolinitic with minor contents of Fe and Al oxides, vermiculite, and illite. The SOC concentrations in particle size frac ...
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Managing Soil Carbon Featured
Current farming practices deplete soil carbon, which degrades soil quality, reduces productivity, and results in the need for more fertilization, irrigation, and pesticides. No-till farming with residue mulching would reverse these effects by slowing soil erosion and pollution runoff, benefiting aquatic ecosystems, improving agronomic productivity, and achieving food security. The authors of this Policy Forum urge support for its wider use. Although there may be short-term yield reductions in some soils and climates, this is a win-win opportunity for the vast majority of the 95% of the cropland that does not use these more sustainable practices.
Measuring and Understanding Carbon Storage in Afforeste... Featured
Forested ecosystems have been identified as potential C sinks. However, the accuracy of measurement and understanding of the underlying mechanisms for soil organic C (SOC) storage in forested ecosystems needs to be improved. The objective of this study was to use aggregate and soil organic matter (SOM) fractionation techniques to identify SOC pools that preferentially stabilize SOC in the long term and elucidate SOC sequestration mechanisms in forested soils. At two sites (Wildlife area, Ohio and Kemptville, Ontario) representing two different soils (Hapludalf and Hapludoll), we sampled soils under agriculture, afforestation, and forest and separated them into aggregates. Different size classes of intra-aggregate particulate organic matter (iPOM) fractions were isolated by density flotation, dispersion, and sieving. At both sites, aggregation and whole SOC content were greater in the forested than in the agricultural ecosystems. The greater aggregation in forested ecosystems resulted in greater iPOM C con ...
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Organic Matter Dynamics and Carbon Sequestration Rates ... Featured
Amounts and rates of C sequestration under no-tillage are not known for a major ecological region of south Brazil. These were assessed in a Brazilian Oxisol under a plow and no-tillage chronosequence located in Paraná State. The chronosequence consisted of six treatments: (i) native field (NF); (ii) 1-yr plow conversion of native field to cropland (PNF-1); (iii) no-tillage for 10 yr (NT-10); (iv) no-tillage for 20 yr (NT-20); (v) no-tillage for 22 yr (NT-22); and (vi) conventional tillage for 22 yr (CT-22). Soil samples were collected from five depths. No-tillage, compared with the NF treatment, caused a significant increase in soil organic C (SOC) storage. More than 60% of this increase occurred in the 0- to 10-cm soil layer. There was a decrease in the amount of SOC in the CT-22 compared with the NF soil treatment and 97% of this loss also occurred in the 0- to 10-cm layer. There was a close relationship between the SOC content and the amount of crop residues input (R2 = 0.74, P <= 0.05). There were in ...
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Soil Carbon and Nitrogen Organic Fractions in Degraded ... Featured
The use of no-tillage has notably increased in the Pampas region of Argentina during the last 10 yr. Two tillage experiments with contrasting previous agricultural use, degraded and non-degraded soils, were evaluated in the southeast of Buenos Aires province, Argentina. The objectives were to: (i) quantify the effects of tillage and N fertilization on quantity and vertical distribution of C and N in the soil organic matter (SOM) and particulate organic matter (POM) fractions as well as potentially mineralizable N (PMN), and (ii) evaluate these fractions as indicators of soil quality. Tillage systems were conventional tillage (CT), minimum tillage (MT), and no-tillage (NT) (main plots), and N fertilization rates were 0, 120, and 150 kg ha-1 (subplots). Total organic C (TOC), total N (TN), POM-C, POM-N, and PMN were measured at 0- to 7.5- and 7.5- to 15-cm soil depth. In Exp. I (degraded soil) TOC was greater under NT (27 g kg-1) than under CT (24 g kg-1) in the 0-N treatments. No differences in TOC and TN ...
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Soil Aggregation and Carbon and Nitrogen Storage under ... Featured
Management practices, such as no-tillage (NT) and high-intensity cropping sequences, have the potential to enhance C and N sequestration in agricultural soils. The objectives of this study were to investigate the impacts of conventional-tillage (CT), NT, and multiple cropping sequences on soil organic carbon (SOC) and nitrogen (SON) sequestration and on distribution within aggregate-size fractions in a southcentral Texas soil after 20 yr of treatment imposition. No-tillage management increased soil aggregation compared with CT, with the bulk of SOC and SON storage present in larger aggregate-size fractions (>2 mm, 250 µm to 2 mm) at both soil depths. Multiple cropping systems, such as a grain sorghum [Sorghum bicolor (L.) Moench]/wheat (Triticum aestivum L.)/soybean [Glycine max (L.) Merr] (SWS) rotation and a wheat/soybean (WS) doublecrop had the highest SOC and SON storage, while the continuous monoculture soybean treatment had the lowest storage. Soil organic C and SON storage were significantly great ...
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Soil macroaggregate turnover and microaggregate formati... Featured
Soil disturbance from tillage is a major cause of organic matter depletion and reduction in the number and stability of soil aggregates when native ecosystems are converted to agriculture. No-till (NT) cropping systems usually exhibit increased aggregation and soil organic matter relative to conventional tillage (CT). However, the extent of soil organic matter changes in response to NT management varies between soils and the mechanisms of organic matter stabilization in NT systems are unclear. We evaluated a conceptual model which links the turnover of aggregates to soil organic matter dynamics in NT and CT systems; we argue that the rate of macroaggregate formation and degradation (i.e. aggregate turnover) is reduced under NT compared to CT and leads to a formation of stable microaggregates in which carbon is stabilized and sequestered in the long term. Therefore, the link between macroaggregate turnover, microaggregate formation, and C stabilization within microaggregates partly determines the observed ...
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No-Tillage and Soil-Profile Carbon Sequestration: An On... Featured
No-tillage (NT) farming is superior to intensive tillage for conserving soil and water, yet its potential for sequestering soil organic carbon (SOC) in all environments as well as its impacts on soil profile SOC distribution are not well understood. Thus, we assessed the impacts of long-term NT-based cropping systems on SOC sequestration for the whole soil profile (0–60-cm soil depth) across 11 Major Land Resource Areas (MLRAs: 121, 122, and 125 in Kentucky; 99, 124, 139A in Ohio; and 139B, 139C, 140, 147, and 148 in Pennsylvania) in the eastern United States. Soil was sampled in paired NT and plow tillage (PT) based cropping systems and an adjacent woodlot (WL). No-tillage farming impacts on SOC and N were soil specific. The SOC and N concentrations in NT soils were greater than those in PT soils in 5 out of 11 MLRAs (121, 122, 124, 139A, and 148), but only within the 0- to 10-cm depth. Below 10 cm, NT soils had lower SOC than PT soils in MLRA 124. The total SOC with NT for the whole soil profile (0†...
Organic matter: improving soil fertility and structure Featured
One objective of long-term sustainable agriculture is the conservation of soil organic matter (SOM). Management of SOM in agro-ecosystems should mimic natural ecosystems by maximizing retention and recycling of organic matter and plantnutrients, and should minimize losses of these soil components caused by leaching, runoff and erosion.
Cropping Intensity Enhances Soil Organic Carbon Featured
Soil organic C (SOC) has decreased under cultivated wheat (Triticum aestivum)-fallow (WF) in the central Great Plains. We evaluated the effect of no-till systems of WF, wheat–corn (Zea Mays)-fallow (WCF), wheat–corn–millet (Panicum miliaceum)-fallow, continuous cropping (CC) without monoculture, and perennial grass (G) on SOC and total N (TN) levels after 12 yr at three eastern Colorado locations. Locations have long-term precipitation averages of 420 mm but increase in potential evapotranspiration (PET) going from north to south. Within each PET location, cropping systems were imposed across a topographic sequence of summit, sideslope, and toeslope. Cropping intensity, slope position, and PET gradient (location) independently impacted SOC and TN to a 5-cm soil depth. Continuous cropping had 35 and 17% more SOC and TN, respectively, than the WF system. Cropping intensity still impacted SOC and TN when summed to 10 cm with CC > than WF. Soil organic C and TN increased 20% in the CC system compared wi ...
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Potential Long-Term Benefits of No-Tillage and Organic ... Featured
There have been few comparisons of the performance of no-tillage cropping systems vs. organic farming systems, particularly on erodible, droughty soils where reduced-tillage systems are recommended. In particular, there is skepticism whether organic farming can improve soils as well as conventional no-tillage systems because of the requirement for tillage associated with many organic farming operations. A 9-yr comparison of selected minimum-tillage strategies for grain production of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) was conducted on a sloping, droughty site in Beltsville, MD, from 1994 to 2002. Four systems were compared: (i) a standard mid-Atlantic no-tillage system (NT) with recommended herbicide and N inputs, (ii) a cover crop-based no-tillage system (CC) including hairy vetch (Vicia villosa Roth) before corn, and rye (Secale cereale L.) before soybean, with reduced herbicide and N inputs, (iii) a no-tillage crownvetch (Coronilla varia L.) living mul ...
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AGROSYSTEMS AND CARBON SEQUESTRATION. THE CASE OF DIREC... Featured
Direct sowing mulch-based cropping Systems, mostly with crop residues that protect soil between two successive cultures have been adopted to fight against soil degradation i.e. wind or water erosion. Thereafter, to face situations where the crop residues disappear quickly (tropical humid climate or residues removal) living covers have been proposed. The possibility to master, for a long time in tropical environment, a System where crops and cover plants follow each other and its economic interest have been recognized. Progress are especially achieved in the selection within these Systems of crop varieties and plant cover species. After presenting the design principles of these cropping Systems, results obtained in various tropical areas are shown. Yield levels are close to and even higher than those obtained in classical soil tillage Systems, with less work. The inputs are reduced because of the mineral enrichment of the subsoil and of the herbicidaleffect of the plant covers. The organic matter accumulat ...
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