SOC) And Nitrogen Research Articles

Temporal and spatial effects of crop diversity on soil carbon and nitrogen storage and vertical distribution

Species-diverse plant communities can promote the accumulation of soil organic carbon (SOC) and nitrogen (SON) in both natural and semi-natural ecosystems. It is not clear however, how the accumulation and depth distribution of soil C and N might be affected in species-diverse croplands. Using a 15-year crop diversity field experiment, we ask how SOC and SON accumulation and vertical distribution (0-to-100 cm soil depth) changes in response to agricultural diversity, expressed as crop rotation (temporal effect) and intercropping (spatial effect) of staple crop species including wheat and faba bean (C3) and maize (C4). We found that rotation and intercropping across crop combinations altered the depths at which C and N were stored, over the 0–100 cm soil profile, but not the total C and N stored. There was greater SOC storage over the 0–100 cm soil profile in faba bean/maize intercropping than maize-faba bean rotation. Total SOC between 0 and 40 cm soil depth in intercropping increased by 125–164 kg C ha-1 yr-1 compared to rotation systems across crop combinations. However, rotations increased SOC at 60–80 cm in depth by 104 kg ha-1 yr-1 compared to intercropping. Also, SON stocks in rotation systems, at 60–80 cm, increased by 18 kg ha-1 yr-1 compared to intercropping systems. The accumulation and vertical distribution of SOC3 derived from roots of wheat and faba bean contributed to increase total SOC stocks and SOC vertical distribution. SOC4 derived from roots of maize did not have the same effect. Crop rotations promoted deeper root-associated SOC3 accumulation whereas intercropping promoted shallower root-associated SOC3 accumulation. Our study demonstrates how the type of crop diversification influences soil C and N sequestration via regulating root distribution, root composition and root decomposition. These findings have practical implications for soil C and N management in croplands.

Increased Soil Bacterial Abundance but Decreased Bacterial Diversity and Shifted Bacterial Community Composition Following Secondary Succession of Old-Field

Plant secondary succession is a very effective approach for the rejuvenation of degraded ecosystems. In order to comprehend alterations and driving mechanisms of soil bacterial communities under secondary succession of old-field and reveal their subsequent impacts on the decomposition and accumulation of soil organic carbon (SOC) and nitrogen (SON), we investigated changes in soil bacterial communities following ~160 years of old-field succession on the Loess Plateau of China through analyses of quantitative polymerase chain reaction (qPCR) and Illumina MiSeq DNA sequencing of 16S rRNA genes. Our results revealed that subsequent to secondary succession of old-field, soil bacterial abundance progressively increased, while bacterial richness and diversity significantly decreased. Principal component analysis and Bray–Curtis similarity index showed that bacterial community composition gradually shifted following old-field succession. Specifically, the relative abundances of Proteobacteria, Rokubacteria, and Verrucomicrobia progressively increased, while Actinobacteria and Firmicutes slightly decreased following old-field succession. The most enriched of Proteobacteria (e.g., Rhizobiales, Xanthobacteraceae, Gammaproteobacteria, Bradyrhizobium, Rhizobiaceae, and Mesorhizobiur) were found in a climax forest, while Chloroflexi and Gemmatimonadetes had the lowest relative abundances. Further, the most enriched members of Actinobacteria, including Geodermatophilaceae, Frankiales, Blastococcus, Micrococcales, Micrococcacea, Propionibacteriales, Nocardioidaceae, Nocardioide, and Streptomycetaceae, were exhibited in the farmland stage. Our results suggested that secondary succession of old-field greatly modified soil bacterial communities via the transformation of soil nutrients levels, altering plant biomass and soil physiochemical properties. Soil bacterial community composition was transformed from oligotrophic groups to copiotrophic Proteobacteria following old-field succession, which may promote SOC and SON accumulation through increasing the utilization of labile organic carbon (C) and nitrogen (N), while decreasing decomposition of recalcitrant organic C and N from the early- to late-successional stages.

Soil water retention capacity surpasses climate humidity in determining soil organic carbon content but not plant production in the steppe zone of Northern China

Soil hydraulic properties determine water transport, distribution and storage in soils, thus affect ecosystem functioning. Soil water retention parameters, such as saturation water content (SAT), water drained upper limit (DUL) and lower limit (DLL), characterize soil water-holding capacity, thus are important for plant growth and carbon and nutrient cycling in grassland ecosystem. However, we are still unclear to what a content these soil water retention parameters may regulate plant production and soil organic matter content in natural ecosystems in semi-arid grassland environment. We investigated plant species richness (SR) and aboveground biomass (AGB), soil organic carbon (SOC) and nitrogen (SON) contents, and soil water retention and other physical parameters in the steppe ecosystems along a climate transect, which spans the desert steppe, typical steppe and meadow steppe zones in Northern China. We analyzed the relative importance of climate factors, soil water retention parameters and other soil physical parameters in regulating plant AGB and SOC and SON contents using partial correlation analysis, and quantified the contribution of each separate and combined climate and soil physical parameters in predicting plant AGB and SOC and SON contents using geographic detectors method. We found that (i) plant SR and AGB, soil SAT and DUL, and SOC and SON are all significantly inter-correlated, and increased with the increase of climate humidity. (ii) Climate, but not soil physical parameters, was the most preponderant factor in predicting plant SR and AGB. (iii) Soil physical parameters were more important than climate parameters in regulating soil organic matter content; soil DUL was the best predictor to SOC content. Our results suggest that soil water retention parameters especially soil DUL, may play a greater role than climate factors in modulating SOC content, though climate is more predominant in regulating plant SR and production. Our results imply that we need to be cautious in estimating SOC content based on climate factors and vegetation biomass or remotely-sensed vegetation indices, and that soil physical properties need also to be incorporated along with vegetation parameters for improving SOC estimation at a regional scale.

Changes in soil organic carbon and nitrogen pool sizes, dynamics, and biochemical stability during ∼160 years natural vegetation restoration on the Loess Plateau, China

Natural vegetation restoration has been reported as an effective strategy for the enhancement of soil organic carbon (SOC) and nitrogen (SON) sequestration in degraded ecosystems. However, changes in SOC and SON pool sizes, dynamics, and biochemical stability to natural vegetation restoration remain inadequately addressed. For this study, we investigated carbon (C) and nitrogen (N) contents and δ13C and δ15N values of SOC and SON pools, their labile C and N (LSOC and LSON, respectively), and recalcitrant C and N (RSOC and RSON, respectively) along 0–60 cm soil depths spanning ∼160 years of natural vegetation restoration on the Loess Plateau, China. Our results revealed that natural vegetation restoration greatly enhanced SOC, SON, LSOC, LSON, RSOC, total N, water-soluble organic C, and mineralizable organic C in the topsoil (0–20 cm), while it had little influence on the deeper soil layers (20–60 cm). The concentrations and stocks of SOC and SON in the topsoil increased significantly during the later restoration stages. The recalcitrant index for C at the 0–40 cm soil depths was highest in climax Quercus liaotungensis forest, while the recalcitrant index for N was unchanged at 0–20 and 40–60 cm soil depths between vegetation restoration stages. The δ13C values of SOC, LSOC, and RSOC, and δ15N values of SON and LSON were more enriched in the deeper soil layers relative to the topsoil, for the majority of restoration stages. The δ15N values of SON, LSON, and RSON in the topsoil were more enriched during the early restoration stages compared to the later restoration stages. Our results suggested that long-term natural vegetation restoration enhanced SOC and SON sequestration, increased biochemical stability of SOC, altered the dynamics of SOC and SON in the topsoil of degraded ecosystems through the increased inputs of plant residuals, and reduced the decomposition soil organic matter.

Rhizosphere priming regulates soil organic carbon and nitrogen mineralization: The significance of abiotic mechanisms

The effect of living roots on the co-mineralization of soil organic carbon (SOC) and nitrogen (SON) and driving mechanisms of the rhizosphere priming effect (RPE) remains unclear. Moreover, it is still poorly understood whether the abiotic mechanisms, whereby roots accelerate soil organic matter (SOM) loss by destabilizing organo-mineral associations, are involved. Biotic and abiotic processes involved in the RPE and gross N mineralization (GNM) were investigated using three paddy soils (C3) under maize (C4 plant) cultivation. The soils had high and low total N (1.79 and 3.3 g kg−1 soil) as well as iron- (Fe-) (hydr-) oxide (1.1 and 2.2 g kg−1 soil) contents, which gave the following combinations: high-Fe/low-N, low-Fe/low-N, and low-Fe/high-N. The RPEs and GNM were measured using a 13C-natural abundance approach and 15N-pool dilution technique, respectively, on day 86 of maize cultivation. Living roots enhanced native SOC mineralization by 70.4–204% and GNM by 118–382%. As expected, biotic mechanisms contributed to RPEs (‘microbial activation’ and ‘microbial N-mining’) that was supported by the increase of soil microbial biomass C and extracellular enzyme activities in presence of plant, and the lower C/N ratio of primed SOM than the original SOM in unplanted soils. Higher RPEs and relative primed N mineralization via stronger ‘microbial N-mining’ were found in low-Fe/low-N vs low-Fe/high-N soils. In contrast to expectations, the RPEs and relative primed N mineralization were greater in high-Fe/low-N versus low-Fe oxide soils. The strongest decrease in SOM-derived Fe-bound C and increase in root-derived Fe-bound C were observed in the high-Fe soil, because root exudates liberated more C from Fe-bound SOM and co-precipitated with Fe oxides. This shows that the abiotic process was involved in RPEs whereby root exudates promoted soil C loss by releasing it from Fe-organic complexes. Thus, this study demonstrated that coupled biotic-abiotic processes could regulate RPEs.

Similar specific mineralization rates of organic carbon and nitrogen in incubated soils under contrasted arable cropping systems

No tillage is often thought to mitigate greenhouse gas emissions from agricultural land by increasing soil carbon storage, because of a reduced mineralization of soil organic carbon (SOC) and nitrogen (SON). Regrettably, most available references on this topic come from laboratory incubations of disrupted soil from superficial soil layer. Here, we compare SOC and SON mineralization rates in the long-term experiment of La Cage (France) under conventional (CON), low input (LI), conservation agriculture (CA) or organic (ORG) management. Disturbed soil samples from the 0−27 cm soil layer of all treatments were laboratory incubated for four months, while undisturbed CON and CA soil cores were incubated to account for tillage effects. Physical disturbance decreased SOC and SON mineralization. Model fitting showed that the size of the C labile pool and the C and N mineralization rates of the slow pool were 1.5–2.3-fold greater in undisturbed soil cores than in disturbed ones, which may be due to a higher abundance of labile SOC (e.g. plant residues) in undisturbed soil cores. All cropping systems exhibited similar specific rate of mineralization, expressed per unit of SOC, SON or microbial biomass C, both for disturbed and undisturbed soils. Similar mineralization in CA and CON undisturbed soil cores may result from the balance between higher amount of labile OM and less favourable soil structure for decomposition in CA. Similar mineralization rates in disturbed soil cores suggest that OM decomposability and environmental conditions for decomposers were similar between cropping systems. Overall, these results confirmed the hypothesis previously made in silico to explain the differences in SOC storage in this experiment (Autret et al., 2016). Our results together with the increased SOC stocks observed in CA and ORG treatments suggest that increased biomass returns to soil or changes in microbial physiology may be the main drivers of SOC storage.

Overseeding legumes in natural grasslands: Impacts on root biomass and soil organic matter of commercial farms

Overseeding legumes in natural grasslands coupled with phosphorous fertilization are management practices oriented to increase forage production and quality, and to restore nutrient losses generated by livestock. Several studies show increases in forage due to this practice, but less is known about impacts on soil fertility and carbon sequestration. The objective of this study was to evaluate under real farm conditions changes in root C and N stocks and soil organic carbon (SOC) and nitrogen (SON) stocks in two different soil pools, the particulate organic matter (POM) and the mineral associated organic matter (MAOM), after the introduction in natural grasslands of a legume species, Lotus subbiflorus cv. “El Rincón”, accompanied with phosphorous fertilization. We also evaluated changes in the natural abundance of 15N and 13C in soils and roots to understand changes in N fixation and species composition. We selected 12 adjacent paddocks of natural grasslands (NG) and natural grasslands overseeded with legumes and fertilized with phosphorous (NGLP) located in commercial farms in Uruguay. We found that overseeding legumes increased root C and N stocks and SOC and SON stocks in some farms but decreased them in others. On average, no significant differences arose between NGLP and NG paddocks in total stocks of 0–30 cm depth. However, higher C stocks were observed in POM of NGLP paddocks in 0–5 cm layer and lower contents in 5–10 cm layer indicating a change in the vertical distribution of C in POM. Changes in δ15N suggest that atmospheric N is being fixed by legumes in NGLP paddocks, but not translated into more N or C stocks in the MAOM fraction, probably due to high N losses promoted by cattle grazing. Our work suggests that carbon sequestration can be achieved after legumes introduction in grazed natural grasslands but will depend on grazing management practices.

Interaction effects of the main drivers of global climate change on spatiotemporal dynamics of high altitude ecosystem behaviors: process-based modeling.

Soil organic carbon and nitrogen (SOC-N) dynamics are indicative of the human-induced disturbances of the terrestrial ecosystems the quantification of which provides insights into interactions among drivers, pressures, states, impacts, and responses in a changing environment. In this study, a process-based model was developed to simulate the eight monthly outputs of net primary productivity (NPP), SOC-N pools, soil C:N ratio, soil respiration, total N emission, and sediment C-N transport effluxes for cropland, grassland, and forest on a hectare basis. The interaction effect of the climate change drivers of aridity, CO2 fertilization, land-use and land-cover change, and best management practices was simulated on high altitude ecosystems from 2018 to 2070. The best management practices were developed into a spatiotemporally composite index based on SOC-N stock saturation, 4/1000 initiative, and RUCLE-C factor. Our model predictions differed from the remotely sensed data in the range of - 64% (underestimation) for the cropland NPP to 142% (overestimation) for the grassland SOC pool as well as from the global mean values in the range of - 97% for the sediment C and N effluxes to 60% for the total N emission from the grassland. The interaction exerted the greatest negative impact on the monthly sediment N efflux, total N emission, and soil respiration from forest by - 90.5, - 82.7, and - 80.3% and the greatest positive impact on the monthly sediment C effluxes from cropland, grassland, and forest by 139.3, 137.1, and 133.3%, respectively, relative to the currently prevailing conditions.

Soil quality assessment based on soil organic matter pools under long‐term tillage systems and following tillage conversion in a semi‐humid region

AbstractA field study was conducted to assess the long‐term effects of no‐tillage (NT) and conventional tillage (CT), and the short‐term effects following tillage conversion from CT to NT (NTn) and from NT to CT (CTn) on soil quality (SQ) indicators in a semi‐humid climate. First, plots of a long‐term tillage experiment on a Luvic Phaeozem initiated in 1986 were split into two subplots in 2012, yielding four treatments: NT, CT, NTn and CTn. In 2015, composite soil samples were collected from each treatment and from a natural site (Ref) at depths 0–5, 5–10, 10–20 and 0–20 cm. Several indicators were determined: soil organic carbon (SOC) and nitrogen (SON); particulate organic C (POM‐C) and N (POM‐N); potential N mineralization (PMN) and soil respiration (Rs). Moreover, bulk density was determined in long‐term tillage systems. Different ratios between indicators were calculated, with emphasis on its function in the agroecosystem, that is functional indicators. Significant differences in SOC, SON and PMN were found between CT and NT at most depths. In contrast, 3 years after tillage conversion, only a part of the SQ indicators studied were modified mainly at the 0–10 cm depth. The functional indicators showed differences between tillage systems in the long‐term and after short‐term tillage conversion depending on the depth; however, the PMN/SON ratio demonstrated differences at all depths. Under these conditions, this ratio‐related to easily mineralizable N fraction proved to be a promising indicator for assessing SQ under contrasting tillage systems regardless of the sampling depth.

Grain legume-based rotations managed under conventional tillage need cover crops to mitigate soil organic matter losses

Inserting legumes in low-input innovative cropping systems can represent a good strategy to reduce current N fertilizer dependency while enhancing ecosystem services. However, although the impact of the use of legumes as cover crops has been broadly studied, very little is known about the effects of grain legume-based rotations on soil organic carbon (SOC) and nitrogen (SON). A cropping system experiment with three 3-year rotations with different levels of inclusion of grain legumes: GL0, GL1 and GL2 (none, one, and two grain legumes, respectively), with (CC) or without (BF, bare fallow) cover crops was established in SW France (Auzeville) under temperate climate. Durum wheat was present in all the rotations to act as an indicator of their performance. Soil organic C and SON were quantified before the beginning of the experiment and after 3 and 6 years (i.e., after one and two complete 3-yr rotations). Aboveground C and N inputs to the soil, and C and N harvest indexes and grain yield of the cash crops were also measured. Inserting grain legumes in the rotations significantly affected the amount of C and N inputs and consequently SOC and SON. After two cycles of the 3-yr rotation, the GL1 and GL2 treatments showed a greater decrease in SOC and SON when compared to GL0. However, the inclusion of cover crops in the rotations led to mitigate this loss. Durum wheat produced significantly greater grain yields in GL1 when compared to GL0, while GL2 presented intermediate values. In turn, the incorporation of cover crops did not reduce C and N harvest indexes or the grain yield of the different cash crops. We concluded that, in such conventionally-tilled grain legume-based rotations, the use of cover crops was efficient to mitigate SOC and SON losses and then increase N use efficiency at the cropping system level without reducing productivity.

Land degradation impact on soil organic carbon and nitrogen stocks of sub-tropical humid grasslands in South Africa

Land degradation is recognized as a main environmental problem that adversely depletes soil organic carbon (SOC) and nitrogen (SON) stocks, which in turn directly affects soils, their fertility, productivity and overall quality. While it is expanding worldwide at rapid pace, quantitative information on the impact of land degradation on the depletion of SOC and SON stocks remains largely unavailable, limiting the ability to predict the impacts of land management on the C losses to the atmosphere and associated global warming. The main objective of this study was to evaluate the consequences of a decrease in grass aerial cover on SOC and SON stocks. A degraded grassland showing an aerial cover gradient from 100% (Cov100, corresponding to a non-degraded grassland) to 50–75% (Cov75), 25–50% (Cov50) and 0–5% (Cov5, corresponding to a heavily degraded grassland), was selected in South Africa. Soil samples were collected in the 0.05m soil layer at 48 locations along the aerial cover gradient and were subsequently separated into the clay+silt (2–20μm) and sand (20–2000μm) fractions, prior to total C and N analysis (n=288). The decline in grass aerial cover from 100% to 0–5% had a significant (P<0.05) impact on SOC and SON stocks, with losses by as much as 1.25kgm−2 for SOC and 0.074kgm−2 for SON, which corresponded to depletion rates of 89 and 76%, respectively. Furthermore, both the C:N ratio and the proportion of SOC and SON in the silt+clay fraction declined with grass aerial cover, which was indicative of a preferential loss of not easily decomposable organic matter. The staggering decline in SOC and SON stocks raises concerns about the ability of these acidic sandy loam soils to sustain their main ecosystem functions. The associated decrease in chemical elements (e.g., Ca by a maximum of 67%; Mn, 77%; Cu, 66%; and Zn, 82%) was finally used to discuss the mechanisms at stake in land degradation and the associated stock depletion of SOC and SON stocks, a prerequisite to land rehabilitation and stock replenishment.

Patterns of soil organic carbon and nitrogen in relation to soil movement under different land uses in mountain fields (South Central Pyrenees)

Abstract Cultivation on mountain landscapes has been identified as a main factor triggering soil erosion. Patterns of erosion, transport and deposition of soil particles in agricultural landscapes appears to be closely linked to that of soil nutrients. In this work the redistribution of soil organic carbon and nitrogen and of soil particles is analysed in different geomorphic parts of mountain fields. A southern orientated hillslope was selected as representative of main land uses in mountain farmland of the Central Spanish Pyrenees. In the region, as much as 74% of its surface was abandoned in the last decades and as a result patterns of soil and nutrient losses in the fields were affected by both land abandonment and tillage. A set of cultivated and abandoned fields with different ages of land abandonment, slope gradients and lengths were selected to conduct this study. In each of the fields, total soil depth sampling was done in different parts of the slope to assess the pattern distribution of soil organic carbon (SOC) and nitrogen (SON). Other general soil properties analysed: pH, EC, carbonate content, grain size distribution and additional information derived from fallout caesium 137 provided supplementary information for better understanding the patterns of soil and nutrient redistribution. In the cultivated fields SOC and SON contents were higher and comparable to contents in the older abandoned fields, because the recovery of the natural vegetation after a long-term period of abandonment equalized the nutrient conditions in the cultivated fields that had regular additions of manure. In general SOC and SON percentages increased from the upper slope to the bottom slope of the fields with percentage increases ranging from 4 to 54% and from 1.5% to as much as 77%, respectively. Similarly, significant increases of SOC and SON inventories (45 and 49%, respectively) were registered at the bottom slopes of longer fields by comparison with lower increases (33 and 30%, respectively) in shorter and steeper fields. Soil deposition at the bottom slope as indicated by the 137 Cs residuals was paralleled with increases in SOC and SON contents. Under the land use practices in the studied fields the bottom slope positions accumulate soil particles and act as sinks of soil carbon and nitrogen in these mountain agricultural landscapes.

Long-term soil organic carbon and nitrogen dynamics in forage-based crop rotations in Northern Sweden (63–64°N)

For carbon sequestration estimates it is necessary to evaluate effects of management practices on soil organic carbon (SOC) and nitrogen (SON) dynamics in a wide range of production systems and climatic zones. At higher latitudes with cold temperate climate, crop rotations dominated by forage are common and often highly productive—and the climate as well as the forage cropping systems favour large stocks of SOC and SON. The objective of this study was to estimate SOC and SON stock dynamics in the arable layer (0–25 cm) for different 6-year forage-based rotations using sampling data from three long-term field experiments in Northern Sweden. At the site with the lowest initial amount of SOC (8.2 kg C m −2), SOC stocks increased by 12 g C m −2 yr −1 over a 50-year period for the continuous forage rotation (‘A’), which received ca. 10 Mg ha −1 of cattle manure per year (wet mass). At the same site, SOC stocks were more or less at steady state in rotation ‘B’ with 4 years of forage and 2 years of annuals, receiving the same amount of manure. For rotation ‘C’ with 3 years of forage and receiving ca. 6.5 Mg ha −1 of manure, the SOC stocks decreased by 18 g C m −2 yr −1, while the SOC stocks for rotation ‘D’ with only annuals and no manure application decreased by 24 g C m −2 yr −1. At the other two sites, with higher initial SOC stocks (12.1 and 12.8 kg C m −2), the SOC stocks in all treatments decreased during a 30-year period, at a rate ranging from 11 to 95 g C m −2 yr −1. Similar trends were found for the change in SON stocks, although they were more variable. The topsoil SOC stocks were high compared to southern Sweden and regions of similar climate in northeast Canada, in particular for rotation A. These results indicate that the estimates of SOC and SON storage rate changes for a particular management system van vary widely within a small region of a given climatic zone.

Quantifying Straw Removal through Baling and Measuring the Long‐Term Impact on Soil Quality and Wheat Production

Crop residues are considered the feedstock of choice for the production of ethanol, but removing crop residues may negatively impact soil productivity. The objectives were to quantify the proportion of total aboveground crop residues removed through baling and to evaluate the effects of 50 yr of straw removal with baling on soil quality and wheat (Triticum aestivum L.) production. The first study evaluated three harvesting systems and their impact on straw removal with baling. The second study measured straw removal after 50 yr on soil quality and wheat production using a fallow‐spring wheat‐spring wheat rotation (F‐W‐W) with three different treatments imposed. One treatment was not fertilized with straw retained, and the other two were fertilized with N and P but one treatment retained the straw while the other had the straw baled every year during the cropping years. The proportion of total aboveground residues other than grain removed with baling ranged from 22 to 35% or 26 to 40% depending on the method of calculation based on the first study. Measurements of soil organic carbon (SOC) and nitrogen (SON) showed no differences after 50 yr of straw removal, and spring wheat grain yields and grain protein concentration were also not affected based on the second study. The potential therefore exists to use crop residues for ethanol production or other industrial purposes without adversely affecting the long‐term productivity of medium‐ to heavy‐textured soils providing that &lt;40% of the total aboveground residues other than grain are removed and the frequency of removal is no more than 2 yr out of three.

Influence of land use (savanna, pasture, Eucalyptus plantations) on soil carbon and nitrogen stocks in Brazil

SummaryIn Brazil, most Eucalyptus stands have been planted on Cerrado (shrubby savanna) or on Cerrado converted into pasture. Case studies are needed to assess the effect of such land use changes on soil fertility and C sequestration. In this study, the influence of Cerrado land development (pasture and Eucalyptus plantations) on soil organic carbon (SOC) and nitrogen (SON) stocks were quantified in southern Brazil. Two contrasted silvicultural practices were also compared: 60 years of short‐rotation silviculture (EUCSR) versus 60 years of continuous growth (EUCHF). C and N soil concentrations and bulk densities were measured and modelled for each vegetation type, and SOC and SON stocks were calculated down to a depth of 1 m by a continuous function.Changes in SOC and SON stocks mainly occurred in the forest floor (no litter in pasture and up to 0.87 kg C m−2 and 0.01 kg N m−2 in EUCSR) and upper soil horizons. C and N stocks and their confidence intervals were greatly influenced by the methodology used to compute these layers. C/N ratio and 13C analysis showed that down to a depth of 30 cm, the Cerrado organic matter was replaced by organic matter from newly introduced vegetation by as much as 75–100% for pasture and about 50% for EUCHF, poorer in N for Eucalyptus stands (C/N larger than 18 for Eucalyptus stands). Under pasture, 0–30 cm SON stocks (0.25 kg N m−2) were between 10 and 20% greater than those of the Cerrado (0.21 kg N m−2), partly due to soil compaction (limit bulk density at soil surface from 1.23 for the Cerrado to 1.34 for pasture). Land development on the Cerrado increased SOC stocks in the 0–30 cm layer by between 15 and 25% (from 2.99 (Cerrado) to 3.86 (EUCSR) kg C m−2). When including litter layers, total 0–30 cm carbon stocks increased by 35% for EUCHF (4.50 kg C m−2) and 53% for EUCSR (5.08 kg C m−2), compared with the Cerrado (3.28 kg C m−2), independently of soil compaction.

Soil organic C and N fractions under continuous cropping with contrasting tillage systems on mollisols of the southeastern Pampas

Cropping alters soil quality, and tillage intensity and residue input affects soil organic carbon (SOC) and nitrogen (SON). The aim of this work was to evaluate the changes in SOC and SON, of their particulate fractions (POC and PON), mineralizable N (anaerobic incubations, AN), and corn yield, in response to tillage systems and N fertilization under continuous cropping. Such variables were evaluated in 2001 and 2004 in a long-term experiment started in 1997 on a non-degraded complex of Typic Argiudoll and Petrocalcic Paleudoll soils at Balcarce, Argentina (37°45′S, 58°18′W). Tillage systems were conventional (CT) and no-tillage (NT) combined with continuous N fertilization and no N fertilization. Treatment factors did not differentially affect bulk density (BD) although a trend towards a higher BD could be seen under NT and in 2004. Neither tillage system nor N fertilization affected differentially SOC, SON, POC, nor PON contents with the exception of the 0–5 cm layer where higher contents and a trend to higher contents were observed under NT and with N, respectively. However, despite little changes in SOC and SON contents respect to the beginning of the experiment occurred along it, significant decreases were observed between 1997 and 2001 and great increases arose between 2001 and 2004. These changes were related to the level of annual residue input in each period associated to weather conditions. No changes were observed in AN, which means that soil capacity to supply N to crops was not affected. Corn yield was highly affected by water availability in each of the studied growing seasons. However, when no N was applied, grain yield was greater under CT. Although potentially mineralizable N was not affected by treatment factors, the capacity of providing N to corn was expressed only when mineralization was promoted by tillage. Hence, rationally tilling this non-degraded mollisol with low risk of erosion would allow to take advantage of its potential of N supply and to a safe N fertilization reducing environmental risks due to excess of fertilizer. As long as it were assured a high average annual residue input, no significant changes in soil organic fractions would be expected during a relatively long period of use.

Quantifying Carbon Budgets Of Conifer Mediterranean Forest Ecosystems, Turkey

Aboveground biomass, aboveground litterfall, and leaf litter decomposition of five indigenous tree stands (pure stands of Pinus brutia, Pinus nigra, Cedrus libani, Juniperus excelsa, and a mixed stand of Abies cilicica, P. nigra, and C. libani) were measured in an eastern Mediterranean evergreen needleleaf forest of Turkey. Measurements were converted to regional scale estimates of carbon (C) stocks and fluxes of forest ecosystems, based on general non-site-specific allometric relationships. Mean C stock of the conifer forests was estimated as 97.8 +/- 79 Mg C ha(-1) consisting of 83.0 +/- 67 Mg C ha(-1) in the aboveground and 14.8 +/- 12 Mg C ha(-1) in the belowground biomass. The forest stands had mean soil organic carbon (SOC) and nitrogen (SON) stocks of 172.0 +/- 25.7 Mg C ha(-1) and 9.2 +/- 1.2 Mg N ha(-1), respectively. Mean total monthly litterfall was 376.2 +/- 191.3 kg C ha(-1), ranging from 641 +/- 385 kg C ha(-1) for Pinus brutia to 286 +/- 82 kg C ha(-1) for Cedrus libani. Decomposition rate constants (k) for pine needles were 0.0016 for Cedrus libani, 0.0009 for Pinus nigra, 0.0006 for the mixed stand, and 0.0005 day(-1) for Pinus brutia and Juniperus excelsa. Estimation of components of the C budgets revealed that the forest ecosystems were net C sinks, with a mean sequestration rate of 2.0 +/- 1.1 Mg C ha(-1) yr(-1) ranging from 3.2 +/- 2 Mg C ha(-1) for Pinus brutia to 1.6 +/- 0.6 Mg C ha(-1) for Cedrus libani. Mean net ecosystem productivity (NEP) resulted in sequestration of 98.4 +/- 54.1 Gg CO2 yr(-1) from the atmosphere when extrapolated for the entire study area of 134.2 km2 (Gg = 10(9) g). The quantitative C data from the study revealed the significance of the conifer Mediterranean forests as C sinks.

Soil carbon and nitrogen changes as affected by tillage system and crop biomass in a corn–soybean rotation

A wide range of tillage systems have been used by producers in the Corn-Belt in the United States during the past decade due to their economic and environmental benefits. However, changes in soil organic carbon (SOC) and nitrogen (SON) and crop responses to these tillage systems are not well documented in a corn–soybean rotation. Two experiments were conducted to evaluate the effects of different tillage systems on SOC and SON, residue C and N inputs, and corn and soybean yields across Iowa. The first experiment consisted of no-tillage (NT) and chisel plow (CP) treatments, established in 1994 in Clarion–Nicollet–Webster (CNW), Galva–Primghar–Sac (GPS), Kenyon–Floyd–Clyde (KFC), Marshall (M), and Otley–Mahaska–Taintor (OMT) soil associations. The second experiment consisted of NT, strip-tillage (ST), CP, deep rip (DR), and moldboard plow (MP) treatments, established in 1998 in the CNW soil association. Both corn and soybean yields of NT were statistically comparable to those of CP treatment for each soil association in a corn–soybean rotation during the 7 years of tillage practices. The NT, ST, CP, and DR treatments produced similar corn and soybean yields as MP treatment in a corn–soybean rotation during the 3 years of tillage implementation of the second experiment. Significant increases in SOC of 17.3, 19.5, 6.1, and 19.3% with NT over CP treatment were observed at the top 15-cm soil depth in CNW, KFC, M, and OMT soil associations, respectively, except for the GPS soil association in a corn–soybean rotation at the end of 7 years. The NT and ST resulted in significant increases in SOC of 14.7 and 11.4%, respectively, compared with MP treatment after 3 years. Changes in SON due to tillage were similar to those observed with SOC in both experiments. The increases in SOC and SON in NT treatment were not attributed to the vertical stratification of organic C and N in the soil profile or annual C and N inputs from crop residue, but most likely due to the decrease in soil organic matter mineralization in wet and cold soil conditions. It was concluded that NT and ST are superior to CP and MP in increasing SOC and SON in the top 15 cm in the short-term. The adoption of NT or CP can be an effective strategy in increasing SOC and SON in the Corn-Belt soils without significant adverse impact on corn and soybean yields in a corn–soybean rotation.

Soil Carbon and Nitrogen Storage in Aggregates from Different Tillage and Crop Regimes

No-tillage (NT) has the potential to enhance C and N sequestration in agricultural soils of the southern USA, but results may vary with crop species. The objectives of this study were to investigate the impacts of NT, conventional tillage (CT), and crop species on soil organic carbon (SOC) and nitrogen (SON) sequestration and distribution within aggregate-size fractions in a central Texas soil after 20 yr of management. No-tillage increased SOC over CT at the 0- to 5-cm depth by 97, 47, and 72%, and SON by 117, 56, and 44% for continuous grain sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.J, respectively. Crop species had significant impacts on SOC and SON sequestration. On average, the wheat monoculture had greater SOC (9.23 Mg C ha -1 ) at the 0- to 5-cm depth than sorghum (6.75 Mg C ha -1 ) and soybean (7.05 Mg C ha -1 ). No-tillage increased the proportion of >2-mm and 250-μm to 2-mm macroaggregate fractions in soil compared with CT. At the 0- to 5-cm depth, NT increased SOC compared with CT by 158% in macroaggregate fractions, but only 40% in 2-mm, 250-μm to 2-mm, 53- to 250-μm, and <53-μm fractions, respectively. Long-term impacts of NT included a greater proportion of macroaggregates and increased C and N sequestration, but impacts were dependent on crop species and varied with soil depth.

Tillage impacts on microbial biomass and soil carbon and nitrogen dynamics of corn and cotton rotations

Long-term no tillage (NT) may enhance soil C sequestration and alter soil C and N dynamics. The objectives of this study were to investigate the impacts of tillage on soil C and N sequestration and microbial C and N dynamics of corn ( Zea mays L.) and cotton ( Gossypium hirsutum L.) cropping sequences after 20 years of management. Tillage regimes included conventional tillage (CT), moldboard plow (MP), minimum tillage (MT), and NT. No tillage increased soil organic carbon (SOC) and nitrogen (SON) concentrations in surface soil (0–2.5 cm) for cotton but not for corn. Few tillage effects on SOC and SON were observed in subsurface soils. For corn, SOC and SON were 11 and 21% higher under NT than other tillage regimes at 0–2.5 cm, but were 22 and 12% lower under NT from 2.5 to 20 cm. Averaged between depths, SOC and SON for cotton were 8 and 7% greater under NT than CT, while NT and MT had 24 and 43% greater SOC and SON than MP. Soil organic C and SON were significantly greater for corn than cotton, but this did not result in greater microbial biomass and mineralizable C and N than for cotton. Microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were often highest under NT and MT in surface soils, but few tillage impacts were observed at 2.5–20 cm. Mineralizable C and N were highest under NT and MT in surface soils for corn and cotton, and in subsurface soils for cotton. Even though SOC and SON were greater for corn than cotton, cotton exhibited greater soil mineralizable C and N under NT and MT than corn, especially in subsurface soils. These results indicate a greater potential supply of N for the cotton than corn crop during the growing season. Increased SOM content in surface soils under reduced tillage may increase N mineralization and the nutrient supply to crops, but the potential of these soils for C and N sequestration appeared limited.