NT Soils Research Articles

Computed tomography scanning revealed macropore-controlled N2O emissions under long-term tillage and cover cropping practices

Microscale alterations in soil physical characteristics resulting from long-term soil health practices can contribute to changes in soil nitrous oxide (N2O) emissions. In this study, we investigated soil N2O emissions in relation to pore characteristics influencing soil gas diffusivity under long-term tillage and cover cropping practices. Intact soil cores from tillage (conventional tillage, Conv. T versus no tillage, NT) and cover crop (hairy vetch, HV versus no cover crop, NC) treatments were used for N2O measurements and computed tomography (CT) scanning. Using X-ray CT technique with a resolution of 59 μm, pore structure parameters including macroporosity, number of macropores, anisotropy, fractal dimension, tortuosity, and connectivity were determined. The results showed that Conv. T and HV emitted significantly higher N2O than NT and NC, respectively. A similar trend was observed for macroporosity, Conv. T soils had 27.4 % higher CT-derived macroporosity than the NT soils and HV increased macroporosity by 31.1 % over the NC treatment. The number of macropores and fractal dimension were significantly higher whereas degree of anisotropy was significantly lower under HV compared to NC. In the upper 3 cm of soil, HV had a connected porosity, whereas the pores were disconnected and isolated in NC. These CT-derived properties; however, were not impacted by tillage treatments. N2O emissions were positively and significantly correlated to relative soil gas diffusivity, CT-derived macroporosity, number of macropores, and fractal dimension. Our results demonstrated that soil macroporosity and relative gas diffusivity could lead to improved understanding and predictability of N2O emissions under high soil moisture conditions.

Spatio-temporal microbial regulation of aggregate-associated priming effects under contrasting tillage practices

Tillage intensity significantly influences the heterogeneous distribution and dynamic changes of soil microorganisms, consequently shaping spatio-temporal patterns of SOC decomposition. However, little is known about the microbial mechanisms by which tillage intensity regulates the priming effect (PE) dynamics in heterogeneous spatial environments such as aggregates. Herein, a microcosm experiment was established by adding 13C-labeled straw residue to three distinct aggregate-size classes (i.e., mega-, macro-, and micro-aggregates) from two long-term contrasting tillage histories (no-till [NT] and conventional plow tillage [CT]) for 160 days to observe the spatio-temporal variations in PE. Metagenomic sequencing and Fourier transform mid-infrared techniques were used to assess the relative importance of C-degrading functional genes, microbial community succession, and SOC chemical composition in the aggregate-associated PE dynamics during straw decomposition. Spatially, straw addition induced a positive PE for all aggregates, with stronger PE occurring in larger aggregates, especially in CT soil compared to NT soil. Larger aggregates have more unique microbial communities enriched in genes for simple C degradation (e.g., E5.1.3.6, E2.4.1.7, pmm-pgm, and KduD in Nitrosospeera and Burkholderia), contributing to the higher short-term PE; however, CT soils harbored more genes for complex C degradation (e.g., TSTA3, fcl, pmm-pgm, and K06871 in Gammaproteobacteria and Phycicoccus), supporting a stronger long-term PE. Temporally, soil aggregates played a significant role in the early-stage PEs (i.e., < 59 days after residue addition) through co-metabolism and nitrogen (N) mining, as evidenced by the increased microbial biomass C and dissolved organic C (DOC) and reduced inorganic N with increasing aggregate-size class. At a later stage, however, the legacy effect of tillage histories controlled the PEs via microbial stoichiometry decomposition, as suggested by the higher DOC-to-inorganic N and DOC-to-available P stoichiometries in CT than NT. Our study underscores the importance of incorporating both spatial and temporal microbial dynamics for a comprehensive understanding of the mechanisms underlying SOC priming, especially in the context of long-term contrasting tillage practices.

A Parsimonious Approach to Estimate Soil Organic Carbon Applying Unmanned Aerial System (UAS) Multispectral Imagery and the Topographic Position Index in a Heterogeneous Soil Landscape

Remote sensing plays an increasingly key role in the determination of soil organic carbon (SOC) stored in agriculturally managed topsoils at the regional and field scales. Contemporary Unmanned Aerial Systems (UAS) carrying low-cost and lightweight multispectral sensors provide high spatial resolution imagery (&lt;10 cm). These capabilities allow integrate of UAS-derived soil data and maps into digitalized workflows for sustainable agriculture. However, the common situation of scarce soil data at field scale might be an obstacle for accurate digital soil mapping. In our case study we tested a fixed-wing UAS equipped with visible and near infrared (VIS-NIR) sensors to estimate topsoil SOC distribution at two fields under the constraint of limited sampling points, which were selected by pedological knowledge. They represent all releva nt soil types along an erosion-deposition gradient; hence, the full feature space in terms of topsoils’ SOC status. We included the Topographic Position Index (TPI) as a co-variate for SOC prediction. Our study was performed in a soil landscape of hummocky ground moraines, which represent a significant of global arable land. Herein, small scale soil variability is mainly driven by tillage erosion which, in turn, is strongly dependent on topography. Relationships between SOC, TPI and spectral information were tested by Multiple Linear Regression (MLR) using: (i) single field data (local approach) and (ii) data from both fields (pooled approach). The highest prediction performance determined by a leave-one-out-cross-validation (LOOCV) was obtained for the models using the reflectance at 570 nm in conjunction with the TPI as explanatory variables for the local approach (coefficient of determination (R²) = 0.91; root mean square error (RMSE) = 0.11% and R² = 0.48; RMSE = 0.33, respectively). The local MLR models developed with both reflectance and TPI using values from all points showed high correlations and low prediction errors for SOC content (R² = 0.88, RMSE = 0.07%; R² = 0.79, RMSE = 0.06%, respectively). The comparison with an enlarged dataset consisting of all points from both fields (pooled approach) showed no improvement of the prediction accuracy but yielded decreased prediction errors. Lastly, the local MLR models were applied to the data of the respective other field to evaluate the cross-field prediction ability. The spatial SOC pattern generally remains unaffected on both fields; differences, however, occur concerning the predicted SOC level. Our results indicate a high potential of the combination of UAS-based remote sensing and environmental covariates, such as terrain attributes, for the prediction of topsoil SOC content at the field scale. The temporal flexibility of UAS offer the opportunity to optimize flight conditions including weather and soil surface status (plant cover or residuals, moisture and roughness) which, otherwise, might obscure the relationship between spectral data and SOC content. Pedologically targeted selection of soil samples for model development appears to be the key for an efficient and effective prediction even with a small dataset.

The Application of Digital Monitoring in Studying Soil Water Holding Capacity and Implications for Conservation Agriculture in the South-Western Siberia

The Kulunda Steppe is an example of soil degradation resulting from the intensive agricultural land use in the South Siberia. In this region, water is a limiting factor for crop production. Soil cultivation affects the soil’s physical properties, thus its water retention capacity. The study presents and discusses the results of measurements of the volume and availability of soil moisture at depths of 30cm, 60cm, and 120cm of loamy, low humus southern chernozems in the south of Western Siberia in the dry Kulunda Steppe during the 2013 and 2016 vegetation periods. We revealed some advantages of soil moisture conservation in the No-Tillage [NT] system compared with the system of deep tillage [DT]. At depths of up to 30 cm, there was a lower volume moisture level. Nevertheless, at depths of 60 cm, there was a higher moisture level in the NT system that could be considered a potential stock for individual crops during drought. Further measurements are needed to identify additional features of the NT soil conservation system.

Contribution of crop residue, soil, and fertilizer nitrogen to nitrous oxide emissions varies with long-term crop rotation and tillage

Agriculture is an important contributor to N2O emissions – a potent greenhouse gas – with high peaks occurring when soil mineral nitrogen (N) is high (e.g., after mineralization of organic N and N fertilizer application). Nitrogen dynamics in soil and consequently N2O emissions are affected by crop and soil management practices (e.g., crop rotation and tillage), an effect mostly assessed in the literature through comparisons of total N2O emission. Hence, information is scarce on the effect of these management practices on specific N sources affecting N2O emissions (i.e., N fertilizer, soil, above and belowground crop residues) – a knowledge gap explored in this study with the use of 15N tracers. The isotope approach enabled refinement on global N2O budget by directly determining the emission factors (EF) of above and belowground crop residues that vary in chemical composition and comparison with default EF values (e.g., IPCC EFs). Our experiment was conducted over the full-cycle of long-term crop rotations to (i) compare N2O totals and intensity, under no-tillage and conventional tillage, simple and diverse rotation; (ii) partition total N2O emissions into soil, N fertilizer, above and belowground crop residue N sources; (iii) compare the 12-month EF of crop residue against the default values proposed by IPCC (2019). For the tillage effect, annual N2O emissions were from 1.2- to 2.0-times higher on CT than NT soil due to 40% increased soil N derived N2O emission in CT. The diversified crop rotation emitted 1.3-times higher N2O than the simple rotation over the full-cycle of the rotations, but the effect was due to differences in N fertilizer rate between the rotations since emissions were equivalent when scaled by N rate. Finally, our results suggested that default IPCC EF are overestimated for crop residues under CT and NT, simple and diverse rotations as measured EFs never surpassed 0.1%.

Structure Stability of Cultivated Soils from Semi-Arid Region: Comparing the Effects of Land Use and Anionic Polyacrylamide Application

The Sustainable Development Goals of the United Nations call for applying soil management practices that contribute land degradation neutrality. Our objectives were to investigate the effect of (i) soil management—conventional tillage (CT under crop) and no-tillage (NT under grass)—and (ii) an amendment (polyacrylamide (PAM)) application on the structure stability indices of soils from a semi-arid region. Two sets of experiments were conducted using the high-energy moisture characteristic (HEMC) method for the assessment of (i) land-use type (CT vs. NT) in soils (30 samples) varying in texture, and (ii) the effect of six PAM concentrations (0, 10, 25, 50, 100, and 200 mg L−1) on three typical soils (sandy clay loam, clay loam, and clay) under CT management; then, the contributions of PAM concentration (CT) and NT were compared. Water retention curves of samples were obtained at a matric potential from 0 to −5.0 J kg−1 and characterized by a modified van Genuchten model that yields (i) model parameters α and n, and (ii) a soil structure stability index (SI). The treatments affected the shape of the water retention curves. Change of land use from CT to NT and PAM application to CT soil increased the SI and ɑ, and decreased n compared to CT-managed soils. The magnitude of the NT and PAM effect was inversely related to soil clay content. CT-managed soils treated with a low PAM rate (10–25 mg L−1) gave SI comparable to that obtained for the NT-managed soils, while CT-managed soils treated with a high PAM rate (50–200 mg L−1) yielded 1.3–2.0 and 2–4 times higher SI than that for NT and CT-managed soils, respectively. Our findings suggest that both the change of land use to NT or the addition of small amounts of PAM are viable alternatives for stabilizing CT-managed weakly alkaline semi-arid soils, whose soil structure stability is a priori limited.

Earthworms promote the accumulation of rhizodeposit carbon to soil macroaggregate in a Mollisol of Northeast China, primarily in long-term no-till soil

As soil ecosystem engineers, earthworms are the main promoters of soil aggregation, a process that drives the production of ecosystem services by soils. A crucial factor in the ecosystem service of carbon sequestration is rhizodeposit carbon, which is the main energy source of soil food webs. The effects of earthworms on the distribution of rhizodeposit-carbon in soil aggregates remain unclear. Here, we conducted a 13CO2 labeling experiment to determine the effects of earthworms on maize rhizodeposit carbon in soil aggregates after 14 years (2002–2016), in both conventional tillage (CT) and conservation tillage (no tillage, NT) soils. Four treatments were established in total: NTE (no tillage soil with earthworms), CTE (conventional tillage soil with earthworms), NTC (control, no tillage soil without earthworms), and CTC (control, conventional tillage soil without earthworms). Earthworms significantly enhanced the abundance of soil macroaggregates (>2000 µm and 250–2000 µm) on day 30 compared with day 2 (after labeling), especially in the NTsoils. On day 30, in the presence of earthworms, the amounts of rhizodeposit carbon in the >2000 µm and 250–2000 µm soil aggregates in the NTsoils were significantly higher than in those in the CTsoils (P <0.05), and higher δ 13C signatures in the same size aggregates were observed in the NT soils than in the CT soils (P<0.05). These findings indicated that compared with the CT soils, with the involvement of earthworm activity, the NT soils promoted more rhizodeposit carbon transformation to the soil macroaggregates. Our results clearly indicate that soil macroaggregates formed in different tillage soils in the presence of 2 different engineers (earthworms and roots) significantly differ from those formed in the presence of only one organism (roots) in the long term.

Parameters influencing run-off on vegetated urban soils: A case study in Marseilles, France

In urban areas, episodes of extreme precipitation may generate run-off floods, but urban soils are seldom considered in spatial planning documents. Our aim was to assess the infiltration of vegetated urban soils and to identify the soil parameters affecting infiltration in order to explore the potential of these soils for run-off mitigation under a Mediterranean climate with extreme precipitation episodes. We compared vegetated soils in the “urban” zone of the Marseilles’ 16th district (France) either lying on former clay quarries or tile factories (T) or not (NT) and with different land-uses. We used a simplified method to measure field saturated hydraulic conductivity (Kfs), measured penetration resistance in the first 0.15 m (Qd) and analysed physico-chemical properties in the first horizon. Levels of run-off production were estimated according to Kfs and an adaptation of USDA Hydrologic Soil Groups. All soils were Technosols or Anthrosols regardless of their prior history. We found that land-use history influenced Kfs, with T soils and soils with current vegetated land-use younger than 13 years having lower Kfs than NT soils and soils with land-use older than 13 years. Soil organic matter content influenced Kfs positively when soils were young, while vegetation cover and penetration resistance (most of the soils had Qd > 2 MPa) had not a clear effect on Kfs. Overall, combining Kfs and soil depth, 14.3% of the T soils and 84.6% of the NT soils had low levels of run-off production. It is therefore recommended that 1) Technosols or Anthrosols should be characterised for their unique physico-chemical and physical properties but also for their land-use history, and 2) the infiltration of these soils should be considered in spatial planning documents.

Diversified crop rotation with no‐till changes microbial distribution with depth and enhances activity in a subtropical Oxisol

AbstractSoil microbial community and enzyme activity regulate carbon and nutrient cycling in soils. No‐till has elevated levels of carbon at the soil surface compared to intensively tilled soils. The introduction of crop diversification in agricultural systems increases soil carbon protection and aggregate stability. Thus, the association of no‐till with crop diversification may change the soil microbial distribution and enhance activity in comparison with tilled soils with no crop diversification. We tested this hypothesis assessing the soil microbial community and enzyme activity in a long‐term (32 yr) experiment with contrasting soil management (no‐tillage, (NT) and conventional tillage (CT)) and cropping systems in southern Brazil. Long‐term NT increased microbial biomass at 0–5 cm. In contrast, soil microbial biomass was higher in deeper soil layers (10–30 cm) of CT. No‐tillage and crop diversification increased the activity of β‐glucosidase, acid phosphatase and N‐acetyl‐glucosaminidase. The benefits of an intensified/diversified crop rotation were offset by soil tillage. The higher abundance of PLFA groups at 0–5 cm and 10–30 cm of respective NT and CT soils were correlated with increased C and nutrient levels (N, Ca2+, Mg2+) and decreased Al3+.Highlights Crop diversification increased the soil microbial biomass and individual PLFA groups. No‐till without crop diversification did not change microbial biomass. No‐till with crop diversification increased enzyme activity. Subsoil fertility restricted microbial responses in a no‐till Oxisol.

Physical and chemical processes determining soil organic matter dynamics in a managed vertisol in a tropical dryland area

Vertisols are soils with a high potential for carbon (C) sequestration. However, these soils undergo swelling and shrinkage cycles, which exert a strong influence on soil organic matter (SOM) dynamics. The long-term effects of agricultural conservation practices on SOM content and stability on a Vertisol located in a tropical dryland area was evaluated.Two tillage systems (conventional tillage [CT], disc ploughing and extraction of 70% harvest residues, and no tillage [NT], incorporating 100% of the harvest residues) in combination with three different crop rotations (sorghum-soyabean [SrSy], maize-maize [MM] or soyabean-maize [SyM]) were tested. All plots were irrigated during dry periods. The effects on soil organic C, N, microbial biomass and aggregate size class distribution were evaluated. Carbon sink capacity were assessed by studying the aggregate-associated SOM content and quality (thermal recalcitrance), as determined by thermo-calorimetry.Relative to the CT system, NT yielded a higher percentage of small macroaggregates (2-0.25 mm). It also promoted the accumulation of aggregate-associated SOM, especially in the small macroaggregates and microaggregates. Thermal analysis revealed that the aggregate-associated SOM was more recalcitrant (higher values of T50 and more energy released at 475 °C) in NT than in CT. Coinciding with these effects, the soil microbial biomass/SOC ratio was lower in NT than in CT. The gain of SOM and the higher recalcitrance of OM in the NT soils may be related to different characteristics of NT Vertisols, such as poor aeration or disruption of the swelling and shrinkage cycles. The findings show that soil conservation practices increase the capacity for long-term C sequestration in Vertisols via organomineral interactions and SOM recalcitrance, which are determined by the formation of large cracks as a result of the swelling and shrinkage cycles that are some of the specific properties and processes of these soils.

Earthworms promote the accumulation of maize root-derived carbon in a black soil of Northeast China, especially in soil from long-term no-till

Recent studies have shown that earthworms regulate dynamics of plant litter and soil organic carbon. However, the effects of earthworms on rhizospheric carbon, which is the main energy source of soil food webs and a vital factor in soil carbon sequestration, remain unclear. Here, a 13CO2-labeling experiment was performed to determine the effects of earthworms on the fate of maize rhizodeposit carbon from black soil (Mollisol) following conventional tillage (CT) and 14 years (2002–2016) of conservation tillage (no-till, NT). A total of 4 treatments was established: NTE (no-till soil with earthworms), CTE (conventional till soil with earthworms), NTC (control, no-till soil without earthworms) and CTC (control, conventional till soil without earthworms). The results indicated that earthworms increased the amounts of root-derived in soils relative to the amounts in the corresponding no-earthworm control treatments. Maize biomass was significantly higher in the NTE treatment than in the CTE treatment (P < 0.05). Compared with the control treatments (NTC and CTC), the presence of earthworms stimulated maize biomass growth. On day 30 after labeling, the amount of rhizodeposit carbon in NT soil was significantly higher than that in CT soil (P < 0.05), and a higher δ13C signature in the soil organic carbon (SOC) was observed in the NTE treatment than in the CTE treatment (P < 0.05). These findings indicate that earthworms in NT soils were more likely due to the higher biomass inputs and were more likely to assimilate rhizodeposit carbon from roots than that in CT soils. We found that neither earthworm presence nor tillage significantly affected the δ13C signatures in the labile SOC fractions (dissolved organic carbon, DOC; microbial biomass carbon, MBC and particulate organic carbon, POC). Our results suggest that the presence of earthworm affects microbes and may increase the retention of rhizodeposit carbon. In the earthworm-worked soils, higher amounts of carbon were mineralized by soil microorganisms in the CT soil than in the NT soil. This finding demonstrates that earthworms in NT soils could promote the accumulation of rhizodeposit carbon. Our work highlights how earthworms in long-term NT soil facilitate photosynthesized carbon accumulation belowground.

Inter-annual changes in the aggregate-size distribution and associated carbon of soil and their effects on the straw-derived carbon incorporation under long-term no-tillage

Converting from conventional tillage to no-tillage influences the soil aggregate-size distribution and thus soil organic carbon (SOC) stabilization. However, the dynamics of soil aggregation and the straw-derived carbon (C) incorporation within aggregate fractions are not well understood. An experiment was established in 2004 to test the effects of two treatments, no-tillage with residue (NT) and conventional tillage without residue (CT), on the soil aggregate-size distribution and SOC stabilization in a continuous maize (Zea mays L.) cropping system located in the semiarid region of northern China. Soil samples were collected from the 0–10 cm layer in 2008, 2010 and 2015, and were separated into four aggregate-size classes (>2, 0.25–2, 0.053–0.25, and <0.053 mm) by wet-sieving. In each year, NT soil had a higher proportion of macroaggregates (i.e., >2 and 0.25–2 mm) and associated SOC concentration compared with CT. Additionally, to compare straw-derived C incorporation within NT and CT aggregate fractions, 13C-labeled straw was incubated with intact NT and CT soils. After 90 days, the highest proportion of 13C-labeled straw-derived C was observed in the >2 mm fraction, and this proportion was lower in NT than that in CT soil. Overall, we conclude that long-term continuous NT increased the proportion of macroaggregates and the C concentration within macroaggregates, and the physical protection provided by NT is beneficial for soil C sequestration in the continuous maize cropping system in semiarid regions of northern China.

Is chiseling or inverting tillage required to improve mechanical and hydraulic properties of sandy clay loam soil under long-term no-tillage?

Dynamic soil properties as affected by machine-soil interaction are potential indicators for the evaluation of management and traffic effects on soil structure. Our objective was to determine compressive, shear, and hydraulic soil properties in a sandy clay loam Hapludalf, under continuous no-tillage and tillage operations to ameliorate soil physical conditions. The studied tillage systems were long-term (13years) continuous no-tillage (NTc); chisel tillage two years before the experiment (CH2); inverting tillage performed on NT soil, 2years before and just-before the experiment (IT2,0); and chisel tillage performed on NT soil 3years before and just-before the experiment (CH3,0). Soil precompression stress, compressibility coefficient, cohesion, angle of internal friction, aggregate resistance, bulk density, porosity (total, macroporosity, microporosity), and water retention (field capacity, permanent wilting point, available water, and drainable water) were determined for 0.01–0.03m (surface) and 0.10–0.12m (subsurface) soil layers. The results show inverting and chisel tillage of soil previously under long-term no-tillage has little and/or short-lasting effect on soil composition and functional physical properties. Soil reconsolidation over time significantly affects soil structural condition. Thus, soil tillage is not need to improve soil structure of sandy clay loam subtropical soil. Furthermore, the terms capacity and intensity properties should not be used as synonyms to composition and functional properties, but they should rather be reserved to the thermodynamically basic quantity-intensity-capacity concept.

유기염소계 살충제 엔도설판이 토양세균 군집에 미치는 영향 평가

Although a global ban on the use of endosulfan, an organochloline insecticide, has taken effect in mid-2012, it has been still used in several countries, including India and China, and detected in diverse environments in the world due to its relative persistence and semi-volatility. In this study, the effect of endosulfan on soil bacterial community was investigated using 16S rRNA gene pyrosequencing method. When endosulfan was applied to an upland soil at a rate of 100 mg/kg soil (ES soil), the number of operational taxonomic units (OTU) and diversity indices for bacteria initially decreased and gradually recovered to the level of the non-treated soil (NT soil) during an eight-week incubation period. At bacterial phylum level, relative abundances of Proteobacteria and Verrucomicrobia were higher while those of Chloroflexi and Spirochaetes were lower in the ES soil than in the NT soil, suggesting that an endosulfan application affects the bacterial community structure in soil. In the ES soil, the relative abundances of the OTUs affiliated to the genera Sphingomonas and Burkholderia increased in the initial period of incubation while those affiliated to the genera Pseudonocardia and Opitutus increased in the late period of incubation. Because the first three genera contain bacterial strains reported to degrade endosulfan, they are expected to be involved in the degradation of endosulfan, probably one after another.

Exploring the relationships between soil fauna, different tillage regimes and CO2 and N2O emissions from black soil in China

Recent studies have shown that soil fauna can significantly affect greenhouse gas emissions. However, different functional groups and different soils can influence soil CO2 and N2O emissions to different extents. To date, little attention has been paid to whether soil fauna interactions with each other and their predators play a significant role in CO2 and N2O emissions under different tillage systems. Therefore, we studied how the interactions between soil fauna and their predators affect soil CO2 and N2O emissions from black soil following 13 years of conservation tillage (no-till) (NT) and conventional tillage (CT). We conducted a 35-day microcosm experiment with black arable soil and hay residue. The results indicated that the presence of earthworms and predator mites (EP) significantly increased the soil CO2 and N2O emissions in both NT and CT systems (P < 0.05). However, the addition of predator mites to microcosms with earthworms and Collembola treatments (ESP) did not significantly increase the soil CO2 (900.7 mg CO2-C kg−1 soil in NT, 991.0 mg CO2-C kg−1 soil in CT) or N2O (75.9 μg N2O-N kg−1 soil in NT, 79.0 μg N2O-N kg−1 soil in CT) emissions compared to earthworms and springtail (ES) treatments (CO2: 924.7 mg CO2-C kg−1 soil in NT, 914.4 mg CO2-C kg−1 soil in CT; N2O: 72.5 μg N2O-N kg−1 soil in NT, 251.4 μg N2O-N kg−1 soil in CT). Therefore, adding predators does not always increase the CO2 and N2O emissions, and the different body lengths of predators and the effect of predator-prey interactions on soil physicochemical properties should be considered. We found much higher dissolved organic carbon and nitrate availability in the E, ES and EP treatments at the time of high gas emissions on day 18, indicating that the major increase in CO2 and N2O emissions in these treatments may be due to enhanced denitrification. Our study indicates that under different tillage regimes, the interaction between soil fauna functional groups on the availability of C and N can decrease or increase soil CO2 and N2O emissions. Compared with CT soils, CO2 and N2O emissions from NT soils were lower, which demonstrates that long-term conservation tillage can reduce CO2 and N2O emissions from soil. The findings indicate that a more stable soil environment and food web with more intact functional groups are built in NT and may be more conducive to carbon and nitrogen sequestration for reducing soil CO2 and N2O emissions in the black soil region of Northeast China.

Kinetic to Saturation Model for Simulation of Soil Organic Carbon Increase to Steady State

Core Ideas We evaluated SOC dynamics in a long‐term soil tillage and N fertilization experiment. We proposed a kinetic to saturation model for long‐term simulation of SOC dynamics. The model was accurate in C‐depleted soils and accounted for SOC saturation process. The use of mathematical models predicting SOC dynamics can provide relevant information about the C storage potential of agricultural soils. We evaluated three mathematical models (first‐order kinetic, C saturation, and a proposed kinetic to saturation) predicting SOC dynamics and steady‐state SOC of a Hapludoll from central Kansas. The study was based on a long‐term experiment (17 yr) assessing soil tillage systems (chisel tillage [CT] and no‐till [NT]) and N fertilizer sources (168 kg N ha−1 as NH4NO3 [MF], cattle manure [OF], and a control treatment without N [CO]. The soil under NT (0–5 cm) had significant SOC accumulation (&gt;0.23 Mg C ha−1 yr−1) regardless of fertilization source, while the CT soil had negligible changes in SOC (&lt;0.12 Mg C ha−1 yr−1) without the addition of organic fertilizer as an external C source. Organic fertilization increased the original SOC by 56 and 192%, reaching steady state at 15.9 and 28.0 Mg ha−1 in CT and NT soils, respectively. The SOC predicted by all three models had significant correlations (r &gt; 0.80, p &lt; 0.05) with measured SOC. However, the C saturation model overestimated the measured SOC under C‐depleted conditions, failing RMSE and lack‐of‐fit tests, while the first‐order kinetic model overestimated NT OF steady‐state SOC by up to 58% in relation to the maximum SOC storage capacity determined for NT soils. The SOC predicted by the kinetic to saturation model agreed with both measured SOC and the maximum SOC storage capacity of NT soils. The kinetic to saturation model can be used for long‐term simulation of SOC dynamics in soils that are either C depleted or close to saturation.

Combined role of no-tillage and cropping systems in soil carbon stocks and stabilization

Increases in carbon (C) input and stabilization are key processes to turn soils into sinks of atmospheric CO2–C and help mitigating global warming. We hypothesized (i) that C sequestration in no-tillage soil is further enhanced by high input cropping systems and (ii) that the sequestered C is stored mainly in the mineral associated fraction. The objective of this study was to assess, in 2003, the C sequestration and stabilization in a subtropical Acrisol (Eldorado do Sul, Brazil) subjected to 18-year conventional tillage [CT] and no-tillage [NT] combined with two cropping systems: black oat (Avena strigosa Schreb) as winter cover crop – maize (Zea mays L.) as summer grain crop [Ot/M]; and black oat plus vetch (Vicia villosa Roth) as winter cover crops – maize in summer intercropped with cowpea (Vigna unguiculata (L.) Walp) cover crop [Ot+V/M+C]. Soil C stock in the 0–20cm layer was higher in NT than in CT, either in Ot/M (31.1 vs. 27.8Mgha−1, P<0.05) or Ot+V/M+C (37.3 vs. 32.8Mgha−1, P<0.05). Annual C sequestration rate in NT relative to CT was 0.25Mgha−1 in Ot+V/M+C and 0.18Mgha−1 in Ot/M, in agreement to the higher biomass-C addition and legume cover crops inclusion in Ot+V/M+C (7.6 vs 4.0Mgha−1 year−1) and to our first hypothesis. Increase in the proportion of large macroaggregates (9.51–4.76mm) and of mean weight diameter occurred in NT soil up to 10cm depth, both in Ot/M and Ot+V/M+C. In NT, most of the C accumulation relative to CT occurred in the mineral-associated fraction, showing the importance of organo-mineral interaction in C stabilization and supporting our second hypothesis. However, the physical protection by aggregates played equally important role by stabilizing the occluded particulate organic matter (occluded-POM) before it was further stabilized by organo-mineral interaction. No-tillage is recommended as a sustainable soil management, but to increase soil C accumulation, the potential of cropping systems such those based on legume cover crops must be concurrently explored.

Effects of tillage and crop rotation on soil microbial residues in a rainfed agroecosystem of northeast China

Agricultural management has significant impacts on soil microorganisms, which in turn influence soil relevant processes including soil organic matter (SOM) turnover. Amino sugars, as a microbial residue biomarker, are highly involved in microbial-mediated SOM cycling. However, the response of microbial-derived amino sugars to changes in soil management practices is poorly characterized in the arable soils (Typic Hapludoll, USDA Soil Taxonomy) in northeast China. The objective of this study was to assess the effects of soil tillage (conventional tillage CT vs. no tillage NT) and crop rotation (continuous corn ( Zea mays L.) monoculture vs. corn–soybean [ Glycine max (L.) Merr.] rotation) on the accumulation of amino sugars in this region. The following hypotheses were tested: (1) in an agroecosystem, tillage and crop rotation influence the accumulation of microbial residues in soils; (2) responses of fungal and bacterial cell wall residues to the practices are different, i.e., fungal-derived cell wall residues more benefited by no-tillage practices than bacterial. Implementation of no-tillage practices for 6 years significantly increased soil total amino sugars with an increase of 59% as compared with conventionally tilled plots ( P < 0.05). This highlights the positive effects of NT that promotes the accumulation of microbial-derived organic matter. The ratios of glucosamine to muramic acid in the NT soils across three soil depths significantly exceeded those in the respective CT soils due to a higher enrichment of glucosamine. This confirms our hypothesis that the microbial community shifted towards fungal dominance under NT and the phenomenon was more pronounced within the 0–5 cm layers. When NT systems were evaluated, the type of crop rotation used had a significant influence on the soil amino sugar content. Significant enrichment of total amino sugars (1042–1317 mg kg −1 soil) occurred in the continuous corn monoculture system as compared with the corn–soybean rotation field (943–1112 mg kg −1 soil) in the soil layers from 0 to −20 cm. Data obtained suggest that NT practices combined with continuous high C inputs can be adopted as an effective strategy to improve the cropland SOM in northeast China. Our results also indicate that it is possible to use amino sugars as an indicator to assess the changes in microbial community within a given ecosystem.

Postharvest nitrous oxide emissions from a subtropical oxisol as influenced by summer crop residues and their management

Nitrous oxide (N2O) is the most important non-CO2 greenhouse gas and soil management systems should be evaluated for their N2O mitigation potential. This research evaluated a long-term (22 years) experiment testing the effect of soil management systems on N2O emissions in the postharvest period (autumn) from a subtropical Rhodic Hapludox at the research center FUNDACEP, in Cruz Alta, state of Rio Grande do Sul. Three treatments were evaluated, one under conventional tillage with soybean residues (CTsoybean) and two under no-tillage with soybean (NTsoybean) and maize residues (NTmaize). N2O emissions were measured eight times within 24 days (May 2007) using closed static chambers. Gas flows were obtained based on the relations between gas concentrations in the chamber at regular intervals (0, 15, 30, 45 min) analyzed by gas chromatography. After soybean harvest, accumulated N2O emissions in the period were approximately three times higher in the untilled soil (164 mg m-2 N) than under CT (51 mg m-2 N), with a short-lived N2O peak of 670 mg m-2 h-1 N. In contrast, soil N2O emissions in NT were lower after maize than after soybean, with a N2O peak of 127 g m-2 h-1 N. The multivariate analysis of N2O fluxes and soil variables, which were determined simultaneously with air sampling, demonstrated that the main driving variables of soil N2O emissions were soil microbial activity, temperature, water-filled pore space, and NO3- content. To replace soybean monoculture, crop rotation including maize must be considered as a strategy to decrease soil N2O emissions from NT soils in Southern Brazil in a Autumn.

Microbial biomass and N cycling under native prairie, conservation reserve and no-tillage in Palouse soils

Tillage management practices that improve soil quality are needed to maintain agricultural productivity. Soil quality can be improved through increases in microbial biomass carbon (MBC) and the nitrogen (N) contents in different pools of soil organic matter (SOM). The objective of our experiment was to study the dynamics of MBC and N cycling in soils collected from the Palouse area of eastern Washington State. Soil managements were: no tillage for 4 (NT4) and 28 (NT28) years, conservation reserve program (CRP), native prairie (NP), and conventional tillage (CT). Microbial biomass carbon was 50% less in the CT soil than the NP soil and there was 74% less total soil N (TSN) in the surface CT soil compared to the NP soil. Conversion of CT to CRP, NT4, and NT28 increased MBC in the 0–5 cm depth by 40, 6 and 78%, respectively. Compared to CT, the TSN content was 20, 57, and 94% higher in CRP, NT4 and NT28, respectively. The net N mineralized (Nmin) over 180 days in the surface 5 cm was highest (69.5 µg N/cm 3) in NT28 soil and lowest (14.2 µg/cm 3) in CRP. Interestingly, the CT soil mineralized as much N as the NT systems but had less TSN than NT. Compared to NP, CT had a 70% reduction in particulate organic matter nitrogen (POM-N) to a depth of 20 cm. The conversion of CT soil to CRP, NT28, and NT4 enhanced the POM-N content by 65, 216, and 101% at 0–5 cm. The proportion of POM-N to TSN was lowest in CT soil whereas the NT and CRP soils were considerably higher. The lower Nmin/MBC ratios (qN) of the conservation systems imply a higher immobilization capacity and tighter soil N cycling. Mineralized N per unit of respiration (Nmin/CO 2-C) was highest in CT and NT28 management systems suggesting different factors were responsible in these systems for exhibiting almost similar values. The Nmin ratios along with MBC and POM-C relationships could be useful soil quality indicators in judging tillage-induced changes in soil management systems.