Soil Particulate Organic Matter Research Articles

Inundation impacts on diversified pasture biomass allocation and soil particulate organic matter stocks

AbstractNatural soil inundation caused by frequent and intense precipitation affects carbon allocation in grassland biomass, ultimately leading to changes in soil carbon storage. Increasing forage diversity could provide resiliency to inundation of grassland. The objective was to evaluate forage and root biomass and C and N stocks in the soil particulate organic matter (POM) from pastures under recurring short‐term inundation. Three forage species combinations were evaluated in an inundated (typically lasting for a few days after heavy rain events) and a non‐inundated pasture: (1) predominantly tall‐fescue (Festuca arundinacea Schreb.); (2) mixture of cool‐season perennials composed of tall‐fescue, orchardgrass (Dactylis glomerata L.), bluegrass (Poa pratensis L.) and white (Trifolium repens L.) and red clover (Trifolium pratense L.); (3) and cool‐season mixture of perennials overseeded with oats (Avena strigosa Schreb.) and rye (Secale cereale L.). Roots and forage biomass were sampled during the growing seasons of 2021 and 2022. Soil POM was evaluated 2.5 years after establishment. Inundation reduced forage and root biomass mainly during periods of higher inundation frequency, leading to lower C‐POM stocks (p < .05). Inundation caused a shift in the forage botanical composition, that is, higher occurrence of weeds and less productive grass species with shallow roots. The perennial cool‐season mixture did not increase forage yield compared with tall fescue only but did increase root mass. This occurred mainly at deeper layers and, consequently, increased C‐POM stocks (p < .05). Overseeding of winter annuals reduced overall forage production, despite increasing spring biomass when inundated in the first year, but reduced C and N‐POM stocks (p < .05). Perennial cool‐season forage mixtures can increase the resilience of pastures to inundation events and contribute to increased carbon sequestration in grasslands where inundation is prevalent.

Deciphering the role of particulate organic matter in soil nitrogen transformation in rice–rapeseed and rice–wheat rotation systems

Crop rotation affects the decomposition of soil organic matter (SOM) and thereby alter the composition of SOM fractions. It remains unclear how different SOM fractions impact soil nitrogen (N) transformation in various rotation systems. The aim of this study was to ascertain the role of particulate organic matter (POM)-a labile SOM fraction-in soil N transformation under various crop rotations. A paired plot experiment was conducted under two common cropping patterns, i.e., rice–rapeseed rotation (RR) vs. rice–wheat rotation (RW). Soil chemical composition and organic matter fraction before rice transplanting were compared between RR and RW systems after four years of crop rotations (2017–2021). With the same N inputs, the rice yield and N uptake under RR were 16.4 % and 13.2 % higher than those under RW, respectively. Compared with RW, RR resulted in higher carbon (C) and N contents in soil POM, despite minimal differences in total SOM. A larger potentially mineralizable N pool and a higher N mineralization rate occurred under RR than under RW, based on the results of soil net mineralization experiment. When POM was incubated alone, its contribution to potentially mineralizable N was 65.1 % and 61.3 % in RR and RW soils, respectively. Infrared spectroscopy revealed that in contrast with RW, RR promoted the accumulation of organic matter with high bioavailability (e.g., amides, carbohydrates, polysaccharides) in soil POM. This might be responsible for the higher gross mineralization and nitrification rates but lower gross immobilization rate under RR than under RW. Consequently, RR not only increased the contents of POMC and POMN but also improved the quality of POM fraction in soils. Findings of the present study demonstrate that POM plays a distinct role in soil N mineralization in various rotation systems. The discrepancy in POM content and composition resulting from various crop rotations leads to differences in soil N mineralization, which in turn affects the N supply and rice yield.

The Impact of Profile Genesis and Land Use of Histosol on Its Organic Substance Stability and Humic Acid Quality at the Molecular Level

This study is designed to evaluate soil organic matter (SOM) quality indicators: molecular indicators of dissolved organic matter (DOM) and hydrophobicity of humic acid (HA), distribution of quantity in humified and labile fractions of histosols during renaturalization. The aim is to determine the differences in the qualitative composition of humic acids at the molecular level, which are decided by the previous tillage and genesis, and to evaluate the impact of anthropogenization on the peat soil according to hydrophobicity, as well as to estimate the impact of soil genesis and removing peat layer. Soil samples were taken from the three Sapric Histosol (according to WRB2022) profiles and the 0–30 cm layer in three field replicates (Lithuania, Radviliskis mun.). Our study suggested that in the differently managed drained Sapric Histosol under renaturalization, the most significant changes occurred in the topsoil layer (0–30 cm), in which an increase in the content of SOM particles 106–2 µm in size. It is expedient to grow perennial grasses and legumes to maintain the soil organic carbon stability mobile humic acids to mobile fulvic acids ratio (MHA:MFA 0.83 to 0.86). An evaluation of the quality of HA (E4:E6) revealed their highest maturity in the unfertilized perennial grasses (3.88) and crop rotation (3.87) with grasses. The highest concentrations of hydrophilic groups (ratio of the C=O to O-H) were found in Sapric Histosol under deciduous hardwood forest (12.33). The lowest hydrophilicity (9.25 and 9.36) was of the crop rotation Sapric Histosol with removed peat layer. The most sustainable use of drained Sapric Histosol in the context of the sustainability and quality of its humus substances should be associated with the formation of perennial grass and clover grassland and the cultivation of deciduous hardwood. Therefore, the horizon forms on the top part of the profile, which protects deeper Histosolic material layers from its mineralization.

Aquatic biomass is a major source to particulate organic matter export in large Arctic rivers

Arctic rivers provide an integrated signature of the changing landscape and transmit signals of change to the ocean. Here, we use a decade of particulate organic matter (POM) compositional data to deconvolute multiple allochthonous and autochthonous pan-Arctic and watershed-specific sources. Constraints from carbon-to-nitrogen ratios (C:N), δ13C, and Δ14C signatures reveal a large, hitherto overlooked contribution from aquatic biomass. Separation in Δ14C age is enhanced by splitting soil sources into shallow and deep pools (mean ± SD: -228 ± 211 vs. -492 ± 173‰) rather than traditional active layer and permafrost pools (-300 ± 236 vs. -441 ± 215‰) that do not represent permafrost-free Arctic regions. We estimate that 39 to 60% (5 to 95% credible interval) of the annual pan-Arctic POM flux (averaging 4,391 Gg/y particulate organic carbon from 2012 to 2019) comes from aquatic biomass. The remainder is sourced from yedoma, deep soils, shallow soils, petrogenic inputs, and fresh terrestrial production. Climate change-induced warming and increasing CO2 concentrations may enhance both soil destabilization and Arctic river aquatic biomass production, increasing fluxes of POM to the ocean. Younger, autochthonous, and older soil-derived POM likely have different destinies (preferential microbial uptake and processing vs. significant sediment burial, respectively). A small (~7%) increase in aquatic biomass POM flux with warming would be equivalent to a ~30% increase in deep soil POM flux. There is a clear need to better quantify how the balance of endmember fluxes may shift with different ramifications for different endmembers and how this will impact the Arctic system.

Detection of biofilm and planktonic microbial communities in litter/soil mixtures

Microbial community of the soil can be subdivided into a planktonic community of motile organisms and a community of sessile organisms, including those constituting biofilms on physical surfaces of different texture. Biofilm communities on surfaces of organic particles represent a crucial factor involved in decomposition of plant litter and soil particulate organic matter in general. In spite of their great ecological importance, the composition of soil biofilm communities is only scarcely studied due to methodological problems connected with distinguishing biofilm inhabitants from other soil organisms.In this study, we were able to distinguish microbial communities colonizing four compartments of the experimental system: particles of the litter/soil mixture, biofilms on adjacent smooth or fibrous glass surfaces, and plankton. Existence of different preferences of microbial operational taxonomic units (OTUs) to occupy the experimental compartments has been suggested on the basis of their relative abundance in the community. Three main OTU groups have been defined according to these preferences. They are tentatively termed generalists, OTUs corresponding to organisms preferring the litter particles and OTUs corresponding to selective organisms discriminating between different surface types. At the same time, temperature has been identified as a factor influencing the switching between preferences of organisms for experimental compartments. Our work contributes to the description of the spatial microscale distribution of microorganisms in soil containing decomposing organic matter.

Anthropogenic and Natural Influences on Soil Organic Carbon Fractions: A Case Study on Soils of Meyghan Lake in Arak, Iran

Monitoring and assessment of soil organic carbon (SOC) in the soils of arid areas are very important. The objectives of the study were to evaluate the responses of extractable and particulate organic matter in soils around Meyghan Lake in Arak (Iran) to surface water-inflows. Two layers (0-30 cm and 30-60 cm) of soils were sampled in the release sites of municipal wastewater and 3 rivers. Different fractions of SOC were measured and statistically analyzed. The soil sampled from the release sites of municipal wastewater had the highest total organic carbon (14.1 mg TOC g-1 topsoil) and free particulate organic matter (8.07 mg FPOM g-1 topsoil) due to better soil condition for plant growth. In contrast, the soil sampled from the release sites of wastewater of sodium sulfate plant had the lowest the total organic carbon (3.50 mg TOC g-1 topsoil) and all of the fractions. The cold water extractable OC (CWEOC), occluded particulate organic matter (OPOM) and the heavy fraction (HF) as slow fractions responded to soil sampling time better than active fractions. They significantly increased in the soils sampled in fall. The means of CWEOC, hot water extractable OC (HWEOC) and OPOM were higher in the soils sampled from the eastern part of the lake with higher clay and moisture contents and lower elevation. They responded better to the soil properties controlling the biological activity and biodegradation. The best fraction for the study of short-term changes of SOM by anthropogenic and natural effects was FPOM in these non-agricultural lands.

Changes in particulate and mineral-associated organic carbon with land use in contrasting soils

Soil organic carbon (SOC) is the largest terrestrial carbon (C) stock, and the capacity of soils to preserve organic C (OC) varies with many factors, including land use, soil type, and soil depth. We investigated the effect of land use change on soil particulate organic matter (POM) and mineral-associated organic matter (MOM). Surface (0−10 cm) and subsurface (60−70 cm) samples were collected from paired sites (native and cropped) of four contrasting soils. Bulk soils were separated into POM and MOM fractions, which were analyzed for mineralogy, OC, nitrogen, isotopic signatures, and 14C. The POM fractions of surface soils were relatively unaffected by land use change, possibly because of the continuous input of crop residues, whereas the POM fractions in corresponding subsurface soils lost more OC. In surface soils, MOM fractions dominated by the oxides of iron and aluminum (oxide-OM) lost more OC than those dominated by phyllosilicates and quartz, which was attributed to diverse organic matter (OM) input and the extent of OC saturation limit of soils. In contrast, oxide-OM fractions were less affected than the other two MOM fractions in the subsurface soils, possibly due to OC protection via organo-mineral associations. The deviations in isotopic signature (linked with vegetation) across the fractions suggested that fresh crop residues constituted the bulk of OM in surface soils (supported by greater 14C). Increased isotopic signatures and lower 14C in subsurface MOM fractions suggested the association of more microbially processed, aged OC with oxide-OM fractions than with the other MOM fractions. The results reveal that the quantity and quality of OC after land use change is influenced by the nature of C input in surface soils and by mineral-organic association in subsurface soils.

An Arboriculture Treatment of Biochar, Fertilization, and Tillage Improves Soil Organic Matter and Tree Growth in a Suburban Street Tree Landscape in Bolingbrook, Illinois, USA

Background: Urban tree growth may be reduced due to poor urban soil conditions. Soil management to alleviate poor urban soil conditions often includes organic amendments, fertilization, and/or tillage. A 3-year experiment was conducted in an urban landscape in Bolingbrook, Illinois, USA, to test whether an arboriculture treatment with biochar, fertilization, and tillage could improve soil quality and tree growth. Methods: The urban landscape included 75 street trees (Gleditsia triacanthos, Ulmus parvifolia, and Acer rubrum) growing in compacted, fine-textured soils. Results: The results of this experiment suggest that the arboricultural treatment of biochar, fertilization, and tillage (BFT) may improve soil quality and urban tree growth. Relative height growth was significantly greater (P ≤ 0.05) for Acer rubrum trees with BFT treatment (+ 28.9%) compared to tillage alone (+ 13.3%). Total soil organic matter (SOM), particulate soil organic matter (POM), and a soil quality index (SQI) were significantly (P ≤ 0.05) greater in the BFT treatment (total SOM = 6.00%, POM = 9.73%, and SQI = 70.2) compared to the tillage treatment (total SOM = 5.29%, POM = 7.23%, and SQI = 60.8). The SOM responses to the BFT treatment appear to be relatively short-lived but correlated with measures of tree growth. Conclusion: This arboricultural treatment of biochar, fertilization, and tillage has potential to be used to improve soil quality and promote growth for trees growing in compacted, fine-textured soils in suburban street tree landscapes.

Mechanisms controlling the stabilization of soil organic matter in agricultural soils as amended with contrasting organic amendments: Insights based on physical fractionation coupled with 13C NMR spectroscopy

Soil organic matter (SOM) has vital roles in the global carbon (C) cycle and the use of organic amendments (OAs) to maintain or improve SOM levels is a promising practice. However, the mechanisms underlying SOM stabilization in OA-amended soils remain insufficiently resolved. For more effective understanding on such issues, we examined soil samples from a long-term experimental plot (26–31 years) that included six treatments, namely, a chemical fertilizer (CF) alone (CF), a bark compost plus CF (BC + CF), a coffee residue compost plus CF (CRC + CF), a cattle manure compost plus CF (CMC + CF), and a cattle manure (CMC) or sewage sludge compost (SSC) alone at a higher application rate, using physical fractionation. In the fractionation, free particulate SOM (fSOM), free SOM occluded in aggregates (oSOM), and SOM weakly bound to minerals (wSOM; s.g. 1.6–2.0 g cm−3) and strongly (sSOM; s.g. >2.0 g cm−3) were separated and characterized using 13C nuclear magnetic resonance (NMR) along with OAs and bulk soil samples. The long-term OA applications enhanced the total C accumulation and the amount of C accumulated as oSOM, wSOM, and sSOM correlated positively with the total C content. The application of BC or CRC resulted in a greater accumulation of fSOM. Conversely, the continuous application of SSC or CMC, which has a high N content and a low C/N ratio, led to a greater accumulation of C, mainly as wSOM. Our findings suggest that both the quality and quantity of OAs control the forms of C that accumulate and this involves different mechanistic pathways. We suggest that the abundant alkyl C in the wSOM and sSOM fractions was SSC-derived SOM in the SSC soil while in the case of the CMC soil, this was due to the increased contribution of microbial-derived SOM.

Formation efficiency of soil organic matter from plant litter is governed by clay mineral type more than plant litter quality

Plant litters incorporated in soils are decomposed by microorganisms and partially transformed into soil organic matter (SOM) through mineral-organic association and physical protection in soil aggregates. Few studies have linked the effects of clay mineralogy and plant litter quality on controlling the formation efficiency of SOM. Using model soils, the objectives of this study were (1) to determine the effects of clay mineral type and plant litter quality on soil respiration dynamics, and formation efficiency of SOM, physical fractions, and chemical and microbial compositions of SOM at the end of a 120-day incubation; (2) to unravel SOM protection mechanisms and extents by specific clay minerals; and (3) to understand the key role of clay minerals relative to plant litter quality in controlling SOM formation. The changes in X-ray diffraction peak intensity (in terms of peak height) of the clay minerals during incubation and after H2O2 treatment provided evidence for surface adsorption by vermiculite and pore entrapment by kaolinite and illite assemblages. The SOM protection extent parameter, defined based on accumulative soil respiration dynamics, explained well the variation of the formation efficiency of mineral associated SOM (MAOM) and, to a lesser extent, that of occluded particulate SOM (oPOM) in aggregates. 90–96% of plant litter-derived C was protected in the vermiculite material and 33–60% in the pure kaolinite and illite materials. The pure vermiculite material showed the greatest fractions of MAOM and oPOM, the highest relative abundances of O–alkyls and anomeric from carbohydrates in the MAOM fraction. < 1% of plant litter-derived C was transformed into microbial biomass and residues, and fungal residues only were associated with the pure vermiculite material. These results suggested that plant litter incorporated into the soil was decomposed mainly through the ex vivo modification pathway and transformed into SOM through both mineral-organic association and physical protection pathways. Plant litter-derived C was likely protected through mineral-organic association from the earlier stages of decomposition by vermiculite than kaolinite and illite, resulting in more plant carbohydrates associated with vermiculite. Therefore, clay minerals determined SOM formation pathways and played a greater role in controlling SOM formation efficiency than plant litter quality.

The path less taken: Long-term N additions slow leaf litter decomposition and favor the physical transfer pathway of soil organic matter formation

Understanding soil organic matter (SOM) formation as a balance between soil microbial access to organic plant inputs and protection by chemical recalcitrance and mineral associations can greatly improve our projections of this important terrestrial carbon pool. However, gaps remain in our understanding of the processes controlling the formation and destabilization of SOM and how these processes are affected by persistent global changes, such as nitrogen (N) deposition. To assess how elevated N deposition influences decomposition dynamics and the fate of plant inputs in a temperate deciduous forest, we coupled a reciprocal transplant leaf litter decomposition study with an analysis of the distribution of SOM in mineral associated and particulate organic matter fractions at a long-term, whole-watershed, N fertilization experiment. Nearly 30 years of N additions slowed leaf litter decomposition rates by about 11% in the fertilized watershed, regardless of the watershed from which the initial litter was collected. An apparent consequence of the altered rates of decomposition was that the proportion of SOM in light particulate organic matter in soil from the fertilized watershed was about 40% greater than that of the reference watershed, and was positively correlated with the bulk soil carbon to nitrogen ratio. Collectively, our results suggest that N saturation in a temperate forest alters SOM formation by slowing decomposition and favoring the accumulation of particulate organic matter as opposed to microbially processed mineral associated organic matter.

Pore architecture and particulate organic matter in soils under monoculture switchgrass and restored prairie in contrasting topography

Bioenergy cropping systems can substantially contribute to climate change mitigation. However, limited information is available on how they affect soil characteristics, including pores and particulate organic matter (POM), both essential components of the soil C cycle. The objective of this study was to determine effects of bioenergy systems and field topography on soil pore characteristics, POM, and POM decomposition under new plant growth. We collected intact soil cores from two systems: monoculture switchgrass (Panicum virgatum L.) and native prairie, at two contrasting topographical positions (depressions and slopes), planting half of the cores with switchgrass. Pore and POM characteristics were obtained using X-ray computed micro-tomography (μCT) (18.2 µm resolution) before and after new switchgrass growth. Diverse prairie vegetation led to higher soil C than switchgrass, with concomitantly higher volumes of 30–90 μm radius pores and greater solid-pore interface. Yet, that effect was present only in the coarse-textured soils on slopes and coincided with higher root biomass of prairie vegetation. Surprisingly, new switchgrass growth did not intensify decomposition of POM, but even somewhat decreased it in monoculture switchgrass as compared to non-planted controls. Our results suggest that topography can play a substantial role in regulating factors driving C sequestration in bioenergy systems.

Soil Particulate and Mineral-Associated Organic Matter Increases in Organic Farming under Cover Cropping and Manure Addition

This study aimed to investigate the soil organic carbon (SOC) sequestration rate and soil organic matter (SOM) composition in conventional rotational cropping with mineral fertilization compared with organic cover cropping with and without composted manure addition during 2008–2018 to specify the SOM stabilization under different farming systems. The SOC proportion in particulate organic matter (POM) (63–2000 µm) and mineral-associated organic matter (MAOM) (&lt;63 µm) fractions were estimated in different treatments, and the SOM composition in the fractions was characterized by FTIR spectroscopy. The SOC sequestration rate was treatment-dependent, with the higher SOC sequestration rate (1.26 Mg ha−1 y−1) in the organic treatment with cover crop and composted manure. Across all treatments, 57.3%–77.8% of the SOC stock was in the MAOM fraction. Mineral N fertilization increased POM-C concentration by 19%–52% compared with the unfertilized control. Under the organic treatments, the POM-C concentration was 83%–95% higher than the control. The MAOM-C concentration increased by 8%–20%. The mineral N fertilization and organic treatments (with and without cover crops and composted manure) increased the SOC stock proportion of POM. The highest proportion of SOC stock related to POM was in the cover cropping system, reducing the proportion of C related to the MAOM fraction, but the addition of composted manure with cover cropping also increased the proportion of C in MAOM. Compared with MAOM, the POM had a less resistant organic matter composition, and the POM resistance was higher in organic than conventional treatments. In general, the recalcitrance of SOM increased with SOC concentration. The POM fraction had higher aromaticity (or degree of decomposition) than the MAOM fraction. The aromaticity in POM and MAOM fractions was higher in the organic farming system and depended on mineral N fertilization and cover cropping, but the effect of manure was not significant. Although the SOC sequestration rate was higher under manure addition, resulting in the highest formation of both POM and MAOM in the soil, manure addition had little effect on overall SOM composition compared with cover crops.

Bioenergy production effects on SOM with depth of loblolly pine forests on Paleaquults in southeastern USA

Managed loblolly pine (P. taeda L.) forests comprise a major land-use across the “wood basket” of the southeastern US. Lower coastal plain loblolly pine forests can enhance carbon (C) storage in fast-growing vegetation and soils, representing a significant opportunity to manage these forests for improved soil health through an understanding of soil C and nitrogen (N) storage. Furthermore, these forests have unrealized potential to produce biomass for emerging bioenergy markets. Despite this, very little is known about how intensified management (herbaceous bioenergy production) of these forests influences short-term soil organic C (SOC) and soil organic N (SON) pools in surface and subsurface soil horizons. The field site was located in the Lower Coastal Plain of North Carolina, USA in which trees were planted in bedded (e.g., raised) rows (bed) and intercropped with or without switchgrass (P. virgatum L.) between the bedded rows of trees (interbed). Soils were collected from four depths (0–5, 5–15, 15–30, and 30–45 cm) and two locations (bed and interbed regions) and fractionated into light and heavy mineral-associated SOC and SON pools using a sequential density fractionation technique. Bulk soil SOC and SON concentration as well as C:N ratio decreased with depth for both treatments, while 15N became enriched. Free and occluded lighter fractions (< 1.65 g cm−3) had higher SOC and SON concentration (~45% C and ~ 1.15% N) compared to medium (1.65–2.00 g cm−3) and heavy (> 2.00 g cm−3) fractions. At the 0–5 cm depth in interbeds, SOC and SON were concentrated in the free light fraction (~45%), but transitioned to being concentrated in the heaviest mineral-associated fraction at the 15–30 (~55%) and 30–45 (~70%) cm depth. The 15N analysis of density fractions indicated progressive enrichment with increasing density, suggesting increasing incorporation of microbially-derived products into stable mineral-associated soil organic matter (SOM) pools. In the pine-switchgrass treatment, SOC and SON concentrations were higher in the light and medium fractions in beds and interbeds compared to the pine only treatment, particularly at the 30–45 cm depth. The C:N ratio in the pine-switchgrass treatment was higher compared to the pine only treatment indicating inputs of new plant-derived organic matter. Furthermore, the δ13C stable isotope signature was enriched in both the occluded light fraction (1.65 g cm−3) and the mineral-associated fraction (1.65–1.85 g cm−3). Our results suggest that switchgrass intercropping is contributing to the early buildup of SOM in particulate and mineral-associated SOM pools possibly through additions of new root-derived organic matter and the positive effect on soil microbial activity through priming of microbes.

Soil structure as a significant indirect factor affecting crop yields

Soil structure as a significant indirect factor affecting crop yields

Frequent Fire Reduces the Magnitude of Positive Interactions Between an Invasive Grass and Soil Microbes in Temperate Forests

Fire activity is increasing in many regions. Although increased fire activity is expected to promote plant invasion, over longer time periods, frequent fire can shift the nutrient status of ecosystems, which may alter interactions between invasive plants and soil microbial decomposers. Here, we applied a fire treatment to plots embedded in deciduous forests under regimes of either fire exclusion or frequent fire and invaded by the most widespread invasive grass in the eastern USA (Microstegium vimineum) to determine how frequent fire affects plant–soil interactions while controlling for time after fire. We predicted that frequent fire would increase microbial nitrogen (N) limitation, leading to lower Microstegium productivity and reduced soil carbon (C) and N loss. We found that Microstegium leaf, root, and microbial biomass C/N ratios were significantly wider under frequent fire than fire exclusion. Consistent with these patterns, dissolved organic N concentration was 22% lower and the activity of an exoenzyme targeting N acquisition was 59% higher under frequent fire, indicating that frequent fire increased microbial N limitation. Higher surface soil C and N and fire-induced increases in particulate soil organic matter N suggest that frequent fire in these grass-invaded forests enhanced microbial N limitation through the accumulation of microbially resistant pyrogenic N. A structural equation model confirmed that these changes were interrelated and associated with 87% lower Microstegium aboveground biomass and 85% higher fine root biomass. These findings provide new insights into how frequent fire impacts plant–soil microbial interactions and thus may feedback to plant invasion over longer time periods.

Changes in soil fungal community on SOC and POM accumulation under different straw return modes in dryland farming

ABSTRACT We conducted a 2.5-year field experiment to test the effects of straw incorporated evenly into the soil (EIS) on soil fungal community, SOC chemical composition, and particulate organic matter fractions via comparing with no straw returning (CK), straw mulching (SM), straw plowed into the soil (SP), and identified the linkages between soil fungal community as well as organic C accumulation and POM formation. Our results showed that EIS treatment significantly increased the concentrations of SOC and the proportion of carbohydrate C, di-O-alkyl C, and O-alkyl C in SOC structure, increased the mass proportion and OC contents of MA(c)POM and mM-POM in the upper 40 cm of soil. Meanwhile, EIS treatment increased the relative abundance of Ascomycota, Zygomycota, Chytridiomycota, and Dothideomycetes in 0–20 cm depths, and also had the highest relative abundance of Glomeromycetes and Dothideomycetes in the 20–40 cm soil. Also, our study suggests that straw return enhanced the relative abundances of fungi involved in the carbon cycle and sequestration, including Zygomycota, Chytridiomycota, and Glomeromycota, and Ascomycota. The shifts in fungal community structure can accelerate organic C accumulation and the formation of soil particulate organic matter, especially in EIS treatment.

Characterizing mass–volume–density–porosity relationships in a sandy loam soil amended with compost

Although compost is widely used as an organic soil amendment or conditioner, little is known of how it affects the characteristics or interactions among soil constituents. To address this, mixture theory was used to describe the mass–volume–density–porosity attributes and interactions among bulk soil, the mineral constituent, and the organic matter constituent of a sandy loam soil in a no-till corn field that had received one-time additions of yard waste compost at rates of 0 (control), 64, 154, and 380 dry t ha−1. Bulk density (BD, 0–10 cm depth) decreased consistently and near-linearly with increasing soil organic matter (SOM) mass fraction (FOM) for all six growing seasons (2012–2017) after compost addition. Fitting mixture theory expressions to BD vs. FOMdata and to soil particle density vs. FOMdata for 2013–2017 yielded constant mineral and SOM self-packing densities of DM = 1.673 Mg m−3and DO = 0.335 Mg m−3, respectively, and constant mineral and SOM particle densities of ρM = 2.760 Mg m−3and ρO = 1.409 Mg m−3, respectively. On a self-packing basis, soil mineral and SOM domain porosities were constants at nM = 0.39 and nO = 0.76, respectively. On a bulk soil volume basis, soil mineral and SOM porosities and volume ratios were linear functions of FOM. The porosity and volume characteristics of the SOM domain differed substantially from those of bulk soil and the mineral domain, and may therefore control the agri-environmental performance of soil, given that organic matter influences soil functioning more than mineral matter.

Soil particle density as affected by soil texture and soil organic matter: 1. Partitioning of SOM in conceptional fractions and derivation of a variable SOC to SOM conversion factor

Soil particle density (ρS) is one of the basic physical properties of soils and represents an essential element of diverse pedotransfer functions (PTFs). Recent findings support a PTF where the solid soil particles were considered as a mass-based mixing ratio of two components, soil mineral substance (SMS) and soil organic matter (SOM), which are related to the corresponding component particle densities. In this study, we developed a hierarchically structured model considering the subcomponents of SMS and SOM that are based on soil characteristics recorded by routine soil inventories - soil texture and soil organic carbon (SOC). Regarding SOM, we were faced with the problem that both the SOC to SOM conversion factor and the SOM particle density are variable. Finally, we generated a mechanistic approach to predict the particle density of soils as affected by subfractions of both soil mineral substances and soil organic matter. For the model calibration, related literature provided the required boundary conditions. We calibrated our model on a dataset (N = 501) from locations worldwide covering the full range of possible soil organic matter contents, diverse textures and soil parent materials. In the results, we quantified i) the SOC dependency of the SOC to SOM conversion factor as well as of the SOM subfraction’s particle densities and ii) the mean particle densities of the clay-, silt- and sand-size fractions.

Soil chemical properties after 12 years of tillage and crop rotation

AbstractCrop rotation in combination with tillage can improve productivity, enhance economical return, and reduce soil erosion. The objective of this study was to evaluate the impact of moldboard plow (MP), strip tillage (ST), no‐tillage (NT), and crop rotations on: (1) crop yield; (2) soil chemical properties; and (3) particulate organic matter (POM). The study was initiated in 2007 at the University of Nebraska‐Lincoln Panhandle Research and Extension Center near Scottsbluff, NE. Crops in rotation were corn (C; Zea mays L.) and dry bean (DB; Phaseolus vulgaris L.) organized in a 3‐yr rotation (C–DB–C) and a 4‐yr rotation with the addition of sugar beet (SB; Beta vulgaris L.) (C–DB–C–SB) such that each phase of the rotation was present each year. Soil samples collected from the surface 20 cm in the spring of 2019 were analyzed for POM and soil chemical properties. Crop yields were influenced by the previous crop, but not by tillage, except for sugar beet. The 2018 corn yield following dry bean exhibited the highest yield (15.6 Mg ha−1) compared with corn following corn or sugar beet. Soil chemical studied were not influenced by tillage or crop rotation. Corn in rotation enhanced soil organic matter (SOM) by 22% and soil organic carbon (SOC) by 28% in corn in the 3‐yr rotation compared with corn in the 4‐yr rotation. Surface soil POM was 32% higher with NT than MP and 17% higher in ST than MP. Alternative management strategies need to be implemented to maintain land sustainability in rotation with sugar beet and dry bean.