Increased Aggregate Stability Research Articles

Short-term service crops affect the spatial organization of soil aggregates, microbial C[sbnd]N biomass, and microbial activities in a degraded monoculture system

Service crops are grown to provide ecosystem services, such as the ability to increase soil organic matter and fertility. Also, they reduce erosion processes, weed control, disease regulation, water purification, soil biodiversity, and physical restoration. The physical arrangement of elemental particles in soil aggregates controls many ecosystem functions such as soil stability and carbon sequestration. This study aimed to analyze the short-term effect of including different service crops on the soil aggregate dynamics in a degraded common bean monoculture system and how it influences the rhizospheric microbial activity, carbon, and nitrogen microbial biomass. Here, we measured soil water-stable aggregates, particulate and associated organic carbon, soil microbial biomass, microbial activity, service crop aerial biomass, and cash crop yield in bulk soils during the 2020/2021 and 2021/2022 agricultural cycles. Soil samples from depths of 0–10 cm from five management treatments (annual service crop/common bean) were analyzed under no-tillage: 1) Oat (O) = Avena sativa/common bean; 2) Wheat (W) = Triticale/common bean; 3) Vetch (V) = Vicia villosa/common bean; 4) Melilotus (Me) = Melilotus alba/common bean; 5) common bean monoculture (M) = common bean without service crop. Additionally, two controls were analyzed: 6) Brachiaria perennial (BP) = Brachiaria brizantha perennial; 7) Native vegetation (NV). Service crops significantly increased aggregate stability, mean weight diameter, particulate matter and associated organic carbon, promoting the formation of large macroaggregates (0.25–2 mm and > 2 mm). This led to an increase in carbon stocks. Microbial activity expressed as hydrolysis of fluorescein diacetate and acid phosphatase activity, increased in the largest fraction for all service crops. Vicia improved surface residues; on average all service crops increased the common bean yield by 107.25 %. In summary, Vicia represents the best alternative as a service crop to improve the quality and health of degraded monoculture soils.

Soil type regulates the divergent loss characteristics of sediment associated carbon and nitrogen in different size classes during rainfall erosion on cultivated lands

Sediment associated carbon and nitrogen loss under rainfall, an important cause of soil quality degradation and water eutrophication, strongly depends on the intrinsic properties of original soil types. Relative to total loss, the transport behaviors of organic carbon and nitrogen among sediment size classes and response to soil types remain poorly understood. The concentrations of organic carbon (OC) and total nitrogen (TN) in different sediment size classes (>1, 0.25–1, 0.10–0.25, and <0.10 mm) and their contributions to total sediment load during rainfall erosion were determined under field plot rainfall simulation (at 90 mm h−1) on three contrasting soil types (Luvisol, Alisol and Ferralsol) with increased aggregate stability. During rainfall erosion, the concentrations of OC and TN in total and different sized sediments decreased first and then reached a steady state. The variability of OC and TN concentrations (coefficient of variations in 4.2–53.1% and 6.6–41.9%) among sediment size classes decreased from Luvisol to Ferralsol. Compared to original soils, sediments exhibited larger C/N ratios for Luvisol, and smaller values for Alisol, indicating the more selective transport of labile organic matter for weaker aggregated soils. Among sediment size classes, fine particles (<0.10 mm) accounted 69–88% of total OC and TN losses for Luvisol, and decreased to 30–39% for Ferralsol; and the main transport mechanisms of sediment associated OC and TN shifting from suspension-saltation (<0.10 mm) to rolling (>0.25 mm) with increased aggregate stability. Among original soil properties, inorganic cementing agents (including amorphous iron oxides and clay minerals) showed closer relationships with sediment OC and TN losses (|r| = 0.61–0.89, p < 0.001) than organic matter properties (|r| = 0.55–0.87, p < 0.001), further implying the important role of soil aggregate stability across soil types. This study provides an in-depth understanding on soil carbon and nitrogen losses and their divergent characteristics among soil types deserves consideration in the development of erosion model and land management in agricultural systems.

Enhancing soil resilience in Iranian Haploxeralfs: A study on the impact of two organic matters on aggregate stability and mechanical resistance

In arid regions around the world, erosion is a frequent occurrence due to low annual rainfall weakening plants, which in turn affects the concentration of soil organic matter (SOM). When the soil is exposed, sudden and heavy rainfall can lead to soil degradation, particularly in soil with high sodicity where unstable aggregates are easily ruptured, initiating the first phase of soil erosion. To investigate this phenomenon, soil samples were collected from an erosion‐prone area near Maharloo Salt Lake, specifically Chah‐angiri (soil 1) and Kamal-abad (soil 2), which are loam and silty clay loam soils with low SOM.&lt;strong&gt; &lt;/strong&gt;To evaluate the effect of organic matter sources on soil stability, cow manure (animal source) and wheat straw (plant source) were applied to both soil samples at four different rates (0.0, 10.0, 20.0, and 40.0 g kg&lt;sup&gt;−1&lt;/sup&gt;) and incubated for four months. The soil’s aggregate stability and mechanical resistance were then assessed using two different methods: mechanical resistance, which was measured as the module of rupture and penetration resistance, and aggregate stability, which was evaluated using the conventional and Le Bissonnais methods.&lt;strong&gt; &lt;/strong&gt;The application of organic matter resulted in a linear increase in aggregate stability in both soils, with the increase in Chah‐angiri (with lower sodicity) being greater than Kamal‐abad (with higher ESP). Both linear and exponential equations showed that organic matter treatment reduced soil mechanical resistance exponentially, with wheat straw proving more effective than cow dung at stabilizing aggregates against slaking and lowering soil mechanical resistance in both soils.&lt;strong&gt; &lt;/strong&gt;Furthermore, the stability of aggregates changed by mechanical breakdown (MWD&lt;sub&gt;stir&lt;/sub&gt;) was found to have the strongest relationship among three Le Bissonnais treatments (MWD&lt;sub&gt;slow&lt;/sub&gt;, MWD&lt;sub&gt;fast&lt;/sub&gt;, and MWD&lt;sub&gt;stir&lt;/sub&gt;) and the aggregate stability test using the usual technique (Kemper and Rosenau). The organic matter rate had a significant effect (&lt;em&gt;P &lt;/em&gt;&amp;lt; 0.001) on MWD&lt;sub&gt;stir&lt;/sub&gt;, which increased with rate in a linear relationship (&lt;em&gt;r&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; = 0.957, &lt;em&gt;P &lt;/em&gt;= 0.022). Finally, the stability of soil aggregates in water was also investigated.

Assessment of soil aggregate pore structure after 8 years of cultivation from the parent material of a Mollisol

Soil erosion exposes the underlying parent material (PM) to the surface and an appropriate soil restoration approach is required to maintain soil quality. However, the current knowledge on soil restoration (e.g., improvement of soil aggregate structure) is mainly obtained from studies on well-developed soils. It remains unclear how aggregate pore structure of soils can be improved following different agricultural practices during the early stage of pedogenesis. The present study quantified the effects of 8 years of different agricultural practices (land use types, mineral fertilizers, and different amounts of organic inputs) on the aggregate stability, aggregate pore morphology, and surface properties of a topsoil (0–20 cm) and compared the findings with those of a prior PM and a long-cultivated Mollisol (MO). The results showed that clay content and the specific surface area of soil aggregates decreased, while soil organic carbon, aggregate stability, and surface fragment structure increased for all treatments as compared to those for the PM. Mineral fertilization alone did not increase aggregate stability; however, the combination of mineral and organic fertilization increased aggregate stability by 117%. Compared to the PM, the treated soils showed an increase in porosity as determined by synchrotron radiation X-ray micro-computed tomography (SR-µCT). Compared to naturally restored grasslands, the soil under crop rotation with tillage showed a decrease in pore roundness by 15%; however, supplementation with a large amount of organic input during cultivation increased pore roundness. The principal component analysis using all the indicators showed that the soil structure after 8-year cultivation was not comparable to that of the well-developed MO. Our results revealed the development of PM structure under various agricultural practices and highlighted the co-interaction effects of mineral fertilizers and organic inputs on the properties of soil aggregates during the early stage of pedogenesis.

A new method for disentangling the coupling effect of slaking and mechanical breakdown on aggregate stability: Validation on splash erosion

Aggregate breakdown strongly influences soil erosion process, during which slaking and mechanical breakdown are two dominant breakdown mechanisms. Despite of many methods on aggregate stability, there is a paucity of satisfactory one to disentangle how these two mechanisms interact in aggregate breakdown. Herein, on the basis of Le Bissonnais method (1996) including three treatments (i.e., fast wetting (FW), stirring after pre-wetting (WS), and slow wetting (SW)), a new treatment of water-stirring after fast wetting (SF) was proposed in order to evaluate the coupling effect of slaking and mechanical breakdown on aggregate stability. The coupling effect of slaking and mechanical breakdown was larger to a varying extent than their individual effects, and its difference with slaking showed a unimodal variation with increased aggregate stability. This new method can partition the unique and shared effects of these two breakdown mechanisms; the shared effect (0–77%) decreased logarithmically with increased aggregate stability; the unique effect of slaking (16–52%) showed a unimodal variation and much larger than that of mechanical breakdown (0–17%). As validated by previously published splash erosion data over a wide range of soils (including various soil types, land uses, textures and parent materials), the proposed aggregate stability indices in this new method showed better performance in predicting splash erosion compared to existing ones (e.g., RSI×RMI and RSI/RMI). Collectively, this new method facilitates a systematic understanding on aggregate breakdown mechanisms and exhibits great superiority in aggregate stability measurement and erosion prediction.

Long-term plastic film mulching altered soil physicochemical properties and microbial community composition in Shiyang River Basin, Northwest China

Plastic film mulching (PM) is used widely to improve crop water productivity in the arid regions of Northwest China. However, there are increasing concerns about the potential harm to soil health due to the presence of residue plastic film (RPF) mixed into the soil after long-term field mulching. In our study, we investigated the density of RPF in farmland topsoil (0 to 40 cm) (Exp. I) by analyzing 75 soil samples collected from 15 fields with varying durations of PM (ranging from 3 to 27 years). In addition, we examined the impact of long-term PM and PM + BM (BM, biodegradable film mulching) on soil health (Exp. II) based on an 8-year field experiment. The results illustrated that the weight of RPF ranged from 42.7 to 165.9 kg ha−1 after 3 to 27 years of mulching, with 10 out of 15 fields exceeded the national standard of China (75 kg ha−1). Compared with no film mulching treatment (NM), the long-term PM treatment significantly increased aggregate stability, while significantly decreased soil pH and the enzymatic activities of sucrase by 1.5 % and 33.4 %, respectively. Further, the Chao1, Shannon and Pielou's indices of bacteria significantly decreased after 8 years of PM. Compared with PM and NM, PM + BM treatment significantly improved the Chao1, Shannon and Pielou's indices of bacteria and altered the relative abundance of dominant bacterial and fungal phyla. The principal coordinates analysis (PCoA) revealed significant changes in the soil bacterial and fungal community structure under PM + BM, with the soil fungal community displaying higher sensitivity to PM + BM compared to PM. No significant differences were observed in soil organic matter (SOM), soil microbial biomass C (MBC), soil microbial biomass N (MBN) contents and the enzymatic activities of soils between PM + BM and PM treatments. Overall, BM could be a promising alternative to polyethylene plastic film for improving soil health and is recommended for farming practice in the arid regions of Northwest China.

Legume-based crop diversification reinforces soil health and carbon storage driven by microbial biomass and aggregates

Diversified cropping is a crucial management practice for increasing carbon (C) and nitrogen (N) sequestration in agroecosystems. However, knowledge gaps regarding the mechanisms by which diversified cropping affects C sequestration and soil quality remain unclear. Herein, a field experiment across six-year was performed to explore the effect of three contrasting cropping systems (i.e., winter wheat/summer maize, winter wheat/summer maize-early soybean, and nature fallow) on soil quality and C sequestration, as well as their main drivers at both 0–20 cm and 20–40 cm soil depths. Diversified cropping increased soil organic C (SOC) stock by 9% and the majority of the soil biochemical metrics in the topsoil despite a 40% reduction in the fertilizer application relative to wheat/maize. This was attributed to increased SOC content in large macroaggregates and enhanced microbial turnover due to diverse fresh residue inputs under diversified cropping. Alternatively, the soil organic C, microbial biomass C, C-acquisition enzyme activity, and N-acquisition enzyme activity in large macroaggregates (> 2 mm) were increased by 15%, 15%, 32%, and 16% in the topsoil under diversified cropping versus wheat/maize, respectively. Partial least squares path model displayed that increased C sequestration was mainly driven by microbial biomass C irrespective of the bulk- and aggregate scale. Furthermore, diversified cropping increased the soil quality index by 1- to 2-fold relative to maize/wheat since increased aggregate stability benefited soil structure and nutrient cycling regardless of soil depth. Overall, increased SOC stock is dominantly driven by microbial biomass C, and the improved soil quality is mainly impelled by soil organic C and aggregate stability in responding to diversified cropping were expected to create win-win scenarios for agroecosystems.

Remediation and mitigation measures to counteract orchard soil degradation by treated wastewater irrigation

Recent studies have shown that long-term irrigation with treated wastewater (TWW11Treated wastewater irrigation (TWW): Freshwater (FW): Blended TWW:FW in a 1:1 ratio (MIX): Low-frequency TWW-irrigation (LFI): TWW irrigated tuff trenches (TUF)) can lead to land degradation and reduction of crop performance in clayey soils due to additions of salts and organic compounds. This study investigated the effects of two remediation and two mitigation methods intended to alleviate the damage to soil properties following long-term irrigation with TWW. The experiment was conducted in a ‘Hass’ avocado orchard (Persea americana Mill.) grown on a clayey soil irrigated with TWW since 2009. The treatments implemented in 2016 included: TWW (control), freshwater (FW), blended TWW:FW in a 1:1 ratio (MIX), low-frequency TWW-irrigation (LFI), and TWW irrigated tuff trenches (TUF). The results showed that FW and MIX significantly reduced total salinity, salinity-related ions (Na and Cl), and sodium adsorption ratio (SAR) to (i) depths of 90 cm and 30 cm under drippers, respectively, and (ii) depths of 60 cm (except for chloride) and 30 cm between drippers, respectively, compared with TWW. TUF and LFI reduced soil salinity and sodicity under drippers but not between drippers compared with TWW. Moreover, FW significantly increased aggregate stability to a depth of 30 cm. TUF had the highest oxygen concentration in the root zone (35 cm depth), followed by FW. Considering the scarcity of freshwater, MIX and TUF are suggested as possible measures for reducing soil salinity and sodicity, and increasing aeration of clayey soils under long-term irrigation with TWW, respectively. Our findings contribute valuable insights into strategies for remediating and mitigating the detrimental effects of TWW irrigation on soil, thus promoting sustainable agriculture in regions facing water scarcity.

Impact of agronomic practices on physical surface crusts and some soil technical attributes of two winter wheat fields in southern Iraq

PurposeAgricultural management as tillage systems and manure application can contribute effectively to controlling physical surface crusts (SCs), improving the soil’s technical characteristics and germination rates. While agronomic practices are generally applied to winter wheat fields in southern Iraq, no previous study has explored their impact in combination with SCs and soil physical attributes on wheat productivity (WP) under different soil textures.Materials and methodsThe impact of different agronomic management practices on the formation of soil physical surface crusts (SCs), soil compaction (measured by soil penetration resistance, SPR), soil volumetric water content (VWC), soil bulk density (ρb), mean weight diameter of aggregates (MWD), and WP was examined in two soil textures (clay loam, clay) during 2020 and 2022.Experimental data were subjected to an identical and randomized complete block design (RCBD) under a nested-factorial experimental design, where nine treatments with three replicates each were selected. This included three tillage practices (conventional tillage system (CT), till-plant (TP), and rotational tillage (NTCT)), alongside a sub-treatment with organic fertilizers (cattle manure (CF), and wheat straw (WR)), or without added fertilizer (WT).Results and discussionResults showed that CT treatment increased SCs during wheat growth stages by significantly increasing aggregate stability. A significant difference in ρb and SPR and a higher distribution of VWC were seen under CT treatment when compared to TP and NTCT treatments. TP treatment showed a significantly increased in SPR and ρb, particularly in clay loam. The MWD under TP and NTCT was significantly different to CT treatment, which may be explained by an increase in soil stability due to their management practices. Additionally, both organic fertilizers (CF and WR) significantly enhanced SCs, SPR, VWC, ρb, MWD, and WP.ConclusionsThese data showed a strong relationship between SCs and ρb and between VWC and SPR, which are directly affected by the soil’s water content.

Seasonal variation of the rhizosphere soil aggregation in an Oxisol

Soil aggregation is a key process that results in soil structure formation and stabilization and controls several soil functions. The root system and its mycorrhiza symbiosis contribution to aggregate stabilization have been widely studied. However, only a few studies have considered a large variety of cropping systems under different seasons within tropical environments. Our goal was to better understand the response of aggregate stability in the rhizosphere (RS) and bulk soil (BS) to six cropping systems in an Oxisol, in the summer and winter seasons. Readily-dispersible clay and mechanically-dispersible clay were evaluated as aggregate stability indicators. RS and BS were also characterized for soil physical (i.e., water content), chemical (i.e., soil organic carbon, K, P, Ca, Mg, Al, potential acidity), and physicochemical (i.e., pH, ΔpH, and point of zero charge) properties. Dispersible clay was approximately 1.2 times lower (p < 0.05) within the RS than in the BS, which suggests that the crop root systems increased aggregate stability, but their influence on soil aggregation differed among cropping systems. Aggregate stability was approximately 3 times higher (p < 0.05) in the winter compared to the summer season. In general, RS had better chemical and physicochemical soil parameters than BS. Winter season also showed better chemical and physicochemical parameter values. Overall, these results reflect (i) the positive root system influence of the winter crops on soil structure stability, (ii) the negative response of soil structure stability to the addition of high doses of chemical fertilizers to soybean and maize (cash crops) in the summer season, (iii) the minimal influence of soybean and maize root system on formation and stabilization of the aggregates in the summer season, and (iv) the different weather condition in the summer and winter seasons. Thus, better erosion control practices and crops that promote soil aggregation should be adopted in the summer season. Finally, attention should also be given to the root exudates and their relationship with soil, as they can either increase or decrease soil aggregation.

Long term influence of alternative corn cropping practices and corn-hay rotations on soil health, yields and forage quality

Modifications to continuous corn production systems can reduce environmental impacts and soil degradation, yet the social viability of these modifications is linked to the degree to which they also influence yields and crop quality. In this study, we focus on forage production systems and evaluate how yields, crop quality, soil health indicators, and associated ecosystem services are influenced by corn-hay rotation treatments, cover cropping, and tillage reduction in silage production using a unique 10-year dataset from Borderview Research Farm in Vermont, United States. Physical, chemical, and biological soil health indicators were monitored annually alongside yields and crop quality in a randomized complete block design experiment. We use a mixed model analysis of variance approach to demonstrate significant influences of time and treatments on yields, crop quality and soil health parameters (at p &amp;lt; 0.05). The winter rye cover crop treatment had no significant influence in this study. No-till significantly increased aggregate stability and had no significant effect on other metrics. When cover crop and no-till were combined, they significantly increased soil organic matter content, respiration and aggregate stability. The cover crop, no-till, and no-till cover crop combination treatments had no significant effect on yields or forage quality, suggesting these conservation practices can be adopted without sacrificing yields. Our study also found that corn-hay rotations can significantly increase soil organic matter, respiration, aggregate stability, and crude protein content compared to continuous corn, but they can negatively influence active carbon, total dry matter yield and digestibility. The length of rotation influences the degree to which corn-hay rotations maintain or reduce yields when compared to continuous corn. Shorter rotations of perennial forages (4 years of hay, 6 years of corn) can sustain dry matter yields that are not significantly different from continuous corn, but longer perennial forage rotations (8 years of hay, 2 years of corn) will significantly reduce overall dry matter yields. Among the treatments, no-till in combination with cover cropping in corn silage fields, and a rotation of 4 years of hay to 6 years of corn are likely to achieve the greatest overall benefits in forage production systems.

The effects of forage grasses and legumes on subsequent potato yield, nitrogen cycling, and soil properties

To balance economic potato production with environmental risks, it is crucial to understand the effects of forage crops preceding potatoes on soil nitrate (NO 3 - ) leaching potential, soil quality and potato yield. This study compared a legume forage (red clover, RC), a grass forage (timothy, T), and a red clover-timothy mixture (M) over two cycles of a 3-yr rotation (barley underseeded with forage-forage-potato) from 2013 to 2018. The forage crops were grown under low input maintenance system receiving only starter N fertilizer during the establishment year. Legume-based forages (i.e., RC and M) had greater dry matter accumulation and lower C:N ratio, and therefore added a greater quantity and quality of organic matter inputs to the soil compared with the grass-based forage (T). This resulted in increased soil N supply to the subsequent potato crop, and improved soil quality as indicated by increased aggregate stability, permanganate oxidizable carbon (POX-C), autoclaved citrate extractable soil protein (ACE), and flush of CO 2 upon rewetting a dried soil for legume- than grass-based forages. Under N limited conditions (i.e., no N fertilizer applied) forage legumes were associated with higher potato yield than forage grass. However, tuber yield was not increased when N fertilizer was applied, a finding attributed to a better synchrony between potato N uptake and soil N supply in the presence of N fertilizer with the forage grass treatment. The legume-based forages improved soil quality, increased soil N supply as well as NO 3 - leaching losses. Results of this study suggest that there may be a trade-off between selecting forage crops to reduce NO 3 - leaching and to enhance soil quality. • Compared forage legumes and grasses on soil quality, N cycling, and potato yield. • Soil quality improved, soil N supply and nitrate leaching increased with legumes. • Higher potato yield with legumes than grasses only under N limiting conditions. • Trends towards higher potato yield with forage grasses with N fertilizer applied. • Trade-offs between improving soil quality and potato yield and reducing N leaching.

Compost amendment to enhance carbon sequestration in rangelands

Rangelands contain 20% of global soil carbon (C). Past management of rangelands has resulted in significant losses of soil C, threatening the long-term productivity and sustainability of these ecosystems. Compost amendments have been proposed as a means to increase soil C sequestration while providing important cobenefits to rangeland ecosystems and land managers. Here, we review the literature on the effects of compost amendments on soil and plant characteristics and rates of soil C storage. We extracted values related to biological, physical, and chemical responses to compost applications in rangelands in eight countries and on five continents. Studies reported both short (&lt;1 y) and long-term (&gt;12 y) effects with compost types derived from green waste, food waste, manure, and biosolids. Generally, we found that compost amendments improved aboveground production by &gt;40%, and belowground C content by 50%. Further benefits of compost additions included increasing aggregate stability (~42%), water retention (~18%), nutrient availability (~37% and 126% for nitrogen [N] and phosphorus [P], respectively), as well as generally reducing erosion but with high variability. We found little to no effect of compost amendments on plant diversity and very few studies investigated effects on soil microbial community and function. Both field and modeling studies demonstrated that the changes in soil C from compost amendments can result in long-term C storage. Overall, results suggest that compost amendments may contribute to rangeland resilience to climate change with the additional benefit of climate mitigation via soil C sequestration.

Assessment of beneficial fungal microorganism’s bio-efficacy in stimulating morphological and physiological parameters of Allium cepa plants grown in soil amended with fish wastes

BackgroundThe increase in the human consumption of fish results in the production of organic fish wastes (FW). For enhanced soil fertility and plant growth at a lower cost and without the negative impacts of chemical fertilizers, these wastes could be employed as a valuable organic fertilizer. To determine the synergistic bio-efficacy of Trichoderma sp. and arbuscular mycorrhizal (AM) fungi in stimulating the morphological and physiological characteristics of FW-fertilized Alium cepa, as well as to investigate their involvement in boosting soil fertility, the current study was carried out. Overall, eight treatments were applied as follows: AM, Trichoderma sp., AM + Trichoderma sp., FW, AM + FW, Trichoderma sp. + FW, AM + Trichoderma sp. + FW, and control. Growth and physiological assessments of onion plants were taken after 8 weeks from FW application.ResultsOur results showed that FW application combined with AM fungi and Trichoderma sp. inoculations increased aggregate stability of the soil (glomalin content) and soil chitinase activity. Moreover, using the bio-inoculations along with FW amendments significantly (p < 0.05) improved the photosynthetic pigments, protein, carbohydrates, and nutrients content of onion plants. It's interesting to note that the triple interaction of AM + Trichoderma sp. + FW led to the greatest increase in plant height, root length, number of leaves, and leaf area as well as total fresh and dry weights of shoots and roots. Besides, AM fungal colonization was at its highest percentage with Trichoderma sp. inoculation, although this percentage decreased with FW addition.ConclusionWe concluded that the combined treatments of AM fungi and Trichoderma sp. along with FW application to the soil can be proposed as a successful strategy for plant performance in nutrient-deficient soils as both fungal inoculants are capable of degrading these wastes and converting them into manure suitable for farming so plants can uptake the minerals effortlessly.

Site characteristics determine the duration of structure liming effects on clay soil

Adding carbonated or non-carbonated lime to clay soils can lead to changes in aggregate stability. In Sweden, ‘structure liming’ with a mixed product (normally 80–85% calcium carbonate and 15–20% calcium hydroxide) is subsidised through environmental schemes to increase aggregate stability, thereby mitigating losses of particulate phosphorus (PP). This study assessed the effects of structure liming on aggregate stability in eight clay soils in southern Sweden, using turbidity as a proxy for aggregate stability. Turbidity in leachate from simulated rain events performed on aggregates (2–5 mm) in the laboratory was measured one and six years after application of four treatments 0, 4, 8 and 16 t ha-1 of a mixed structure liming product. The effect on turbidity was analysed for all application rates, but also as the contrast between the unlimed control and the mean of the limed treatments, to identify the general effect. A significant effect of structure liming on turbidity was found after one year. The effect decreased over time, but was still detectable after six years. However, there was a significant interaction between trial and treatment, indicating different reactions on different soils and suggesting that not all clay soils are suitable for structure liming if the desired objective is to lower the risk of PP losses. Clay content, initial pH and mineralogy may explain the different responses to structure liming. These findings show a need for a site-specific structure liming strategy. As a tentative recommendation, soils with a minimum clay content of approximately 25–30% and pH &lt;7 should be preferred for structure liming.

Evaluation of aggregate stability methods for soil health

Aggregate stability is a commonly used indicator of soil health because improvements in aggregate stability are related to reduced erodibility and improved soil–water dynamics. During the past 80 to 90 years, numerous methods have been developed to assess aggregate stability. Limited comparisons among the methods have resulted in varied magnitudes of response to soil health management practices and varied influences of inherent soil properties and climate. It is not clear whether selection of a specific method creates any advantage to the investigator. This study assessed four commonly used methods of measuring aggregate stability using data collected as part of the North American Project to Evaluate Soil Health Measurements. The methods included water stable aggregates using the Cornell Rainfall Simulator (WSACASH), wet sieved water stable aggregates (WSAARS), slaking captured and adapted from SLAKES smart-phone image recognition software (STAB10), andthemean weight diameter of water stable aggregates (MWD).Influence of climate and inherent soil properties at the continental scale were analyzed in addition to method responses to rotation diversity, cash crop count, residue management, organic nutrient amendments, cover crops, and tillage. The four methods were moderately correlated with each other. All methods were sensitive to differences in climate and inherent soil properties between sites, although to different degrees. None measured significant effects from rotation diversity or crop count, but all methods detected significant increases in aggregate stability resulting from reduced tillage. Significant increases or positive trends were observed for all methods in relation to cover cropping, increased residue retention, and organic amendments, except for STAB10, which expressed a slightly negative response to organic amendments. Considering these results, no single method was clearly superior and all four are viable options for measuring aggregate stability. Therefore, secondary considerations (e.g., cost, method availability, increased sensitivity to a specific management practice, or minimal within-treatment variability) driven by the needs of the investigator, should determine the most suitable method.

Superabsorbent Polyacrylamide Effects on Hydrophysical Soil Properties and Plant Biomass in a Sandy Loam soil

ABSTRACT There is a complicated relationship between land degradation, water efficiency, and crop yield in arid and semiarid regions. In the Semiarid Pampa region, Argentina, land use changes that affected fragile lands (high content of fine sands plus silt and low organic carbon) have decreased soil quality, thus endangering agricultural activities. The use of polyacrylamide (PAM) is an option for increasing productivity and protecting soil resources. However, there is scarce information about superabsorbent PAM on water storage linked to aggregate stability mechanisms in this fragile land. Hydrophysical variables and plant biomass were evaluated in a greenhouse pot experiment. Three factors were analyzed: 1) PAM rates (doses): D0 = 0%, D1 = 0.04%, and D2 = 0.08%; 2) vegetation presence (Festuca arundinacea ssp.): vegetation (+) and vegetation (–) and; 3) water regime: field capacity (FC) and half field capacity (FC/2). After 5 months, the incorporation of superabsorbent PAM had a strong effect on most hydrophysical variables. Storage variables (available water content and easily available water content) were improved mainly by increasing water retention at lower suctions (i.e. large pores). Dose increments regardless of the water regime led to higher plant biomass (P < .05). PAM incorporation enhanced abiotic mechanisms (swelling–shrinkage, cracks formation) and biotic mechanisms (root activity – direct, increment water retention – indirect) acting synergically to increase aggregate stability and water storage. Aggregate stability tests (fast wetting test – FW, slow wetting test – SW, and stirring aggregates after ethanol submersion – Stir) proved to be useful in discriminating stabilization mechanisms of soils, highlighting the effect of PAM incorporation on soil cohesion (Stir). Finally, superabsorbent PAM may contribute to maintain crop yields, leading to soil quality amelioration.

Liming alkaline clay soils: effects on soil structure, nutrients, barley growth and yield

ABSTRACT Liming before cultivation of sugar beets is favourable even on alkaline soils but knowledge of response in other crops is lacking. Therefore, effects of ground limestone (GL) and structure lime (SL1 slaked lime or SL2 mix of ground limestone and slaked lime) were evaluated in southern Sweden on soil structure, growth and nutrient concentration in barley under four fertilisation strategies 1.5–2 years after application. All lime products increased aggregate stability, but with variations between locations. A lower proportion of large aggregates was found in both limed treatments, and a higher proportion of small aggregates in SL. In barley, grain yield was unaffected while shoot numbers and biomass in first node stage increased for GL and biomass increased further for SL. Structure lime increased potassium concentration in plants in first node stage, due to more potassium in the product. Both lime types increased molybdenum concentration. Ground limestone reduced zinc concentration compared with no liming. Finer seedbed tilth and increased aggregate stability may explain increased biomass for GL. Higher potassium content in SL might be a further explanation. No interactions between liming and fertilisation were found. In conclusion, on the soil types studied, no change of fertilisation strategy is needed due to liming.

Role of earthworms in soil fertility and its impact on agriculture: A review

Soil fertility is defined as the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation. Perhaps no other living organism in the soil is as important as an earthworm in helping to increase soil health. Earthworms are the most commonly occur in the soil. The activities of burrowing and feeding by earthworms have many valuable effects generally on soil quality for crop production. Earthworms increase soil aeration, infiltration, structure, nutrient cycling, water movement, and plant growth. Earthworms are one of the major decomposers of organic matter. They get their nutrition from microorganisms that live on organic matter and in soil material. When they move through the soil eating, earthworms form tubular channels or burrows. These burrows can persist for a long time in the soil. Earthworm burrows increase soil porosity which increases the amount of air and water that get into the soil. Increased porosity also lowers bulk density and increases root development. Earthworm excrement or casts increase soil fertility because it contains nitrogen, phosphorus, potassium, and magnesium. Earthworm casts also contain microorganisms which increase in abundance as organic matter is digested in their intestines. The cycling of nutrients from organic matter and the increase in microorganisms facilitates plant growth. They cast along with binding agents released by earthworms also improve soil structure and increase aggregate stability. The soil biota benefits soil productivity and contributes to the sustainable function of all ecosystems. The cycling of nutrients is a critical function that is essential to life on earth. Earthworms (EWs) are a major component of soil fauna communities in most ecosystems and comprise a large proportion of macrofauna biomass. Their activity is beneficial because it can enhance soil nutrient cycling through the rapid incorporation of detritus into mineral soils. In addition to this mixing effect, mucus production associated with water excretion in earthworm guts also enhances the activity of other beneficial soil microorganisms. This is followed by the production of organic matter. So, in the short term, a more significant effect is the concentration of large quantities of nutrients (N, P, K, and Ca) that are easily assimilable by plants in fresh cast depositions. In addition, earthworms seem to accelerate the mineralization as well as the turnover of soil organic matter. Earthworms are known also to increase nitrogen mineralization, through direct and indirect effects on the microbial community. The increased transfer of organic C and N into soil aggregates indicates the potential for earthworms to facilitate soil organic matter stabilization and accumulation in agricultural systems, and that their influence depends greatly on differences in land management practices.

Warming and Labile Substrate Addition Alter Enzyme Activities and Composition of Soil Organic Carbon

Warming can increase the efflux of carbon dioxide (CO2) from soils and can potentially feedback to climate change. In addition to warming, the input of labile carbon can enhance the microbial activity by stimulating the co-metabolism of recalcitrant soil organic matter (SOM). This is particularly true with SOM under invaded ecosystems where elevated CO2and warming may increase the biomass of invasive species resulting in higher addition of labile substrates. We hypothesized that the input of labile carbon would instigate a greater soil organic carbon (SOC) loss with warming compared to the ambient temperature. We investigated this by incubating soils collected from a native pine (Pinus taeda) forest to which labile carbon from the invasive species kudzu (Pueraria lobata) was added. We evaluated the microbial extracellular enzyme activity, molecular composition of SOC and the temperature sensitivity of soil CO2efflux under warming and labile carbon addition. After 14 months of soil incubation, the addition of labile C through kudzu extract increased the activity of β-1,4-glucosidase compared with the control. However, the activity of N-acetyl-β-D-glucosaminidase and fungal biomass (ergosterol) decreased with labile carbon addition. The activity of peroxidase increased with warming after 14 months of soil incubation. Although the carbon content of incubated soils did not vary with substrate and temperature treatments, the molecular composition of SOC indicated a general decrease in biopolymers such as cutin, suberin, long-chain fatty acids, and phytosterol with warming and an increasing trend of microbial-derived compounds with labile substrate addition. In soils that received an addition of labile C, the macro-aggregate stability was higher while the temperature sensitivity of soil C efflux was lower compared with the control. The increase in aggregate stability could enhance the physical protection of SOC from microbial decomposition potentially contributing to the observed pattern of temperature sensitivity. Our results suggest that warming could preferentially accelerate the decomposition of recalcitrant compounds while the addition of labile substrates could enhance microbial-derived compounds that are relatively resistant to further decomposition. Our study further emphasizes that global change factors such as plant invasion and climate change can differentially alter soil microbial activity and the composition of SOC.