Immediate and subsequent effects of drying and rewetting on microbial biomass in a paddy soil

Many surface soils in Japan may experience more frequent and intense drying–rewetting (DRW) events due to future climate changes. Such DRW events negatively and positively affect microbial biomass carbon (MBC) through microbial stress and substrate supply mechanisms, respectively. To assess the MBC immediately after DRW and during the incubation with repeated DRW cycles, two laboratory experiments were conducted for a paddy soil. In the first experiment, we exposed the soil to different drying treatments and examined the MBC and hourly respiration rates immediately after the rewetting to evaluate the microbial stress. In the second experiment, we compared microbial growth rates during the incubation of the partially sterilized soil with a continuously moist condition and repeated DRW cycles to evaluate the contribution of the substrate supply from non-biomass soil organic C on MBC. First, all drying treatments caused a reduction in MBC immediately after the rewetting, and higher drying intensities induced higher reduction rates in MBC. A reduction of more than 20% in MBC induced the C-saturated conditions for surviving microbes because sufficient concentrations of labile substrate C were released from the dead MBC. Second, repeated DRW cycles caused increases in the microbial growth rates because substrate C was supplied from non-biomass organic C. In conclusion, MBC decreased immediately after DRW due to microbial stress, whereas MBC increased during repeated DRW cycles due to substrate C supplied from non-biomass organic C.     

Short-term effects of soil amendment with meadowfoam seed meal on soil microbial composition and function

Meadowfoam (Limnanthes alba Hartw. ex Benth) seed meal (MSM), a by-product of meadowfoam oil extraction, has a secondary metabolite known as glucosinolate glucolimnanthin. MSM applied as a soil amendment has been reported to have herbicidal and fertilizer properties. Experiments were conducted over 28 days to evaluate short-term effects of a MSM application on soil microbial communities. MSM was applied to soil as either a full or a split application. In addition to MSM and untreated control treatments, urea was used as a N source to account for the fertilizer effect of the seed meal. Urea was applied either as a full or a split rate on the same schedule as MSM. Soil microbial activities were not different between the full and the split rate applications of MSM. After day 7 following MSM application, carbon-source utilization of microbial communities of MSM was different from the urea and control treatments. Microbial communities in MSM treatments utilized complex carbon sources to a relatively greater degree than microbial communities in urea or control treatments. The C and N inputs from MSM increased the gross metabolic activity of the mixed microbial population. Basal respiration was stimulated and microbes reallocated carbon input to biomass and enzyme production. Within 7 and 14 days after MSM application, the reallocation occurred quickly and microbial biomass increased by at least 80% for C and 95% for N compared to the untreated control. In the short-term, MSM treatments affected nutrient dynamics, and the soil microbial structure and function. The effects of MSM application on the composition of bacterial and fungal communities warrant additional study.     

Sugarcane by-products used as soil amendments on a sandy soil: Effects on sugarcane crop nutrition and yield

Agricultural by-products applied as soil amendments have the potential to improve crop production on low organic matter (OM) soils. This two-year study investigated the use of two readily available sugarcane (Saccharum spp.) milling by-products, mill mud, and mill ash, as soil amendments to improve first sugarcane crop (plant cane) and subsequent crop (first ratoon) grown on a sandy Spodosol. Sugarcane was grown in lysimeters receiving mill mud, mill ash, and a 50:50 (v:v) mill mud to mill ash mix. Amendments were applied at low, medium, and high application rates (5, 10, and 15 cm depths, respectively) and then incorporated 30 cm deep. Amendment effects on plant nutrition, soil characteristics, and crop yield were determined. High rate applied mill mud and mill ash had the highest soil OM content for both years and soil OM did not significantly change between crops for all treatments except for high rate mill mud, which increased the second year (ratoon crop). Leaf nutrient levels for nitrogen (N), iron (Fe), and copper (Cu) for all treatments both years were insufficient; nutrient levels for magnesium (Mg), manganese (Mn), and silicon (Si) were within marginal to sufficient range for all treatments both years. All amendments produced significantly higher biomass and sucrose yields for plant cane and first ratoon crops compared to the control. Mill ash treatments produced the greatest increase in sucrose and biomass yields from plant cane to ratoon crops, which corresponded with an increase in potassium (K) in leaf tissue. However, mid and high rates of mix produced the highest sugarcane biomass and sucrose yields for the both the plant cane and ratoon crops.     

Assessing long term effects of compost fertilization on soil fertility and nitrogen mineralization rate

Background

Fertilization with organic waste compost can close the nutrient cycles between urban and rural environments. However, its effect on yield and soil fertility must be investigated.

Aim

This study investigated the long-term effect of compost on soil nutrient and potentially toxic elements (PTEs) concentration, nutrient budgets, and nitrogen (N) mineralization and efficiency.

Methods

After 21 years of annual compost application (100/400 kg N ha^–1 year^–1 [100BC/400BC]) alone and combined with mineral fertilization, soil was analyzed for pH, organic carbon (SOC), nutrient (total N and P, N_min, extractable CAL-P, CAL-K, and Mg), and PTE (Cu, Ni, Zn) concentrations. Yields were recorded and nutrient/PTE budgets and apparent net mineralization (ANM, only 2019) were calculated.

Results

N efficiency was the highest in maize and for mineral fertilization. Compost application led to lower N efficiencies, but increased ANM, SOC, pH, and soil N, and surpluses of N, P, and all PTEs. Higher PTE concentrations were only found in 400BC for Cu. Nutrient budgets correlated with soil nutrient concentration. A surplus of 16.1 kg P ha^–1 year^–1 and 19.5 kg K ha^–1 year^–1 resulted in 1 mg kg^–1 increase in CAL-P and CAL-K over 21 years.

Conclusion

Compost application supplies nutrients to crops with a minor risk of soil-accumulation of PTEs. However, the nutrient stoichiometry provided by compost does not match crop offtakes causing imbalances. Synchronization of compost N mineralization and plant N demand does not match and limits the yield effect. In winter wheat only 65–70% of N mineralization occurred during the growth period.     

硝化抑制剂和秸秆对潮棕壤碳氮转化和微生物群落特征的短期影响

氮是植物和微生物生长繁殖的必需营养元素,而氮矿化表征了土壤供氮能力。通过盆栽实验,采用同位素稀释法和磷脂脂肪酸(PLFA)法,研究了添加硝化抑制剂和秸秆条件下,潮棕壤碳氮矿化和微生物群落组成变化特征。结果表明,与施氮量N 0.1 g·kg~(-1)的单施氮肥处理(NF)相比,氮肥配施1%硝化抑制剂(NFI)的土壤铵态氮提高32%,而硝态氮降低53%。氮肥与施用量为5 g·kg~(-1)的秸秆配施(NS),土壤氮素总矿化速率增加36%,微生物生物量碳提高51%,β-葡萄糖苷酶活性提高36%,同时显著增加了土壤总PLFA以及细菌、真菌、真菌/细菌和革兰式阴性菌(P0.05),土壤呼吸熵降低50%。与氮肥配施秸秆处理(NS)相比,氮肥、秸秆和硝化抑制剂配施处理(NSI),土壤铵态氮提高33%,硝态氮下降47%。综上所述,氮肥和秸秆配施可以提高土壤微生物生物量,改变土壤微生物群落组成,配施1%(N)硝化抑制剂后降低土壤硝化速率,增加土壤供氮能力。     

Effects of soil frost on growth, composition and respiration of the soil microbial decomposer community

Most climate change scenarios predict that the variability of weather conditions will increase in coming decades. Hence, the frequency and intensity of freeze-thaw cycles in high-latitude regions are likely to increase, with concomitant effect on soil carbon biogeochemistry and associated microbial processes. To address this issue we sampled riparian soil from a Swedish boreal forest and applied treatments with variations in four factors related to soil freezing (temperature, treatment duration, soil water content and frequency of freeze-thaw cycles), at three levels in a laboratory experiment, using a Central Composite Face-centred (CCF) experimental design. We then measured bacterial (leucine incorporation) and fungal (acetate in ergosterol incorporation) growth, basal respiration, soil microbial phospholipid fatty acid (PLFA) composition, and concentration of dissolved organic carbon (DOC). Fungal growth was higher in soil exposed to freeze-thawing perturbations and freezing temperatures of −6 °C and −12 °C, than under more constant conditions (steady 0 °C). The opposite pattern was found for bacteria, resulting in an increasing fungal-to-bacterial growth ratio following more intensive winter conditions. Soil respiration increased with water content, decreased with treatment duration and appeared to mainly be driven by treatment-induced changes in the DOC concentration. There was a clear shift in the PLFA composition at 0 °C, compared with the two lower temperatures, with PLFA markers associated with fungi as well as a number of unsaturated PLFAs being relatively more common at 0 °C. Shifts in the PLFA pattern were consistent with those expected for phenotypic plasticity of the cell membrane to low temperatures. There were small declines in PLFA concentrations after freeze-thawing and with longer durations. However, the number of freeze-thaw events had no effect on the microbiological variables. The findings suggest that the higher frequency of freeze-thaw events predicted to follow the global warming will likely have a limited impact on soil microorganisms.     

模拟增温和降水调控对土壤微生物碳氮、群落基质利用模式及群落组成的短期影响

Soil microorganisms are major drivers of soil carbon(C) cycling;however,the response of these microorganisms to climate change remains unclear.In the present study,we investigated how 18 months of multifactor climate treatments(warmed air temperature by 3℃ and decreased or increased precipitation manipulation by 30%) affected soil microbial biomass C and nitrogen(N),community substrate utilization patterns,and community composition.Decreased and increased precipitation significantly reduced microbial biomass C by 13.5% and 24.9% and microbial biomass N by 22.9% and 17.6% in unwarmed plots,respectively(P0.01).Warming enhanced community substrate utilization by 89.8%,20.4%,and 141.4% in the natural,decreased,and increased precipitation plots,respectively.Particularly,warming significantly enhanced the utilization of amine and carboxylic acid substrates among all precipitation manipulation plots.Compared with the natural air temperature with natural precipitation treatment,other treatments affected fungal community richness by -0.9% to 33.6% and reduced the relative abundance of the dominant bacterial and fungal groups by 0.5% to 6.8% and 4.3% to 10.7%,respectively.The warming and/or precipitation manipulation treatments significantly altered Zygomycota abundance(P0.05).Our results indicate that climate change drivers and their interactions may cause changes in soil microbial biomass C and N,community substrate utilization patterns,and community composition,particularly for the fungal community,and shifts in the microorganism community may further shape the ecosystems function.     

Mechanisms of real and apparent priming effects and their dependence on soil microbial biomass and community structure: critical review

The number of studies on priming effects (PE) in soil has strongly increased during the last years. The information regarding real versus apparent PE as well as their mechanisms remains controversial. Based on a meta-analysis of studies published since 1980, we evaluated the intensity, direction, and the reality of PE in dependence on the amount and quality of added primers, the microbial biomass and community structure, enzyme activities, soil pH, and aggregate size. The meta-analysis allowed revealing quantitative relationships between the amounts of added substrates as related to microbial biomass C and induced PE. Additions of easily available organic C up to 15% of microbial biomass C induce a linear increase of extra CO₂. When the added amount of easily available organic C is higher than 50% of the microbial biomass C, an exponential decrease of the PE or even a switch to negative values is often observed. A new approach based on the assessment of changes in the production of extracellular enzymes is suggested to distinguish real and apparent PE. To distinguish real and apparent PE, we discuss approaches based on the C budget. The importance of fungi for long-term changes of SOM decomposition is underlined. Priming effects can be linked with microbial community structure only considering changes in functional diversity. We conclude that the PE involves not only one mechanism but a succession of processes partly connected with succession of microbial community and functions. An overview of the dynamics and intensity of these processes as related to microbial biomass changes and C and N availability is presented.     

Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE—Bavaria,Germany

The decrease in anthropogenic deposition, namely SO₄^2— and SO₂, in European forest ecosystems during the last 20 years has raised questions concerning the recovery of forest ecosystems. The aim of this study was to evaluate if the long term data of element concentrations at the Fichtelgebirge (NE‐Bavaria, Germany) monitoring site indicates a relationship between the nutrient content of needles and the state of soil solution acidity. The soil at the site is very acidic and has relatively small pools of exchangeable Ca and Mg. The trees show medium to severe nutrient deficiency symptoms such as needle loss and needle yellowing. The Ca and Mg concentrations in throughfall decreased significantly during the last 12 years parallel to the significant decline in the throughfall of H⁺ and SO₄^2— concentrations. Soil solution concentrations of SO₄^2—, Ca and Mg generally decreased while the pH value remained stable. Aluminum concentrations decreased slightly, but only at a depth of 90 cm. Simultaneously a decrease in the molar Ca/Al and Mg/Al ratios in the soil solution was observed. Ca and Mg contents in the spruce needles decreased, emphasizing the relevance of soil solution changes for tree nutrition. The reasons for the delay in ecosystem recovery are due to a combination of the following two factors: (1) the continued high concentrations of NO₃^— and SO₄^2— in the soil solution leading to high Al concentrations and low pH values and, (2) the decreased rates of Ca and Mg deposition cause a correlated decrease in the concentration of Ca and Mg in the soil solution, since little Ca and Mg is present in the soil's exchangeable cation pools. It is our conclusion that detrimental soil conditions with respect to Mg and Ca nutrition as well as to Al stress are not easily reversed by the decreasing deposition of H⁺ and SO₄^2—. Thus, forest management is still confronted with the necessity of frequent liming to counteract the nutrient depletion in soils and subsequent nutrient deficiencies in trees.     

High soil Mn and Al,as well as low leaf P concentration,may explain for low natural rubber productivity on a tropical acid soil in Vietnam

The aim of the current study was to identify major soil and leaf factors accounting for low natural rubber (NR, Hevea brasiliensis) productivity on tropical acid Acrisols in Vietnam. Twenty NR plots were measured with NR productivity, leaf factors (N, P, K, Ca, Mg, Mn, Cu, Fe, and Zn), soil factors (pH, particle size distribution, total C, N, P, K, exchangeable K, Ca, Mg, Al, Mn, Fe, Zn, available P). Cluster analysis showed that NR productivity could be separated into three clusters with low (23.2), medium (38.2), and high (61.3 g tree^?1 harvest^?1) yield. High-yield cluster had higher leaf P concentration and soil pH, while low-yield cluster had higher leaf Mn, soil exchangeable Al, and Mn concentration. Simple and multiple linear regression analysis applied with backward elimination procedure suggested that leaf and soil toxic concentration may be responsible for low NR productivity in the study soil.     

Recent advances in the chemistry of nitrogen,phosphorus and potassium as fertilizers in soil: A review

The advent of civilization has made humans dependent on plants for food and medicine, leading to the intensification of agricultural production. The intense cultivation of crops has resulted in the depletion of available nutrients from soil, thereby demanding the application of excess nutrients to soil to improve yield. Thus, mineral fertilizer discovery and application have, in many ways, contributed greatly to meeting global food demands. However, aside from the positive effects of mineral fer...     

Suitability of inorganic and organic amendments for in situ immobilization of Cd,Cu, and Zn in a strongly contaminated Kastanozem of the Mashavera valley,SE Georgia. I. Effect of amendments on metal mobility and microbial activity in soil

The aim was to find an adequate, cost‐efficient in situ remediation technique for the Mashavera valley, a mining area in SE Georgia heavily contaminated with Cd, Cu, and Zn. A 12‐month experiment was conducted to test: iron grit, natural zeolite, biochar, and Divergan® (a scavenger) for soil melioration. The amendments were added in different concentrations to the topsoil of a Kastanozem. Mobile metal concentrations decreased with increasing concentrations of amendments in the sequence Divergan® >> iron grit ≈ natural zeolite > biochar. In the same order amendments enhanced activities of soil microbial respiration, alkaline phosphatase, and dehydrogenase; microbial C also followed this trend. A sequential extraction confirmed a shift from easily mobilized to heavily bound fractions. The addition of 2% (w/w) of Divergan® was sufficient to lower mobile trace metal concentrations below German thresholds by chemisorption, and soil microbial activity was significantly increased. The effects of all other treatments were at a much lower level and not found suitable due to needed application rates.     

Land-use intensification and agroforestry in the Kenyan highland: Impacts on soil microbial community composition and functional capacity

This study investigates microbial communities in soil from sites under different land use in Kenya. We sampled natural forest, forest plantations, agricultural fields of agroforestry farms, agricultural fields with traditional farming and eroded soil on the slopes of Mount Elgon, Kenya. We hypothesised that microbial decomposition capacity, biomass and diversity (1) decreases with intensified cultivation; and (2) can be restored by soil and land management in agroforestry. Functional capacity of soil microbial communities was estimated by degradation of 31 substrates on Biolog EcoPlates™. Microbial community composition and biomass were characterised by phospholipid fatty acid (PLFA) and microbial C and N analyses. All 31 substrates were metabolised in all studied soil types, i.e. functional diversity did not differ. However, both the substrate utilisation rates and the microbial biomass decreased with intensification of land use, and the biomass was positively correlated with organic matter content. Multivariate analysis of PLFA and Biolog EcoPlate™ data showed clear differences between land uses, also indicated by different relative abundance of PLFA markers for certain microorganism groups. In conclusion, our results show that vegetation and land use control the substrate utilisation capacity and microbial community composition and that functional capacity of depleted soils can be restored by active soil management, e.g. forest plantation. However, although 20–30 years of agroforestry farming practises did result in improved soil microbiological and chemical conditions of agricultural soil as compared to traditional agricultural fields, the change was not statistically significant.     

Long term tillage,cover crop,and fertilization effects on microbial community structure,activity: Implications for soil quality

Conservation agriculture practices, such as reduced tillage, cover crops and fertilization, are often associated with greater microbial biomass and activity that are linked to improvements in soil quality. This study characterized the impact of long term (31 years) tillage (till and no-till), cover crops (Hairy vetch- Vicia villosa and winter wheat- Triticum aestivum, and a no cover control), and N-rates (0, 34, 67 and 101 kg N ha⁻¹) on soil microbial community structure, activity and resultant soil quality calculated using the soil management assessment framework (SMAF) scoring index under continuous cotton (Gossypium hirsutum) production on a Lexington silt loam in West Tennessee.No-till treatments were characterized by a significantly greater (P < 0.05) abundance of Gram positive bacteria, actinomycetes and mycorrhizae fungi fatty acid methyl ester (FAME) biomarkers compared to till. Saprophytic fungal FAME biomarkers were significantly less abundant (P < 0.05) under no-till treatments resulting in a lower fungi to bacteria (F:B) ratio. Key enzymes associated with C, N & P cycling (β-glucosidase, β-glucosaminidase, and phosphodiesterase) had significantly higher rates under no-till relative to till, corresponding to significantly greater (P < 0.05) soil C and N, extractable nutrients (P, K and Ca) and yields. Mycorrhizae fungi biomarkers significantly decreased (P < 0.05) with increasing N-rate and was significantly less (P < 0.05) under the vetch cover crop compared to wheat and no cover. Treatments under vetch also had significantly higher β-glucosaminidase and basal microbial respiration rates compared to wheat and no cover.Consequently, the total organic carbon (TOC) and β-glucosidase SMAF quality scores were significantly greater under no-till compared to till and under the vetch compared to wheat and no cover treatments, resulting in a significantly greater overall soil quality index (SQI).Our results demonstrate that long-term no-till and use of cover crops under a low biomass monoculture crop production system like cotton results in significant shifts in the microbial community structure, activity, and conditions that favor C, N and P cycling compared to those under conventional tillage practices. These practices also led to increased yields and improved soil quality with no-till having 13% greater yields than till and treatments under vetch having 5% increase in soil quality compared to no cover and wheat.     

Effects of Lumbricus terrestris, Allolobophora chlorotica and Eisenia fetida on microbial community dynamics in oil-contaminated soil

Oil spills are one of the most common types of soil pollution. Bioremediation has become an attractive alternative to physicochemical methods of remediation, where feasible. Earthworms have been shown to stimulate the degradation of petroleum hydrocarbons in soil, and it was hypothesized that the role of earthworms in remediation lies in the enhancement of an oil degrading microbial community. The aim of this study was to characterize microbial activity and community dynamics in oil-contaminated soil incubated with or without earthworms. Three earthworm species (Eisenia fetida, Allolobophora chlorotica and Lumbricus terrestris) were incubated in crude oil polluted soil (ca. 10,000 mg/kg total petroleum hydrocarbons (TPH)) and a reference soil for 28 d. Control treatments with manual mixing and/or cattle dung amendment were also included. In the oil-contaminated soil, respiration and concentration of microbial biomass was significantly enhanced by earthworm amendment, and TPH concentrations decreased significantly. These effects were less evident in treatments with A. chlorotica, possibly due to a difference in behavior, since individuals of this endogeic species were found in a state of inactivity (aestivation). Microbial community dynamics were described by phospholipid fatty acid (PLFA) analyses. After 28 d, similar shifts in the soil PLFA composition were observed in the oil-contaminated soil irrespective of worm species. Fungal:bacterial ratios were increased in the presence of worms, but also by addition of dung as a food source, indicating a non-specific effect of metabolizable substrates. In contrast, the fatty acids 17:1ω8 (=Δ9-heptadecenoic acid) and 20:4ω6c (arachidonic acid) were specifically stimulated by the presence of earthworms in the oil-contaminated soil. The results showed that earthworms can contribute positively to bioremediation of oil-contaminated soil, but that the effect may be species-dependent.     

季节性放牧和全年放牧对亚高山草地生态系统中土壤动物和微生物的影响

Grazing and over-grazing may drive changes in the diversity and functioning of below-ground meadow ecosystems.A field soil survey was conducted to compare microbial biomass carbon (Cmin) and soil fauna communities in the two main grassland management systems in subalpine regions of Yunnan Province,China:perennial grazing currently practiced due to increasing herd sizes and traditional seasonal grazing.A three-year exclosure experiment was then conducted to further compare the effects of different grazing practices,including treatments of no mowing,perennial grazing (NM + G),mowing followed by seasonal grazing (M + G),mowing and no grazing (M + NG),and no mowing or grazing (NM + NG).The comparative survey result revealed that Cmin and total density of soil fauna were significantly lower at a perennially grazed site than at a seasonally grazed site.The experiment results showed that in comparison to non-grazing treatments (M + NG and NM + NG),grazing (NM + G and M + G) reduced total fauna density (by 150 individuals m-2) and the number of taxonomic groups present (by 0.32 taxa m-2).Mowing decreased Cmin (by 0.31 mg g-1).Furthermore,the NM + G treatment (perennial grazing) had the lowest density of Collembola (16.24 individuals m-2),one of the two most common taxonomic groups,although other taxonomic groups responded differently to the treatments.Treatment effects on soil fauna were consistent with those on above-ground grasses,in which C:N ratios were greatly reduced by grazing,with this effect being the greatest for the NM + G treatment.In contrast,different grazing treatments had little effect on C:N ratio of soil.Furthermore,the traditional grazing method (mowing followed by seasonal grazing) may have less severe effects on some taxonomic groups than perennial grazing.Therefore,an appropriate management should aim to protect soil fauna and microbes in this area from over-grazing and against further degradation.     

Salt effects on the soil microbial decomposer community and their role in organic carbon cycling: A review

Salinization of soil is recognised as one of the most pressing environmental challenges to resolve for the next century. We here conduct a synoptic review of the available research on how salt affects decomposer microbial communities and carbon (C) cycling in soil. After summarizing known physiological responses of microorganisms to salinity, we provide a brief overview and qualification of a selection of widely applied methods to assess microorganisms in soil to date. The dominant approaches to characterise microbial responses to salt exposure have so far been microbial biomass and respiration measurements. We compile datasets from a selection of studies and find that (1) microbial biomass-carbon (C) per C held in soil organic matter shows no consistent pattern with long-term (field gradients) or short-term (laboratory additions) soil salinity level, and (2) respiration per soil organic C is substantially inhibited by higher salt concentrations in soil, and consistently so for both short-term and long-term salinity levels. Patterns that emerge from extra-cellular enzyme assessments are more difficult to generalize, and appear to vary with the enzyme studied, and its context. Growth based assessments of microbial responses to salinization are largely lacking. Relating the established responses of microbial respiration to that of growth could provide an estimate for how the microbial C-use efficiency would be affected by salt exposure. This would be a valuable predictor for changes in soil C sequestration. A few studies have investigated the connection between microbial tolerance to salt and the soil salinity levels, but so far results have not been conclusive. We predict that more systematic inquiries including comprehensive ranges of soil salinities will substantiate a connection between soil salinity and microbial tolerance to salt. This would confirm that salinity has a direct effect on the composition of microbial communities. While salt has been identified as one of the most powerful environmental factors to structure microbial communities in aquatic environments, no up-to-date sequence based assessments currently exist from soil. Filling this gap should be a research priority. Moreover, linking sequencing based assessments of microbial communities to their tolerance to salt would have the potential to yield biomarker sets of microbial sequences. This could provide predictive power for, e.g., the sensitivity of agricultural soils to salt exposure, and, as such, a useful tool for soil resource management. We conclude that salt exposure has a powerful influence on soil microbial communities and processes. In addition to being one of the most pressing agricultural problems to solve, this influence could also be used as an experimental probe to better understand how microorganisms control the biogeochemistry in soil.     

Soil microbial biomass and community composition as affected by cover crop diversity in a short‐term field experiment on a podzolized Stagnosol‐Cambisol

Background: Cover cropping appears as a useful land management practice with numerous benefits for ecosystem functions. Aim: The objectives of this study were to determine the effects of different winter cover crops on soil microbial biomass, activity, and community composition in intensively managed agriculture systems as function of cover crop diversity. Methods: For this purpose, an on‐farm experiment was conducted at a podzolized Stagnosol‐Cambisol during seven months growing oil radish as single cover crop and five different cover crop mixtures comprising 5 to 13 plant species. A fallow treatment was used as control. Phospholipid fatty acids were used to determine the soil microbial biomass and soil microbial community composition. Basal respiration of the soil microorganisms was measured as a proxy for microbial activity. Results: The results show that none of the cover crop mixture could increase soil organic carbon or total nitrogen content. Three cover crop mixtures and oil radish as single cover crop significantly increased soil microbial biomass by about 50% and all of the investigated cover crops significantly increased microbial respiration and metabolic quotient by 50–150%. Only highly diverse cover crop mixtures significantly increased individual microbial groups such as Gram‐positive and Gram‐negative bacteria, actinobacteria, and saprotropic and mycorrhizal fungi by about 20% compared to the control. However, the ratio of fungi to bacteria was not influenced by any of the cover crop mixtures under study. Conclusion: These findings corroborate that aboveground plant diversity is linked to belowground microbial diversity.     

<Emphasis Type="Italic">Trichoderma</Emphasis> inoculation and trash management effects on soil microbial biomass,soil respiration,nutrient uptake and yield of ratoon sugarcane under subtropical conditions

A field experiment was conducted during 2003–2005 and 2004–2006 at the Indian Institute of Sugarcane Research, Lucknow, India to study the effect of Trichoderma viride inoculation in ratoon sugarcane with three trash management practices, i.e. trash mulching, trash burning and trash removal. Trichoderma inoculation with trash mulch increased soil organic carbon and phosphorus (P) content by 5.08 Mg ha⁻¹ and 11.7 kg ha⁻¹ over their initial contents of 15.75 Mg ha⁻¹ and 12.5 kg ha⁻¹, respectively. Soil compaction evaluated as bulk density in 0- to 15-cm soil layer, increased from 1.48 Mg m⁻³ at ratoon initiation (in April) to 1.53 Mg m⁻³ at harvest (in December) due to trash burning and from 1.42 Mg m⁻³ at ratoon initiation (in April) to 1.48 Mg m⁻³ at harvest (in December) due to trash mulching. The soil basal respiration was the highest during tillering phase and then decreased gradually, thereafter with the advancement of crop growth. On an average, at all the stages of crop growth, Trichoderma inoculation increased the soil basal respiration over no inoculation. Soil microbial biomass increased in all plots except in the plots of trash burning/removal without Trichoderma inoculation. The maximum increase (40 mg C kg⁻¹ soil) in soil microbial biomass C, however, was observed in the plots of trash mulch with Trichoderma inoculation treatment which also recorded the highest uptake of nutrient and cane yield. On an average, Trichoderma inoculation with trash mulch increased N, P and K uptake by 15.9, 4.68 and 23.6 kg ha⁻¹, respectively, over uninoculated condition. The cane yield was increased by 12.8 Mg ha⁻¹ with trash mulch + Trichoderma over trash removal without Trichoderma. Upon degradation, trash mulch served as a source of energy for enhanced multiplication of soil bacteria and fungi and provided suitable niche for plant–microbe interaction.