Long-term no-till management affects microbial biomass but not community composition in Canadian prairie agroecosytems

No-till (NT) management greatly reduces soil physical disturbance and can result in a stratification of nutrients and organic matter in the soil profile due to the retention of crop residues on the soil surface potentially affecting the dynamics of microbial interactions in the soil. Microbial abundance and diversity can be used to assess the relative impact of management on the long-term sustainability of cropping systems. The objective of this study was to assess the impact of long-term NT vs. conventional tillage (CT) management on soil microbial community structure at four different sites on the Canadian prairies using phospholipid fatty acid analysis (PLFA) and DNA fingerprinting. Analysis of 16S and 18S rDNA using denaturing gradient gel electrophoresis revealed high inherent variability within bacterial and fungal community fingerprints among replicate field plots. Differences in bacterial and fungal phylogeny were related to depth in the soil profile but not to tillage management. Abundance of individual PLFA biomarkers were 7 to 86% greater in NT surface soils (0- to 5-cm depth), except at the Ellerslie site in 2005 where biomass was greater in CT. Responses at the 5- to 10-cm and 10- to 15-cm depths were more varied, in some cases with greater biomass in CT than NT soils. Ordination analysis of PLFA profiles showed clear community separation with depth but not tillage. Physiological stress biomarkers were correlated with simple measures of nutrient concentration and indicated that resource availability was likely the main factor determining community structure. It was concluded that tillage disturbance was not an overriding factor in determining microbial community composition in the long-term NT and CT soils studied. Further study of the interaction of cropping frequency with tillage management is needed to understand the effects of tillage disturbance on microbial turnover of plant derived residues.     

Seasonal variation of microbial biomass, activity, and community structure in soil under different tillage and phosphorus management practices

No-tillage systems contribute to physical, chemical and biological changes in the soil. The effects of different tillage practices and phosphorus (P) fertilization on soil microbial biomass, activity, and community structure were studied during the maize growing season in a maize–soybean rotation established for 18 years in eastern Canada. Soil samples were collected at two depths (0–10 and 10–20 cm) under mouldboard plow (MP) and no-till (NT) management and fertilized with 0, 17.5, and 35 kg P ha^?1. Results show that the duration of the growing season had a greater effect on soil microbiota properties than soil tillage or P fertilization at both soil depths. Seasonal fluctuations in soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N), in dehydrogenase and alkaline phosphomonoesterase activities, and in total phospholipids fatty acid (PLFA) level, were greater under NT than MP management. The PLFA biomarkers separated treatments primarily by sampling date and secondly by tillage management, but were not significantly affected by P fertilization. The abundance of arbuscular mycorrhizal fungi (AMF; C16:1ω5) and fungi (C18:2ω6,9) was lower under NT than MP at the 10–20-cm soil depth in July. Phosphorus fertilization increased soil microbial biomass phosphorus (SMB-P) and Mehlich-3 extractable P, but had a limited impact on the other soil properties. In conclusion, soil environmental factors and tillage had a greater effect on microorganisms (biomass and activity) and community structure than P fertilization.     

Short-term effect of tillage and crop rotation on microbial community structure and enzyme activities of a clay loam soil

A field study was carried out to analyze the short-term (2 years) effect of tillage and crop rotation on microbial community structure and enzyme activities of a clay loam soil. The experimental design was a split-plot arrangement of treatments, consisting of two tillage treatments—ridge tillage (RT) and no-tillage (NT)—in combination with two crop rotation treatments—corn (Zea mays L.) monoculture and a 2-year corn-soybean (Glycine max L.) rotation. Phospholipid fatty acid (PLFA) profiles were used to assess soil microbial community structure. No-tillage resulted in significantly higher total PLFAs compared to the RT treatment, which was accompanied by higher activities of protease, β-glucosaminidase, and β-glucosidase. This suggests a close link between soil microbial communities and enzyme activities in response to tillage. The increase of total microbial lipid biomass in the NT soils was due to the increase in both fungal and bacterial PLFAs. Crop rotation had little effect on soil bacterial communities and enzyme activities, but it significantly influenced soil fungal communities, particularly arbuscular mycorrhizal fungi. Soils under monoculture corn had higher fungal biomass than soils under corn-soybean rotation regardless of tillage treatment.     

Contributions of soil biota to C sequestration varied with aggregate fractions under different tillage systems

It is increasingly believed that substantial soil organic carbon (SOC) can be sequestered in conservation tillage system by manipulating the functional groups of soil biota. Soil aggregates of different size provide diverse microhabitats for soil biota and consequently influence C sequestration. Our objective was to evaluate the contributions of soil biota induced by tillage systems to C sequestration among different aggregate size fractions. Soil microbial and nematode communities were examined within four aggregate fractions: large macroaggregates (>2 mm), macroaggregates (2–1 mm), small macroaggregates (1–0.25 mm) and microaggregates (<0.25 mm) isolated from three tillage systems: no tillage (NT), ridge tillage (RT) and conventional tillage (CT) in Northeast China. Soil microbial and nematode communities varied across both tillage systems and aggregate fractions. The activity and abundance of microbes and nematodes were generally higher under NT and RT than under CT. Among the four aggregate fractions, soil microbial biomass and diversity were higher in microaggregates, while soil nematode abundance and diversity were higher in large macroaggregates. Structural equation modelling (SEM) revealed that the linkage between microbial and nematode communities and their contributions to soil C accumulation in >1 mm aggregate fractions were different from those in <1 mm aggregate fractions. Higher abundance of arbuscular mycorrhizal fungi (AMF) could enhance C retention within >1 mm aggregates, while more gram-positive bacteria and plant-parasitic nematodes might increase C accumulation within <1 mm aggregates. Our findings suggested that the increase in microbial biomass and nematode abundance and the alteration in their community composition at the micro-niche within aggregates could contribute to the higher C sequestration in conservation tillage systems (NT and RT).     

Effects of short-term conservation management practices on soil organic carbon fractions and microbial community composition under a rice-wheat rotation system

The objective of this study was to investigate the effects of short-term (less than 2 years) conservation managements [no-tillage (NT) and crop residue returning] on top soil (0–5 cm) microbial community composition and soil organic C (SOC) fractions under a rice-wheat rotation at Junchuan town of Hubei Province, China. Treatments were established following a split-plot design of a randomized complete block with tillage practices [conventional tillage (CT) and NT] as the main plot and residue returning level [no residue returning (0) and all residues returned to fields from the preceding crop (S, 2,146 kg C ha^?1)] as the subplots. The four treatments were CT with or without residue returning (CT0 and CTS) and NT with or without residue returning (NT0 and NTS). The abundances of microbial groups [total FLFAs, fungal biomass, bacterial biomass, fungal biomass/bacterial biomass (F/B), monounsaturated fatty acids/saturated fatty acids (MUFA/STFA), and microbial stress] were determined by phospholipid fatty acid (PLFA) analysis of soil. The ratio of MUFA/STFA reflects aeration of soil and greater MUFA/STFA means better aeration condition of soil. Moreover, the microbial stress, the ratio of cy19:0 to 18:1ω7, was regarded as an indicator of physiological or nutritional stress of microbial community. PLFA profiles were dominated by the fatty acids iC15:0 (9.8 %), C16:0 (16.5 %), 10Me17:0 (9.9 %), and Cyc19:0 (8.3 %), together accounting for 44.6 % of the total PLFAs. Compared with CT, NT significantly increased microbial biomass C (MBC) by 20.0 % but did not affect concentrations of total organic C (TOC), dissolved organic C (DOC), easily oxidizable C (EOC), and SOC of aggregates. Residue returning significantly increased MBC by 18.3 % and SOC content of 2–1-mm aggregate by 9.4 %. NT significantly increased total PLFAs by 9.8 % and fungal biomass by 40.8 % but decreased MUFA/STFA by 15.5 %. Residue returning significantly enhanced total PLFAs, bacterial biomass, fungal biomass, F/B, and MUFA/STFA by 31.1, 36.0, 95.9, 42.5, and 58.8 %, respectively, but decreased microbial stress by 45.9 %. Multivariate analysis (redundancy analysis and partial correlation analysis) indicated that SOC of 2–1-mm aggregate was related to changes in the composition of soil microbial groups, suggesting that SOC of 2–1-mm aggregate was sensitive to changes in soil microbial community composition affected by short-term conservation management practices in our study.     

Dynamics of soil biota at different depths under two contrasting tillage practices

One aim of conservation tillage is to preserve soil biological properties. This study was conducted to examine the effects of two contrasting tillage treatments on soil biota at different depths. We investigated the population dynamics and vertical distributions of microbes and several soil faunal groups for 2 years in field Andosols in northeastern Japan. The experimental plots were under no tillage (NT) or conventional tillage (CT, rotary tilled to 20 cm) management. In the 0–10-cm soil layer, bacterial and fungal substrate-induced respiration (SIR) and the population density of enchytraeids were higher under NT than under CT, but the population densities of protozoa, mites, and collembolans did not differ significantly. In contrast, at 10–20 cm, both SIR values were higher under CT, where larger populations of mites and collembolans were recorded. At both depths, nematodes were more abundant under CT. Thus, the effects of tillage on these soil organisms differed according to soil depth, and negative impacts of tillage were smaller in the deeper layer. Larger amounts of earthworm casts at the soil surface in NT plots showed a greater biomass of earthworms than in CT. To evaluate the activities of soil biota, we buried litterbags with three different mesh sizes at the two depths and examined the rate of decomposition. The daily decay constant of litter in the surface soil layer (1.5–8.5 cm) was greater under NT. We suppose that the activities of soil biota in this layer were stimulated under NT, and that especially microbes and enchytraeids, which were abundant at 0–10 cm, contributed greatly to the decomposition.     

免耕秸秆还田和传统耕作方式下东北黑土氨基糖态碳的积累特征

以吉林德惠市中层黑土进行7年田间定位试验的小区土壤为研究对象,对免耕(NT)和传统耕作下(CT)耕层(0～20 cm)氨基糖态碳含量的变化特征进行了分析。结果表明,与传统耕作相比,实施免耕7年后整个耕层土壤中氨基糖态碳含量显著增加(p<0.05),以表层(0～5 cm)增加幅度最大,高达94.7%。说明在研究地区,免耕措施有利于微生物代谢物如细胞壁物质等作为潜在的碳源逐渐积累在土壤中。免耕土壤中不同微生物来源氨基糖态碳的含量均较传统耕作有显著增加,但是变化特征有所不同,其中免耕条件下真菌来源的氨基葡萄糖的积累量较传统耕作高出1倍多,而且氨基葡萄糖与细菌来源的胞壁酸的比值(6.9～7.3)显著高于传统耕作(4.7～5.4),暗示实施免耕秸秆还田7年后土壤中真菌已逐渐转为优势群体,而真菌占优势的农田生态系统具有更大的固碳潜力。     

Soil microbial community composition as affected by restoration practices in California grassland

Agricultural practices have strong impacts on soil microbes including both the indices related to biomass and activity as well as those related to community composition. In a grassland restoration project in California, where native perennial bunchgrasses were introduced into non-native annual grassland after a period of intensive tillage, weeding, and herbicide use to reduce the annual seed bank, microbial community composition was investigated. Three treatments were compared: annual grassland, bare soil fallow, and restored perennial grassland. Soil profiles down to 80 cm in depth were investigated in four separate layers (0-15, 15-30, 30-60, and 60-80 cm) using both phospholipid ester-linked fatty acid (PLFAs) and ergosterol as biomarkers in addition to microbial biomass C by fumigation extraction. PLFA fingerprinting showed much stronger differences between the tilled bare fallow treatment vs. grasslands, compared to fewer differences between restored perennial grassland and annual grassland. The presence or absence of plants over several years clearly distinguished microbial communities. Microbial communities in lower soil layers were little affected by management practices. Regardless of treatment, soil depth caused a strong gradient of changing habitat conditions, which was reflected in Canonical Correspondence Analysis of PLFAs. Fungal organisms were associated with the presence of plants and/or litter since the total amount and the relative proportion of fungal markers were reduced in the tilled bare fallow and in lower layers of the grassland treatments. Total PLFA and soil microbial biomass were highly correlated, and fungal PLFA biomarkers showed strong correlations to ergosterol content. In conclusion, microbial communities are resilient to the grassland restoration process, but do not reflect the change in plant species composition that occurred after planting native bunchgrasses.     

Contrasting development of soil microbial community structure under no-tilled perennial and tilled cropping during early pedogenesis of a Mollisol

A range of agricultural practices influence soil microbial communities, such as tillage and organic C inputs, however such effects are largely unknown at the initial stage of soil formation. Using an eight-year field experiment established on exposed parent material (PM) of a Mollisol, our objectives were to: (1) to determine the effects of field management and soil depth on soil microbial community structure; (2) to elucidate shifts in microbial community structure in relation to PM, compared to an arable Mollisol (MO) without organic amendment; and (3) to identify the controlling factors of such changes in microbial community structure. The treatments included two no-tilled soils supporting perennial crops, and four tilled soils under the same cropping system, with or without chemical fertilization and crop residue amendment. Principal component (PC) analysis of phospholipid fatty acid (PLFA) profiles demonstrated that microbial community structures were affected by tillage and/or organic and inorganic inputs via PC1 and by land use and/or soil depth via PC2. All the field treatments were separated by PM into two groups via PC1, the tilled and the no-tilled soils, with the tilled soils more developed towards MO. The tilled soils were separated with respect to MO via PC1 associated with the differences in mineral fertilization and the quality of organic amendments, with the soils without organic amendment being more similar to MO. The separations via PC1 were principally driven by bacteria and associated with soil pH and soil C, N and P. The separations via PC2 were driven by fungi, actinomycetes and Gram (−) bacteria, and associated with soil bulk density. The separations via both PC1 and PC2 were associated with soil aggregate stability and exchangeable K, indicating the effects of weathering and soil aggregation. The results suggest that in spite of the importance of mineral fertilization and organic amendments, tillage and land-use type play a significant role in determining the nature of the development of associated soil microbial community structures at the initial stages of soil formation.     

Microbial properties and nitrogen contents of arable soils under different tillage regimes

Attention is being paid to the use of different tillage regimes as a means of retaining soil organic carbon (SOC) and sequestering more SOC. Alongside earlier measurements of total SOC stocks under different tillage regimes, we have examined the distribution of nitrogen (N), microbial activity and the structure of the soil bacterial community from differently tilled plots under continuous barley. The plots were established 5 yr before sampling and have been maintained annually under conventional tillage (CT; moldboard ploughing to 20 cm and disking), deep ploughing (DP; ploughing to 40 cm and disking), minimum tillage (MT; disking to 7 cm) or zero tillage (ZT). Our earlier work showed there was no difference in SOC contents down to 60‐cm depth between the treatments, but now we report that there were significant differences in the total N and active microbial biomass (substrate‐induced respiration) contents of the same soils. The N contents of the CT, DP and MT treatments were not significantly different, but the ZT contained significantly more N, indicating either greater N retention under the ZT treatment or preferential loss from the more intensively tilled treatments, or a combination of both. The microbial biomass content was greater for the CT and DP treatments than for the MT and ZT treatments, indicating greater sensitivity to treatment effects of the microbial biomass pool than the total C pool, consistent with its more dynamic nature. Terminal restriction fragment length polymorphism (T‐RFLP) analyses of the soil bacteria DNA (a method of assessing the bacterial community structure) enabled the samples to be distinguished both according to SOC content, which is to be expected, and to tillage regime with the greatest differences in community structure occurring in the ZT treatment and the least in DP and CT treatments, reflecting the degree of homogenization or disturbance resulting from tillage.     

Influence of reduced tillage on earthworm and microbial communities under organic arable farming

Although reduced tillage is an agricultural practice reported to decrease soil erosion and external inputs while enhancing soil fertility, it has still rarely been adopted by European organic farmers. The objective of this study was to assess the long-term interactive effects of tillage (conventional (CT) vs. reduced (RT)) and fertilization (slurry (S) vs. composted manure/slurry (MCS)) on earthworms and microbial communities in a clay soil under spelt in an organic 6-year crop rotation. Earthworm populations (species, density and biomass, cocoons) were investigated by handsorting the soil nine years after initial implementation of the treatments. Soil microbial carbon (C_mic) and nitrogen (N_mic) were measured by chloroform-fumigation extraction and a simplified phospholipid fatty acid (PLFA) analysis was used to separate for populations of bacteria, fungi and protozoa. Significantly increased total earthworm density in RT plots was mainly attributed to increased numbers of juveniles. Moreover, we found five times more cocoons with RT. Species richness was not affected by the treatments, but tillage treatments had differentially affected populations at the species-level. In addition, cluster analysis at the community level revealed two distinct groups of plots in relation to tillage treatments. In RT plots C_mic increased in the 0–10 cm and 10–20 cm soil layers, while PLFA concentrations indicative of Gram-negative bacteria, fungi and protozoa only increased in the topsoil. Lower bacteria-to-fungi ratios in the upper soil layer of RT plots indicated a shift to fungal-based decomposition of organic matter whereas a higher C_mic-to-C_org ratio pointed towards enhanced substrate availability. Slurry application decreased microbial biomass and enhanced density of juvenile anecic earthworms but overall fertilization effect was weak and no interactions with tillage were found. In conclusion, tillage is a major driver in altering communities of earthworms and microorganisms in arable soils. The use of reduced tillage provides an approach for eco-intensification by enhancing inherent soil biota functions under organic arable farming.     

Bacterial diversity in water-stable aggregates of soils under conventional and zero tillage management

Reduced tillage of agricultural soils has been shown to result in greater macroaggregation, microbial biomass and microbial diversity. While it has been shown that macroaggregates contain more microbial biomass per unit soil mass than microaggregates, it is unclear how microbial diversity varies with soil aggregation. We investigated the functional diversity (catabolic potential) of bacteria, evaluated by calculating Shannon’s diversity index (H′), substrate richness (S) and substrate evenness (E) from potential substrate utilization patterns, in whole soil (i.e. not separated into different aggregate sizes) and aggregates of different sizes (2–4, 1–2, 0.5–1, 0.25–0.5, and 0.1–0.25 mm diameter) in loam and silt loam soils grown to barley and managed for 6 years under conventional tillage (CT) or zero tillage (ZT) systems in northern British Columbia. There were no significant tillage effects on bacterial diversity in whole soils. In soil aggregates, H′ and E were significantly higher under CT than under ZT on the loam at barley planting time, with no significant aggregate size effects. However, at barley-heading stage, all diversity indices in both soils were significantly higher under ZT than under CT, and they tended to increase with increasing aggregate size. Cluster analysis and principal component analysis of substrate utilization patterns also revealed differences in bacterial community structures between CT and ZT, but the substrates that were utilized differently between the two tillage systems were not the same between soil types or sampling times. The results during the cropping cycle imply that deterioration of soil structure is probably one factor that explains the adverse effects of soil tillage on soil microbial biomass and diversity.     

稻田系统管理措施对微生物生物量C、N、P的长期影响

A 12-year field experiment was conducted to investigate the effect of different tillage methods and fertil-ization systems on microbial biomass C,N and P of a gray fluvo-aguic soil in rice-based cropping system .Five fertilization treatments were designed under conventional tillae(CT) or on tillage(NT) system:no fertilizer(CK) ; chemical fertilizer only(CF) ; combining chemical fertilizer with pig manure(PM); combining chemical fertilizer with crop straw (CS) and fallow (F). The results showed that biomass C,N and P were enriched in the surface layer of no-tilled soil,whereas they distributed relatively evenly in the tilled soil,which might result from enrichment of crop resdue,organic manure and mineral fertilzer,and surficial developent of root systems under NT.Under the cultivation system NT had slightly greater biomass C,N and P at 0-5 cm depth ,significantly less biomass C,N and P at 5-15 cm depth ,less microbial biomass C,N and equivalent biomass P at 15-30 cm depth as compared to CT,indicating hat tillage was beneficial for the multiplication of organims in the plowed layer of soil.Under the fallow system,biomass C,N and P in the surface layer were significantly greater for NT than CT while their differences between the two tillage methods were neligible in the deeper layers.In the surface layer,biomass C,N and P in the soils amended with oranic manure combined with mineral fertilizers were significantly greater than those of the treatments only with mineral fertilizers and the control.Soils without fertilzer had the least biomass nutrient contents among the five fertilization treatments.Obviously,the long-term application of organic manure could maintain the higher activity of microorganisms in soils.The amounts of biomass C,N and P in the fallowed soils varied with the tillage methods;they were much greater under NT than under CT,especially in the surface layer,suggesting that the frequent plowing could decrease the content of organic matter in the surface layer of the fallowed soil.     

土壤微生物群落结构与多样性对农田集约化管理程度降低的响应

Using a scheme of agricultural fields with progressively less intensive management （deintensification）, different management practices in six agroecosystems located near Goldsboro, NC, USA were tested in a large-scale experiment, including two cash-grain cropping systems employing either tillage （CT） or no-tillage （NT）, an organic farming system （OR）, an integrated cropping system with animals （IN）, a successional field （SU）, and a plantation woodlot （WO）. Microbial phospholipid fatty acid （PLFA） profiles and substrate utilization patterns （BIOLOG ECO plates） were measured to examine the effects of deintensification on the structure and diversity of soil microbial communities. Principle component analyses of PLFA and BIOLOG data showed that the microbial community structure diverged among the soils of the six systems.Lower microbial diversity was found in lowly managed ecosystem than that in intensive and moderately managed agroecosystems, and both fungal contribution to the total identified PLFAs and the ratio of microbial biomass C/N increased along with agricultural deintensification. Significantly higher ratios of C/N （P 〈 0.05） were found in the WO and SU systems, and for fungal/bacterial PLFAs in the WO system （P 〈 0.05）. There were also significant decreases （P 〈 0.05） along with agricultural deintensification for contributions of total bacterial and gram positive （G＋） bacterial PLFAs.Agricultural deintensification could facilitate the development of microbial communities that favor soil fungi over bacteria.     

Microbial activity,community structure and potassium dynamics in rhizosphere soil of soybean plants treated with glyphosate

With the advent of glyphosate [N-(phosphonomethyl)glycine] tolerant crops, soils have now been receiving repeated applications of the herbicide for over 10 years in the Midwestern USA. There is evidence that long-term use of glyphosate can cause micronutrient deficiency but little is known about plant potassium (K) uptake interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect soil K dynamics and ultimately K availability for crops. Therefore, the objectives of this study were to characterize the effect of foliar glyphosate applied to GR (glyphosate resistant) soybeans on: (1) rhizosphere microbial community profiles using ester linked fatty acid methyl ester (EL-FAME) biomarkers, (2) exchangeable, non-exchangeable, and microbial K in the rhizosphere soil, and (3) concentrations of soybean leaf K. A greenhouse study was conducted in a 2 × 2 × 3 factorial design with two soil treatments (with or without long-term field applications of glyphosate), two plant treatments (presence and absence of soybean plants), and three rates of glyphosate treatments (0×, 1× at 0.87, and 2× at 1.74 kg ae ha^?1, the recommended field rate). After each glyphosate application, rhizosphere soils were sampled and analyzed for microbial community structure using ester linked fatty acid methyl ester biomarkers (EL-FAME), and exchangeable, plant tissue and microbial biomass K. Glyphosate application caused a significant decrease in the total microbial biomass in soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application. However, no significant changes were observed in the overall microbial community structure. In conclusion, the glyphosate application lowered the total microbial biomass in the GR soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application; caused no changes in the microbial community structure; and did not reduce the plant available K (soil exchangeable or plant tissue K).     

稻麦轮作条件下长期不同土壤管理对供氮能力的影响

通过种植了 25季的长期定位试验研究了稻麦轮作条件下不同土壤耕作方式和培肥制度对土壤供氮能力的影响。结果表明 ,不论免耕还是耕翻 ,0～5cm土壤的氮素释放均较持久 ,5～15cm土壤的氮素释放耕翻较免耕持久。休闲的 0～5cm土壤在免耕条件下其氮素矿化势和短期矿化氮量均远远高于耕翻 ,5～15cm和 15～30cm土壤在免耕和耕翻间则相差不大。施肥的3个处理 0～ 5cm土壤氮素矿化势和短期矿化氮量有免耕高于耕翻的趋势 ,而 5～ 15cm土层免耕明显低于耕翻 ,15～ 30cm土壤免耕与耕翻没有差异。有机肥与化肥配施的免耕与耕翻土壤中 25季作物吸氮量几乎无差异 ,不施肥和单施化肥处理的免耕土壤中作物吸氮量低于耕翻土壤。免耕条件下 ,有机肥配施化肥土壤的供氮能力仅低于休闲土壤 ,不施肥土壤最低 ;耕翻条件下 ,有机肥配施化肥土壤的供氮能力最高。各培肥处理间的差异主要表现在 0～ 5cm土层。     

Soil texture affects soil microbial and structural recovery during grassland restoration

Many biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.     

Physical, chemical and microbiological properties of an Andisol as related to land use and tillage practice

The effects of land use and management practice on soil physical, chemical and microbiological properties may provide essential information for assessing sustainability and environmental impact. This study compared the effects of 41 years of no-tillage (NT) with continuous apple orchard, with those of conventional tillage (CT) with wheat–soybean rotation and another of puddling (PD) with continuous rice on the characteristics of a pumice Andisol in a temperate region of northern Japan. Higher values for bulk density, penetration resistance, pH, C/N ratio, exchangeable Na (X-Na), Fe, and Mn were observed for PD than NT and CT. On the other hand, organic matter, EC, N, exchangeable K (X-K), exchangeable Ca (X-Ca) and Cu were significantly higher for NT than CT and PD. Highest content of Zn was found in CT compared to other practices. The three-phase composition at pF 2.0 was significantly affected by land use and tillage practices. The solid phase and liquid phase were greater under PD than under NT and CT, while air phase was greater under CT than under NT and PD. Significantly higher values for saturated hydraulic conductivity was found in CT than NT and PD. Total phospholipid fatty acid (PLFA) and PLFA for bacteria, aerobes and cyanobacteria were remarkably higher in NT than CT and PD, regardless of depth. On the other hand, PLFA for methane-oxidizing bacteria, sulfate-reducing bacteria and mycorrhizae were significantly higher in CT than NT and PD. PLFA for fungi was significantly higher in surface (0–10 cm) soils than subsurface (10–20 cm) soils regardless of treatments. Highest bacterial and fungal diversity evaluated by DNA band number in DGGE analysis based on PCR amplification of 16S rDNA and 18S rDNA fragments, respectively, were observed in surface soil of PD. The result suggests a linkage between microbial community and tillage practices in temperate Andisol. This study also justifies the need of measuring soil characteristics based on soil microbial communities.     

Characterizing the relationships between soil organic matter components and microbial function and composition along a tillage disturbance gradient

We studied the effect of no-till (disc seeder), conventional-till (tine scarifier+disc seeder) and rotary-till (rotary hoe+disc seeder) management on soil organic matter (SOM) components, rates of carbon (C) and nitrogen (N) cycling, substrate utilization and microbial community composition. We hypothesized that labile SOM fractions are sensitive to changes in tillage techniques and, in turn mediate any tillage-induced changes in microbial function and composition. A replicated field site was established in May 1998 in the semi-arid agricultural region of Western Australia and soils were collected in September 2004. We found soil pH varied between different tillage techniques as an initial lime application was mixed to deeper soil depths in rotary-till soil than no-till and conventional-till soil. Total-C was greater in surface soil and lower in subsurface soil from no-till and conventional-till plots than from rotary-till plots, but there was no effect of tillage technique on total-C when averaged across soil depths. Light (specific density <1.0 g cm^?3) fraction organic matter (LFOM), dissolved organic matter (DOM) and microbial biomass (MB) C and N pools, and rates of C and N cycling all tended to decrease with soil depth. In general, LFOM-C and N, dissolved organic C (DOC) and microbial biomass carbon (MB-C), soil respiration, cellulase activity, gross immobilization rates were positively correlated (r>0.50) and were greater in no-till and conventional-till soil than rotary-till soil both within, and across soil depths. These soil variables generally increased (r>0.5) with increasing soil pH. Dissolved organic N and gross N mineralization were positively correlated (r>0.90) but neither was affected by tillage techniques. No-till soil had greater utilization of carboxylic acids and lower utilization of amino acids and carbohydrates than conventional-till and rotary-till soil; surface soil also had greater utilization of carboxylic acids than subsurface soil. In turn, substrate utilization differed between soil depths, and between no-till soil and conventional-till and rotary-till soil; these differences were correlated with soil pH, total-N, DOC, LFOM-N and microbial biomass nitrogen (MB-N). Bacterial and fungal biomasses generally decreased with soil depth and were greater in no-till and conventional-till soil than rotary-till soil. Microbial community composition differed between all tillage techniques and soil depths; these differences were correlated with soil textural classes, soil pH, and total, LFOM, DOM and microbial C and N pools. These results indicate that most tillage-induced changes to soil properties were associated with the greater soil disturbance under rotary-till than under no-till or conventional-till management. Our results indicate that tillage-induced changes to soil pH, and LFOM, DOM and microbial biomass pools are likely to be important regulators of the rates of C and N cycling, substrate utilization and microbial community composition in this coarse textured soil.     

Soil microbial community responses to dairy manure or ammonium nitrate applications

Soil management practices that result in increased soil C also impact soil microbial biomass and community structure. In this study, the effects of dairy manure applications and inorganic N fertilizer on microbial biomass and microbial community composition were determined. Treatments examined were a control with no nutrient additions (CT), ammonium nitrate at 218 kg N ha⁻¹ (AN), and manure N rates of 252 kg manure-N ha⁻¹ (LM) and 504 kg manure-N ha⁻¹ (HM). All plots were no-till cropped to silage corn (Zea mays, L. Merr) followed by a Crimson clover (Trifolium incarnatum, L.)/annual ryegrass (Lolium multiflorum, Lam.) winter cover crop. Treatments were applied yearly, with two-thirds of the N applied in late April or early May, and the remainder applied in September. Soil samples (0–5, 5–10, and 10–15 cm) were taken in March 1996, prior to the spring nutrient application. Polar lipid fatty acid (PLFA) analysis was used to assess changes in microbial biomass and community structure. Significantly greater soil C, N and microbial biomass in the 0–5 cm depth were observed under both manure treatments than in the CT and AN treatments. There was also a definable shift in the microbial community composition of the surface soils (0–5cm). Typical Gram-negative bacteria PLFA biomarkers were 15 and 27% higher in the LM and HM treatments than in the control. The AN treatment resulted in a 15% decrease in these PLFA compared with the control. Factor analysis of the polar lipid fatty acid profiles from all treatments revealed that the two manure amendments were correlated and could be described by a single factor comprised of typical Gram-negative bacterial biomarkers. The AN treatments from all three depths were also correlated and were described by a second factor comprised of typical Gram-positive bacterial biomarkers. These results demonstrate that soil management practices, such as manuring, that result in accumulations of organic carbon will result in increased microbial biomass and changes in community structure.