Crop yield and soil fertility response to reduced tillage under organic management

Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm. This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (C_org), microbial biomass (C_mic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the components tested, only tillage had any influence on these soil fertility indicators. C_org in the 0–10 cm soil layer increased by 7.4% (1.5 g C_org kg⁻¹ soil, p < 0.001) with reduced tillage between 2002 and 2005, but remained constant with conventional tillage. Similarly, C_mic was 28% higher and DHA 27% (p < 0.001) higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there were no significant differences for these soil parameters between the tillage treatments. Tillage had no significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower (Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat yield by 5% (p < 0.001) compared to compost fertilization. Overall, C_org, C_mic, and DHA improved and yields showed only a small reduction with reduced tillage under organic management, but long-term effects such as weed competition remain unknown.     

Soil organic matter stratification ratio as an indicator of soil quality

Soil quality is a concept based on the premise that management can deteriorate, stabilize, or improve soil ecosystem functions. It is hypothesized that the degree of stratification of soil organic C and N pools with soil depth, expressed as a ratio, could indicate soil quality or soil ecosystem functioning, because surface organic matter is essential to erosion control, water infiltration, and conservation of nutrients. Stratification ratios allow a wide diversity of soils to be compared on the same assessment scale because of an internal normalization procedure that accounts for inherent soil differences. Stratification ratios of soil organic C were 1.1, 1.2 and 1.9 under conventional tillage (CT) and 3.4, 2.0 and 2.1 under no tillage (NT) in Georgia, Texas, and Alberta/British Columbia, respectively. The difference in stratification ratio between conventional and NT within an environment was inversely proportional to the standing stock of soil organic C to a depth of 15–20 cm across environments. Greater stratification of soil C and N pools with the adoption of conservation tillage under inherently low soil organic matter conditions (i.e., warmer climatic regime or coarse-textured soil) suggests that standing stock of soil organic matter alone is a poor indication of soil quality. Stratification of biologically active soil C and N pools (i.e., soil microbial biomass and potential activity) were equally or more sensitive to tillage, cropping intensity, and soil textural variables than stratification of total C and N. High stratification ratios of soil C and N pools could be good indicators of dynamic soil quality, independent of soil type and climatic regime, because ratios >2 would be uncommon under degraded conditions.     

Effects of soil compaction on N-mineralization and microbial-C and -N. I. Field measurements

Soil biological parameters, such as soil respiration or N-mineralization, may be more sensitive to soil compaction than physical parameters. Therefore we studied the effects of soil compaction on net N-mineralization and microbial biomass dynamics in the field. The soils were silty clay loams (Typic Endoaquepts) in either a well-structured permanent pasture with high organic-C content (46 mg g⁻¹) or a site which had been continuously cropped with cereals for 28 years with low organic-C content (21 mg g⁻¹) and a very poor structure. Compaction treatments were applied by five passes of a tractor (total weight 4880 kg, speed 2.2 m s⁻¹). An energy flux of either 2712 J m⁻² (assuming deflecting tyres) or 6056 J m⁻² (assuming rigid tyres) per pass of the rear tyres was estimated. Soil dry bulk densities were initially 1.00 and 1.30 Mg m⁻³ in the pasture and cropped sites, respectively, and increased significantly only in the less dense pasture site. However, soil surface CO₂-fluxes decreased substantially after compaction on both sites (57–69%) because of the highly reduced air permeability of the topsoil. At the cropped site this was also accompanied by a significant decrease in oxygen-diffusion rate (45%). Using the in situ core technique with covered cores the apparent net N-mineralization rate was less in compacted than in non-compacted areas of the pasture ((0.27 and 0.38 μg N g⁻¹ day⁻¹, respectively), but did not differ at the cropped site (average 0.15 μg N g⁻¹ day⁻¹). However, N-mineralization measurements by the in situ core technique were found to be problematic as denitrification possibly occurred and concealed actual net N-mineralization. Microbial biomass did not change significantly as a result of the compaction treatment, but was shown to either decrease or increase over time depending on the methodology used to estimate microbial biomass.     

长期施用生物有机肥对土壤肥力及微生物生物量碳的影响

为了研究施用生物有机肥(EM堆肥,即有效微生物制剂 堆肥)对土壤肥力及微生物生物量碳的影响,进行了7年的施用15t/hm2.a有机肥、施用7.5t/hm2.a有机肥(包括EM堆肥、EM鸡粪肥和传统有机肥)、施用化肥和对照处理的田间试验。结果表明:长期施用生物有机肥的土壤肥力明显提高。随着生物有机肥用量的提高,碱性土壤的pH值逐渐降低,土壤有机质、全N、碱解氮、有效磷、速效钾、微生物生物量碳含量增加,与有机肥施用量呈显著正相关。施用化肥可一定程度提高土壤有机质、全N和有效养分含量,但作用不明显。施肥对土壤肥力和微生物量碳的影响趋势是:EM堆肥>传统堆肥>化肥>对照。土壤微生物量碳与土壤有机质、全N、碱解氮、有效磷、速效钾含量呈显著正相关,可以作为施肥过程中土壤质量变化的生物学指标。     

Long-term effects of tillage and fallow-frequency on soil quality attributes in a clay soil in semiarid southwestern saskatchewan

Reduced tillage management is being adopted at an accelerated rate on the Canadian prairies. This may influence soil quality and productivity. A study conducted on a clay soil (Udic Haplustert) in southwestern Saskatchewan, Canada, to determine the effects of fallow frequency [fallow-wheat (F-W) vs. continuous wheat (Cont W)] and tillage [no-tillage (NT) vs. conventional (CT) or minimum tillage (MT)] on yields of spring wheat (Triticum aestivum L.), was sampled after 3, 7 and 11 years to assess changes in selected soil quality attributes. Tillage had no effect on amount of crop residues returned to the land, but the tilled systems had significantly (P<0.05) lower total organic C and N in the 0–7.5 cm soil depth, though not in the 7.5–15 cm depth. Further, these differences were observed after only 3 years and persisted for the entire 11 years of the study. For example, in the 0–7.5 cm depth, organic C in F-W (MT) after 3 years was 10 480 kg ha⁻¹ and in F-W (NT) 13 380 kg ha⁻¹, while in Cont W (CT) and Cont W (NT) corresponding values were 11 310 and 13 400 kg ha⁻¹, respectively. After 11 years, values for F-W (MT) and F-W (NT) were 11 440 and 14 960 kg ha⁻¹, respectively, and for Cont W (CT) and Cont W (NT), 12 970 and 16 140 kg ha⁻¹, respectively. In contrast to total organic matter, two of the more labile soil quality attributes [i.e., C mineralization (C_min) and N mineralization (N_min)] did not respond to fallow frequency until after 7 years and only in the 0–7.5 cm depth. Microbial biomass (MB) and the ratio of C_min to MB [specific respiratory activity (SRA)], two attributes also regarded as labile, were not influenced by the treatments even after 11 years. After 11 years, only C_min and N_min among the labile soil quality attributes responded to the treatments. Surprisingly, the labile attributes were no more sensitive to the treatments than was total organic C or N. More research is required to determine why responses in this soil differed from those reported elsewhere.     

Substrate inputs and pH as factors controlling microbial biomass, activity and community structure in an arable soil

Our aim was to determine whether the smaller biomasses generally found in low pH compared to high pH arable soils under similar management are due principally to the decreased inputs of substrate or whether some factor(s) associated with pH are also important. This was tested in a soil incubation experiment using wheat straw as substrate and soils of different pHs (8.09, 6.61, 4.65 and 4.17). Microbial biomass ninhydrin-N, and microbial community structure evaluated by phospholipid fatty acids (PLFAs), were measured at 0 (control soil only), 5, 25 and 50 days and CO₂ evolution up to 100 days. Straw addition increased biomass ninhydrin-N, CO₂ evolution and total PLFA concentrations at all soil pH values. The positive effect of straw addition on biomass ninhydrin-N was less in soils of pH 4.17 and 4.65. Similarly total PLFA concentrations were smallest at the lowest pH. This indicated that there is a direct pH effect as well as effects related to different substrate availabilities on microbial biomass and community structure. In the control soils, the fatty acids 16:1ω5, 16:1ω7c, 18:1ω7c&9t and i17:0 had significant and positive linear relationships with soil pH. In contrast, the fatty acids i15:0, a15:0, i16:0 and br17:0, 16:02OH, 18:2ω6,9, 17:0, 19:0, 17:0c9,10 and 19:0c9,10 were greatest in control soils at the lowest pHs. In soils given straw, the fatty acids 16:1ω5, 16:1ω7c, 15:0 and 18:0 had significant and positive linear relationships with pH, but the concentration of the monounsaturated 18:1ω9 PLFA decreased at the highest pHs. The PLFA profiles indicative of Gram-positive bacteria were more abundant than Gram-negative ones at the lowest pH in control soils, but in soils given straw these trends were reversed. In contrast, straw addition changed the microbial community structures least at pH 6.61. The ratio: [fungal PLFA 18:2w6,9]/[total PLFAs indicative of bacteria] indicated that fungal PLFAs were more dominant in the microbial communities of the lowest pH soil. In summary, this work shows that soil pH has marked effects on microbial biomass, community structure, and response to substrate addition.     

长期平衡施肥对潮土微生物活性和玉米养分吸收的影响

利用中国科学院封丘农业生态实验站农田生态系统养分平衡长期定位试验地,研究氮磷钾平衡施肥(NPK)与缺素施肥(NK、PK、NP)对土壤微生物生物量、酶活性、呼吸强度以及玉米养分吸收的影响。结果发现,与不施肥对照(CK)相比,NPK处理玉米根系与茎叶生物量、籽粒产量以及植株氮磷钾吸收量均大幅提高,NP处理次之,PK与NK处理则无显著影响;同一处理玉米茎叶与根系养分含量接近,而籽粒的全氮和全磷含量较高、全钾含量偏低;与NPK处理相比,缺施氮、磷或钾肥均直接导致玉米植株相应养分的明显亏缺或其他养分的过量富集,但在根系、茎叶和籽粒部位的累积情况存在一定差异。与CK相比,所有施加磷肥的处理(NPK、NP、PK)土壤微生物生物量(碳、氮、磷)、脱氢酶、转化酶、脲酶与碱性磷酸酶活性以及土壤微生物代谢活性和土壤基础呼吸强度均显著升高(p<0.05),土壤微生物代谢熵则显著下降(p<0.05),而缺施磷肥的NK处理除显著提高脲酶活性外(p<0.05),对其他指标均无显著影响。结果表明,氮磷钾平衡施肥在促进土壤微生物繁育和保育微生物代谢活性以及促进作物生长和保证养分吸收等方面显得非常重要,而缺素施肥中以缺施磷肥的不利影响最为突出。     

培肥措施培肥土壤的效果与机理研究进展

土壤肥力是农业可持续发展的基础资源,培肥是维持农业土壤肥力水平最主要的措施之一,藉以补偿由于养分随农产品收获及农作物废弃物(如秸秆)带出农田对土壤养分库亏损造成的影响。如何对农田土壤进行有效培肥,达到既提高作物产量和品质,又使农田土壤保持较高肥力,同时有效控制农业面源污染,维护农田良好生态环境,已成为目前农业现代化面临的重要课题之一。本文综述了国内外有关培肥措施与土壤肥力水平关系的研究进展,重点阐述了培肥措施与土壤基本理化性状、土壤酶活性、土壤微生物肥力指标、土壤动物肥力指标之间关系的规律,并指出培肥措施与土壤肥力关系方面今后的研究重点,主要包括:有机肥的精细化高效化投入与土壤肥力关系研究、土壤动物学肥力指标的深入研究、土壤长期培肥的土壤生物学过程研究、土壤培肥与农业面源污染问题研究。本文旨在为通过合理培肥措施来提高农田土壤肥力及维护农田良好生态环境方面的深入研究提供科学依据。     

不同有机物料培肥对渭北旱塬土壤微生物学特性及土壤肥力的影响

通过田间试验,研究了施用不同有机物料对渭北旱塬耕地土壤微生物学特性及土壤肥力的影响。结果表明,化肥与不同有机物料配合施用,土壤微生物学特性［微生物量碳（MBC）、微生物量氮（MBN）、脲酶、碱性磷酸酶］以及部分土壤养分状况（全氮、速效磷、速效钾、阳离子交换量）比单施化肥处理均得到进一步改善。化肥配施秸秆堆肥处理效果最明显,其中微生物量碳增加了41.96%,微生物量氮增加了54.55%,脲酶活性增加了19.71%,碱性磷酸酶活性增加了7.35%,速效磷增加了63.12%;而且土壤微生物量碳、氮与速效磷、阳离子交换量呈显著正相关,微生物商（qMB）、脲酶活性、碱性磷酸酶活性与全氮、速效氮、速效钾含量呈显著相关;同时SMBC、SMBN、qMB等与作物产量密切相关（相关系数分别为0.85,0.74,0.82）。因此,化肥配施秸秆堆肥处理在渭北旱地雨热条件下对于全面提升土壤质量具有重要的意义;同时该区域土壤中微生物量碳氮与土壤养分状况、作物产量具有很好的一致性,可以表征土壤肥力状况及生产力水平。     

Microbiological parameters as indicators of soil quality under various soil management and crop rotation systems in southern Brazil

The objective of this work was to identify soil parameters potentially useful to monitor soil quality under different soil management and crop rotation systems. Microbiological and chemical parameters were evaluated in a field experiment in the State of Paraná, southern Brazil, in response to soil management [no-tillage (NT) and conventional tillage (CT)] and crop rotation [including grain (soybean, S; maize, M; wheat, W) and legume (lupin, L.) and non-legume (oat, O) covers] systems. Three crop rotation systems were evaluated: (1) (O/M/O/S/W/S/L/M/O/S), (2) (O/S/L/M/O/S/W/S/L/M), and (3) (O/S/W/S/L/M/O/M/W/M), and soil parameters were monitored after the fifth year. Before ploughing, CO₂-emission rates were similar in NT and CT soils, but plough increased it by an average of 57%. Carbon dioxide emission was 13% higher with lupin residues than with wheat straw; decomposition rates were rapid with both soil management systems. Amounts of microbial biomass carbon and nitrogen (MB-C and MB-N, respectively) were 80 and 104% higher in NT than in CT, respectively; however, in general these parameters were not affected by crop rotation. Efficiency of the microbial community was significantly higher in NT: metabolic quotient (qCO₂) was 55% lower than in CT. Soluble C and N levels were 37 and 24% greater in NT than in CT, respectively, with no effects of crop rotation. Furthermore, ratios of soluble C and N contents to MB-C and MB-N were consistently lower in NT, indicating higher immobilization of C and N per unit of MB. The decrease in qCO₂ and the increase in MB-C under NT allowed enhancements in soil C stocks, such that in the 0–40 cm profile, a gain of 2500 kg of C ha⁻¹ was observed in relation to CT. Carbon stocks also varied with crop rotation, with net changes at 0–40 cm of 726, 1167 and −394 kg C ha⁻¹ year, in rotations 1, 2 and 3, respectively. Similar results were obtained for the N stocks, with 410 kg N ha⁻¹ gained in NT, while crop rotations 1, 2 and 3 accumulated 71, 137 and 37 kg of N ha⁻¹ year⁻¹, respectively. On average, microbial biomass corresponded to 2.4 and 1.7% of the total soil C, and 5.2 and 3.2% of the N in NT and CT systems, respectively. Soil management was the main factor affecting soil C and N levels, but enhancement also resulted from the ratios of legumes and non-legumes in the rotations. The results emphasize the importance of microorganisms as reservoirs of C and N in tropical soils. Furthermore, the parameters associated with microbiological activity were more responsive to soil management and crop rotation effects than were total stocks of C and N, demonstrating their usefulness as indicators of soil quality in the tropics.     

A rapid procedure for estimating nitrogen mineralization in manured soil

 A routine soil testing procedure for soil N mineralization is needed that is rapid and precise. Not accounting for N mineralization can result in the over-application of N, especially in soils with a history of manure application. Our objectives were to compare results from a recently proposed rapid laboratory procedure with: (1) long-term N mineralization under standard laboratory conditions, and (2) actual forage N uptake from soil receiving dairy cattle (Bos taurus) manure in a 2-year field study. The rapid procedure is based on the quantity of CO₂-C evolved during 24 h under optimum laboratory conditions following the rewetting of dried soil. Dairy cattle manure was surface applied beginning in 1992 at annual rates of 0, 112, 224, or 448 kg N ha^–1 to field plots on a Windthorst fine sandy loam soil (fine, mixed, thermic Udic Paleustalf) near Stephenville, Texas (32°N, 98°W). Results of the one-day CO₂ procedure were highly correlated with soil N mineralized from samples collected in March of 1995 (P=0.004) and 1996 (P<0.001) and with forage N uptake (P<0.001) both years of the study. Residual inorganic N in the same soil samples was poorly correlated with soil N mineralization and forage N uptake. Received: 23 February 2000     

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.     

Substrate quality affects microbial‐ and enzyme activities in rooted soil

The rhizosphere reflects a sphere of high substrate input by means of rhizodeposits. Active microorganisms and extracellular enzymes are known to be responsible for substrate utilization in soil, especially in rooted soil. We tested for microbial‐ and enzyme activities in arable soil, in order to investigate the effects of continuous input of easily available organics (e.g., root‐exudates) to the microbial community. In a field experiment with maize, rooted and root‐free soil were analyzed and rhizosphere processes were linked to microbial activity indicators such as specific microbial growth rates and kinetics of six hydrolytic extracellular enzymes: β‐glucosidase, β‐cellobiohydrolase, β‐xylosidase, acid phosphatase, leucine‐ and tyrosine‐aminopeptidase. Higher potential activities of leucine‐aminopeptidase (2‐fold) for rooted vs. root‐free soil suggested increased costs of enzyme production, which retarded the specific microbial growth rates. Total microbial biomass determined by the substrate‐induced respiration technique and dsDNA extraction method was 23% and 42% higher in the rooted surface‐layer (0–10 cm) compared to the root‐free soil, respectively. For the rooted soil, potential enzyme activities of β‐glucosidase were reduced by 23% and acid phosphatase by 25%, and increased by 300% for β‐cellobiohydrolase at 10–20 cm depth compared to the surface‐layer. The actively growing microbial biomass increased by the 17‐fold in rooted soil in the 10–20 cm layer compared to the upper 10 cm. Despite the specific microbial growth rates showing no changes in the presence of roots, these rates decreased by 42% at 10–20 cm depth compared to the surface‐layer. This suggests the dominance in abundances of highly active but slower growing microbes with depth, reflecting also their slower turnover. Shifts in microbial growth strategy, upregulation of enzyme production and increased microbial respiration indicate strong root effects in maize planted soil.     

Application of multiple regression and neural network approaches for landscape-scale assessment of soil microbial biomass

Previous soil surveys across the north-east German lowland have reported significant correlations of soil microbial biomass (SMB) contents and organic carbon and total nitrogen contents as well as texture. Using these data sets obtained from 89 arable sites along a regional-scale transect, a linear full-factorial regression model and a neural network model were constructed and evaluated for landscape-scale assessment of SMB. The validation by means of an additional data set consisting of 30 long-term soil observation sites located in the federal state of Brandenburg was within a confidence range of 95%. Using existing models from other regions with our data sets resulted in underestimation of SMB, while using data sets from another region with our model led to overestimation of SMB. It was concluded that a linear full-factorial regression model approach, as well as neural network modelling are promising tools for the prediction of SMB at the landscape scale but need to be validated for the respective region.     

Three decades of soil microbial biomass studies in Brazilian ecosystems: Lessons learned about soil quality and indications for improving sustainability

Soil microbial biomass plays important roles in nutrient cycling, plant-pathogen suppression, decomposition of residues and degradation of pollutants; therefore, it is often regarded as a good indicator of soil quality. We reviewed more than a hundred studies in which microbial biomass-C (MB-C), microbial quotient (MB-C/TSOC, total soil organic carbon) and metabolic quotient (qCO₂) were evaluated with the objective of understanding MB-C responses to various soil-management practices in Brazilian ecosystems. These practices included tillage systems, crop rotations, pastures, organic farming, inputs of industrial residues and urban sewage sludge, applications of agrochemicals and burning. With a meta-analysis of 233 data points, we confirmed the benefits of no-tillage in preserving MB-C and reducing qCO₂ in comparison to conventional tillage. A large number of studies described increases in MB-C and MB-C/TSOC due to permanent organic farming, also benefits from crop rotations particularly with several species involved, whereas application of agrochemicals and burning severely disturbed soil microbial communities. The MB-C decreased in overgrazed pastures, but increased in pastures rotated with well-managed crops. Responses of MB-C, MB-C/TSOC and qCO₂ to amendment with organic industrial residues varied with residue type, dose applied and soil texture. In conclusion, MB-C and related parameters were, indeed, useful indicators of soil quality in various Brazilian ecosystems. However, direct relationships between MB-C and nutrient-cycling dynamics, microbial diversity and functionality are still unclear. Further studies are needed to develop strategies to maximize beneficial effects of microbial communities on soil fertility and crop productivity.     

Altering soil carbon and nitrogen stocks in intensively tilled two-year rotations

Information is needed on the ability of different crop management factors to maintain or increase soil C and N pools, especially in intensively tilled short crop rotations. Soil samples from field experiments in Maine were used to assess the effect of cover crop, green manure (GM) crop, and intermittent or annual amendment on soil C and N pools. These field experiments, of 6–13 years duration, were all characterized by a 2-year rotation with either sweet corn ( Zea mays L.) or potato ( Solanum tuberosum L.), and primary tillage each year. Total, particulate organic matter (POM), and soil microbial biomass (SMB)-C and -N pools were assessed for each experiment. Total C and N stocks were not affected by red clover ( Trifolium pratense L.) cover crop or legume GM, but were increased by 25–53% via a single application of papermill sludge or an annual manure and/or compost amendment. With the exception of continuous potato production which dramatically reduced the SMB-C and SMB-N concentration, SMB-C and -N were minimally affected by changes in cropping sequence, but were quite sensitive to amendments, even those that were primarily C. POM-C and -N, associated with the coarse mineral fraction (53–2,000 µm), were more responsive to management factors compared to total C and N in soil. The change in soil C fractions was a linear function of increasing C supply, across all experiments and treatments. Within these intensively tilled, 2-year crop rotations, substantial C and N inputs from amendments are needed to significantly alter soil C and N pools, although cropping sequence changes can influence more labile pools responsible for nutrient cycling.     

Effects of soil compaction on N-mineralization and microbial-C and -N. II. Laboratory simulation

Soil compaction can affect the turnover of C and N (e.g. by changing soil aeration or by changing microbial community structure). In order to study this in greater detail, a laboratory experiment simulating total soil porosities representative of field conditions in cropped and pasture soils was set up. Soils were silty clay loams (Typic Endoaquepts) from a site that had been cropped with cereals continuously for 28 years, a permanent pasture and a site that had been cropped with maize continuously for 10 years. Soils from the three sites were compacted into cores to different total porosities (corresponding bulk densities ranging from 0.88 to 1.30 Mg m⁻³). The soil cores were equilibrated to different matric potentials (ranging from −1 to −100 kPa), yielding values for the fraction of air-filled pores of < 0.01 to 0.53 m³ m⁻³, and then incubated at 25°C for 21 days. C-mineralization was on average 15, 33 and 21 μg C g⁻¹ day⁻¹ for soils from the cropped, pasture and maize sites, respectively, and was positively correlated with soil water contents. Net N-mineralization showed a similar pattern only for well-aerated, high total porosity cores (corresponding bulk density 0.88 Mg m⁻³) from the pasture soil. Denitrification at < 0.20 m³ m⁻³ for the fraction of air-filled pores may have caused the low N-mineralization rates observed in treatments with high water content or low porosity. Microbial biomass estimates decreased significantly with increasing water contents if measured by fumigation-extraction, but were not significantly affected by water content if estimated by the substrate-induced respiration method. The degree of soil compaction did not affect the microbial biomass estimates significantly but did affect microbial activity indirectly by altering aeration status.     

福建黄泥田肥力质量特征与最小数据集

黄泥田为福建省主要中低产田类型之一,约占水稻土面积的30%。为解析关键限制因子及开展黄泥田肥力质量评价,进而实施针对性的改良措施,采用配对采样方法,采集福建省20对典型黄泥田与邻近同一微地貌单元内高产灰泥田表层土壤,分析了两种土壤类型28项属性因子指标差异及其原因,并采用主成分分析等方法构建福建省黄泥田肥力质量评价因子最小数据集,通过加权指数法分别计算最小数据集土壤肥力质量指数与差异显著因子构成的重要数据集土壤肥力质量指数。结果表明,与灰泥田相比,黄泥田的有机质含量低19.1%,全氮、全磷、全钾含量分别低14.8%、29.9%和25.4%,碱解氮、有效磷和速效钾含量分别低17.8%、56.7%和39.3%,CEC、交换性钙、交换性镁含量分别低12.9%、50.6%和30.8%,有效铁、有效硼和有效锌含量分别低25.6%、33.3%和44.1%。黄泥田的物理性黏粒、0.001 mm黏粒和容重分别较灰泥田高20.8%、25.6%和12.3%,而孔隙度低19.3%。黄泥田过氧化氢酶活性较灰泥田高20.4%,脲酶活性较灰泥田低40.4%。用主成分分析方法从上述19项有显著差异的因子构成的重要数据集中归纳出累计贡献率达76.22%并能反映黄泥田综合肥力特征的6个主成分,建立了由CEC、全钾、有效磷、有效硼和孔隙度5项因子组成的黄泥田肥力评价最小数据集,相应的黄泥田最小数据集土壤肥力质量指数仅相当于灰泥田的69.5%,通过与重要数据集的土壤肥力质量指数相关分析比较,最小数据集可代替重要数据集对福建省黄泥田土壤肥力质量进行正确评价。     

Different approaches to evaluating soil quality using biochemical properties

Soil biochemical properties are indicators of soil quality, but there is still no consensus as to how they should be used. We review the trends in their use over the last decade. Generally, biochemical properties related to the biocycles of the elements (C, N, P and S) are used to diagnose soil quality. These properties include both general biochemical parameters (i.e. microbial biomass C, dehydrogenase activity and N mineralization potential) and specific biochemical parameters (i.e. the activity of hydrolytic enzymes, such as phosphatase, urease and β-glucosidase). Biochemical properties can be used both individually, as simple indices, or in combination using complex equations derived from mathematical combinations or the application of statistical programs. The results described in the literature for both are contradictory and question the validity of the use of biochemical properties as quality indicators. Complex expressions, in which different properties are combined, are thought to be highly suitable for estimating soil quality, although their use is limited to the area and situation in which they have been described. Generally, the greatest problems posed by the use of biochemical properties as soil quality indicators include the lack of reference values, the contradictory behaviour shown by these properties when a soil is degraded, and the regional variations in expression levels. Most of these problems are derived from the scarce information available on the biochemical properties of soil. For this reason, obtaining soil quality indicators of general use will require a coordinated effort from the international scientific community to standardise the analytical methods and to compile databases of biochemical properties from soils under diverse geographic conditions and with different uses and management.     

土壤微生物量碳周转分析方法及其影响因素

简述了目前国内外常用的3种测定土壤微生物生物量C周转分析方法及其影响因素、改进的土壤微生物生物量C周转动力学测定方法及其应用前景,并分析了国内外不同生态环境、土壤质地和耕作管理制度等的土壤微生物生物量C周转的研究结果。