Interrelationship of Carbon Sequestration,Soil Fertility,and Microbial Indices as Influenced by Long-Term Land Uses in Lower Himalayan Region,India

The study was conducted to determine the long-term impact of different land uses on carbon sequestration, soil fertility, and microbial indices and to establish their interrelationship in a light-textured hyperthermic Udic Ustochrept. Soil samples were collected from existing land-use systems of (1) Eucalyptus tereticornis, (2) Terminalia chebula, (3) Acacia nilotica, (4) Leucaena leucocephala, (5) Embilica officinalis, (6) Zizyphus spp., and (7) maize–wheat rotation from depths of 0–15, 15–30, and 30–45 cm and examined for pH; organic carbon (OC); electrical conductivity (EC); available nitrogen (N), phosphorus (P), and potassium (K); micronutrients; microbial biomass carbon (MBC); microbial biomass nitrogen (MBN); and microbial biomass phosphorus (MBP). High-density plantations of Eucalyptus teriticornis had a greater potential in sequestering aboveground carbon (472.37 Mg ha^?1), compared to widely spaced trees of Acacia nilotica (376.05 Mg ha^?1). Eucalyptus teriticornis exhibited the greatest impact in increasing soil OC in all depths, followed by Acaccia nilotica and Terminalia chebula, and the lowest was in agriculture (0.778, 0.749, 0.590, and 0.471%, respectively, in surface soil). Available zinc and iron contents were greatest under Eucalyptus tereticornis, followed by Acacia nilotica, Zizyphus mauritiana, Embilica officinalis, Terminalia chebula, and Leucaena leucocephala. The MBC and MBN were greatest in Eucalyptus tereticornis, followed by Acacia nilotica, and lowest in agriculture. Correlation matrix revealed significant and positive relationships between carbon sequestered with OC, MBC, MBN, and MBP.     

Microbial Properties of a Loess Soil as Affected by Various Nutrient Management Practices in the Loess Plateau of China

Microbial biomass phosphorus (MBP) and its relationships with other biological and chemical properties were studied on loess soil with an 11-year long-term fertilization experiment. The results indicated that inorganic fertilizers (F) improved soil microbial biomass carbon (MBC), nitrogen (MBN), and MBP levels and F plus maize stalk (SNPK) improved MBC and MBN. Manuring markedly increased soil MBC, MBN, and MBP levels. Fertilization decreased the ratios of MBC/MBN, MBC/MBP, and MBN/MBP. Microbial biomass phosphorus was positively and linearly correlated with MBC, MBN, organic carbon (SOC), total phosphorus (TP), water-soluble P, and Olsen P but negatively correlated with soil pH. Microbial biomass phosphorus constituted 2% of TP on control (CK) and inorganic fertilizer treatments and 12% on manure plots. Microbial biomass phosphorus to Olsen P ratios were 50% on CK, F, and SNPK and 80% on manure treatments. Measurements of MBP in soil containing high Olsen P were subject to analytical problems of unknown reasons.     

Nitrogen immobilization/remineralization in legume‐amended soils as influenced by texture and compaction

Abstract

The role of intrinsic soil properties and management induced changes in bulk density on legume shoot biomass‐nitrogen (N) turnover to soil mineral N [nitrate (NO₃) plus ammonium (NH₄)], SMN, through soil microorganisms is poorly understood. In this study, the influence of intrinsic soil properties and changes in bulk density in soils amended with red clover (Trifolium pratense L.) on N immobilization/remineralization was investigated. Time in incubation, soil type, bulk density, and legume amendment had significant influence on the amounts of microbial biomass carbon (C) (MBC), N (MBN), and the SMN measured during incubation. During the first 32 days in incubation, MBC and MBN in the legume‐amended soils were higher than the control whereas an opposite trend existed for SMN. The SMN measured at the end of incubation, i.e., 70 days after incubation, was significantly higher than the unamended control. The ratio of SMN to MBN (SMN:MBN) was < 1.0, in general, during the first 32 days in incubation in legume amended soils, indicating N immobilization in microbial biomass during this period. Forty‐two days after incubation, the SMN:MBN ratios in the legume amended soils were >1.0, indicating remineralization of the immobilized N, derived, at least partially, from the legume. In the unamended control, these ratios were > 1.0 throughout the incubation. Over time, 63% to 76% of the variability in N‐immobilization/remineralization (SMN:MBN) was accounted for clay content, water (WFP) and air (AFP) filled porosities, volume fraction of pores (VFP) <1.5 μm, total N, C to N ratios in soils, bulk density, and legume amendment. The results indicate the influence of intrinsic soil properties and bulk density on microbially mediated legume N turnover to SMN changed over time.     

Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.     

Responses of microbial biomass and respiration of soil to topography,burning, and nitrogen fertilization in a temperate steppe

Temporal dynamics of microbial biomass and respiration of soil and their responses to topography, burning, N fertilization, and their interactions were determined in a temperate steppe in northern China. Soil microbial indices showed strong temporal variability over the growing season. Soil microbial biomass C (MBC) and N (MBN) were 14.8 and 11.5% greater in the lower than upper slope, respectively. However, the percentage of organic C present as MBC and the percentage of total N present as MBN were 16.9 and 26.2% higher in the upper than lower slope, respectively. Neither microbial respiration (MR) nor metabolic quotient (qCO₂) was affected by topography. Both MBC and MBN were increased by burning, on average, by 29.8 and 14.2% over the growing season, and MR and qCO₂ tended to reduce depending on the sampling date, especially in August. Burning stimulated the percentage of organic C present as MBC and the percentage of total N present as MBN in the upper slope, but did not change these two parameters in the lower slope. No effects of N fertilization on soil microbial indices were observed in the first growing season after the treatment. Further research is needed to study the long-term relationships between changes in soil microbial diversity and activity and plant community in response to burning and N fertilization.     

长期免耕与施用有机肥对土壤微生物生物量碳、氮、磷的影响

通过设置在江苏省句容农科所的田间定位试验研究长期免耕及施用有机肥料对土壤微生物生物量碳、氮、磷的影响。结果表明 :经过 1 6年 32茬稻—麦水旱轮作后 ,表土层 ( 0～ 5cm)土壤微生物生物量碳、氮、磷含量比亚表层 ( 5～ 1 0cm)分别高 2 7.5 %、43.6%和1 1 %。与常规耕翻相比长期免耕处理表土层土壤微生物生物量碳、氮含量分别增加了2 5 .4%和 45 .4% ,而微生物生物量磷无明显变化规律 ;亚表层的土壤微生物生物量碳、氮、磷免耕与耕翻两种耕作方式间的差异不显著。尽管各施肥处理施用的氮、磷、钾数量完全相等 ,但土壤微生物生物量碳、氮、磷的含量却因肥料种类的不同而异。综合 0～ 5和 5～ 1 0cm土层 ,微生物生物量碳、磷为 :猪粪 化肥 >秸秆 化肥 >绿肥 化肥 >化肥 >不施肥 ,微生物生物量氮则为 :猪粪 化肥 >绿肥 化肥 >秸秆 化肥 >化肥 >不施肥。相关分析结果显示 ,土壤微生物生物量碳、氮与土壤有机碳、土壤全氮和土壤碱解氮之间均呈极显著的正相关 ,表明其与土壤肥力关系密切 ,可作为评价土壤肥力性状的生物学指标     

除草剂和土壤改良剂对热带农业生态系统中微生物生物量动态的影响

The influences of herbicide alone and in combination with the soil amendments with contrasting resource qualities on dynamics of soil microbial biomass C (MBC), N (MBN), and P (MBP) were studied through two annual cycles in rice-wheat-summer fallow crop sequence in a tropical dryland agroecosystem. The experiment included application of herbicide (butachlor) alone or in combination with various soil amendments having equivalent amount of N in the forms of chemical fertilizer, wheat straw, Sesbania aculeata, and farm yard manure (FYM). Soil microbial biomass showed distinct temporal variations in both crop cycles, decreased from vegetative to grain-forming stage, and then increased to maximum at crop maturity stage. Soil MBC was the highest in herbicide + Sesbania aculeata treatment followed by herbicide + FYM, herbicide + wheat straw, herbicide + chemical fertilizer, and herbicide alone treatments in decreasing order during the rice-growing period. During wheat-growing period and summer fallow, soil MBC attained maximum for herbicide + wheat straw treatment whereas herbicide + FYM, herbicide + Sesbania, and herbicide + chemical fertilizer treatments showed similar levels. The overall trend of soil MBN was similar to those of soil MBC and MBP except that soil MBN was higher in herbicide + chemical fertilizer treatment over the herbicide + wheat straw treatment during rice-growing period. In spite of the addition of equivalent amount of N through exogenous soil amendments in combination with the herbicide, soil microbial biomass responded differentially to the treatments. The resource quality of the amendments had more pronounced impact on the dynamics of soil microbial biomass, which may have implications for long-term sustainability of rainfed agroecosystems in dry tropics.     

Nitrogen addition and mowing affect microbial nitrogen transformations in a C4 grassland in northern China

Microbial nitrogen (N) transformations play a key role in regulating N cycling in grassland ecosystems. However, there is still little information on how management of semi‐arid grassland such as mowing and/or N fertilizer application affects microbial activity and N transformations. In a field experiment in northern China, N was added at a rate of 10 g N m^?2 year^?1 as NH₄NO₃ to mown and unmown plots (4 × 4 m²) and in situ rates of net ammonification (R_amm), nitrification (R_nit) and mineralization (R_min) were followed at monthly intervals for the vegetation growth periods in the years 2006–2009. In addition, we also measured soil microbial biomass carbon (MBC) and nitrogen (MBN), microbial respiration (MR) and peak above‐ground biomass in August of each measurement year. Driven by the pronounced inter‐annual variability of rainfall, all the properties investigated varied markedly across years. Nevertheless, we were able to demonstrate that over the 4 years N addition significantly stimulated R_nit, R_min and MBN, on average, by 288, 149 and 11.6%, respectively. However, N addition decreased MBC significantly as well as the ratio of MBC:MBN by, on average, 10 and 23%, respectively, whereas an effect of N addition on MR could not be demonstrated. Mowing decreased MBN, MR and qCO₂ significantly by 9, 28 and 24%, respectively, but no effects were found on microbial net N transformation rates and MBC. N addition and mowing interactively affected R_amm and R_min, and MBN, MBC:MBN. In summary, our results indicate a positive effect of N addition but a negative effect of mowing on microbial N transformation in this C4 grassland in northern China.     

The microbial biomass and activity in soil with shrub (Caragana korshinskii K.) plantation in the semi-arid loess plateau in China

Caragana korshinskii K. is a shrub species which is adapted to arid and semi-arid environments and plays an important role in soil protection. The objective of this study was to determine the influence of this shrub plantation on the soil ecosystem functions driven by microorganisms in the long-term. The changes in the size and activity of soil microbial biomass and the relationship between soil microbial biomass and chemical properties were investigated under shrub plantations aged 6, 18 and 26 years. The results showed that the pH value in the soil decreased gradually, while soil organic carbon (OC) and total nitrogen (TN) significantly increased with the age of C. korshinskii. Although microbial biomass carbon (MBC) and MBC/OC ratio gradually increased, the ratio of basal respiration to MBC (qCO₂) decreased with the age of C. korshinskii. The microbial biomass nitrogen (MBN) and MBC had a positive relationship with soil TN and OC, respectively. The flux of CO₂ decreased with the age of C. korshinskii which had a significant negative relationship with soil OC, TN, MBN and MBC. The results indicate that C. korshinskii plantations may help to improve microbially driven ecosystem functioning through long-term creation of resource-island.     

喀斯特峰丛洼地不同植被类型土壤微生物量碳氮磷和养分特征

  目的  探讨桂西北喀斯特峰丛洼地不同植被类型的土壤理化性质和微生物碳(MBC)、微生物氮（MBN）、微生物磷（MBP）含量的变化特征及它们之间的关系。  方法  利用生态化学计量方法和Pearson相关性分析方法研究不同植被类型和土层深度对土壤MBC、MBN、MBP含量和土壤养分含量分布特征的影响。  结果  （1）不同植被类型土壤养分含量和MBC、MBN、MBP含量依次为次生林 > 灌木 > 灌草 > 草地 > 耕地;土壤养分垂直分布表现为随着土层深度加深而下降,不同土层间土壤有机碳（SOC）、全氮（TN）、全磷（TP）含量差异显著,土壤MBC、MBN和MBP含量在不同植被类型和不同土层间差异显著,均表现为MBC > MBN > MBP。（2）不同植被类型土壤MBC/SOC和MBP/TP的值较小,MBN/TN的差异较大。不同植被类型的土壤MBC/MBN差异显著,MBC/MBP变化范围较大,MBN/MBP表现为次生林 > 灌草 > 灌木 > 草地 > 耕地。（3）土壤MBC和MBN与SOC、TN、速效氮和速效钾呈显著或极显著正相关,与土壤容重、pH值表现出不同程度的负相关,表明植被恢复过程中土壤MBC和MBN可作为衡量土壤养分的敏感性指标。  结论  不同植被类型的土壤微生物生物量碳氮磷、养分含量和化学计量特征有明显的表聚效应,随着植被的正向演替,土壤结构、养分和微生物群落功能得到显著提高。     

Temporal changes in fertility and microbial properties of soil in forest-converted oil palm plantations in Okomu forest reserve,Nigeria

Evidence of the impacts of land-use change on soil biological activities, a determinant of nutrient cycling in soil, will provide a better understanding of soil health and productivity. The study investigates temporal changes in soil chemical and microbial properties in a forest converted to oil palm plantation. Soil samples from four locations: native forest and Elaeis guineensis plantations of 2-, 13- and 14-year were collected. Total carbon C and N were significantly higher (p < 0.05) in the native forest (NF) followed by 14- and 13-year E. guineensis plantations respectively. Microbial biomass carbon (MBC) and nitrogen (MBN) in NF were significantly higher (p < 0.05) than in the E. guineensis plantations. There were no significant differences in the microbial biomass phosphorus (MBP) among the E. guineensis plantation of all ages. The qCO₂ in the 13- and 14-year E. guineensis plantations was higher than in NF and 2-year E. guineensis plantation. There was a positive correlation between MBC, MBN, MBP and pH, P, TC, and TN. These results indicated that conversion of native forest to E. guineensis plantation affected soil nutrient and microbial properties. And there could be a return to healthy soil condition as age of E. guineensis plantation increased.     

Long‐term effects of leguminous cover crops on microbial indices and their relationships in soils of a coconut plantation of a humid tropical region

In this study, leguminous crops like Atylosia scarabaeoides, Centrosema pubescens, Calopogonium mucunoides, and Pueraria phaseoloides. grown as soil cover individually in the interspaces of a 19‐yr‐old coconut plantation in S. Andaman (India) were assessed for their influence on various microbial indices (microbial biomass C, biomass N, basal respiration, ergosterol, levels of ATP, AMP, ADP) in soils (0–50 cm) collected from these plots after 10 years. The effects of these cover crops on . CO₂ (metabolic quotient), adenylate energy charge (AEC), and the ratios of various soil microbial properties viz., biomass C : soil organic C, biomass C : N, biomass N : total N, ergosterol : biomass C, and ATP : biomass C were also examined. Cover cropping markedly enhanced the levels of organic matter and microbial activity in soils after the 10‐yr‐period. Microbial biomass C and N, basal respiration, . CO₂, ergosterol and levels of ATP, AMP, ADP in the cover‐cropped plots significantly exceeded the corresponding values in the control plot. While the biomass C : N ratio tended to decrease, the ratios of biomass N : total N, ergosterol : biomass C, and ATP : biomass C increased significantly due to cover cropping. Greater ergosterol : biomass C ratio in the cover‐cropped plots indicated a decomposition pathway dominated by fungi, and high . CO₂ levels in these plots indicated a decrease in substrate use efficiency probably due to the dominance of fungi. The AEC levels ranged from 0.80 to 0.83 in the cover‐cropped plots, thereby reflecting greater microbial proliferation and activity. The ratios of various microbial and chemical properties could be assigned to three different factors by principal components analysis. The first factor (PC1) with strong loadings of ATP : biomass C ratio, AEC, and . CO₂ reflected the specific metabolic activity of soil microbes. The ratios of ergosterol : biomass C, soil organic C : total N, and biomass N : total N formed the second factor (PC2) indicating a decomposition pathway dominated by fungi. The biomass C : N and biomass C : soil organic C ratios formed the third principal component (PC3), reflecting soil organic matter availability in relation to nutrient availability. Overall, the study suggested that Pueraria phaseoloides. or Atylosia scarabaeoides were better suited as cover crops for the humid tropics due to their positive contribution to soil organic C, N, and microbial activity.     

Response of soil microbial community and diversity to increasing water salinity and nitrogen fertilization rate in an arid soil

The scarcity of fresh water has forced farmers to use saline water (SW) for irrigation. It is important to understand the response of the soil microbial community and diversity to saline irrigation water. The objective of this study was to determine the effects of irrigation water salinity and nitrogen fertilization rates on soil physicochemical properties, microbial activity, microbial biomass, and microbial functional diversity. The field experiment consisted of a factorial design with three levels of irrigation water salinity (electrical conductivities (ECs) of 0.35, 4.61 or 8.04?dS?m^?1) and two nitrogen rates (0 and 360?kg?N?ha^?1). The results showed that the 4.61 and 8.04?dS?m^?1 treatments both reduced soil microbial biomass C (MBC), microbial biomass N (MBN), basal respiration, total phospholipid fatty acid (PLFA), bacterial PLFA, fungal PLFA, and fungal:bacterial ratios. In contrast, the SW treatments increased the MBC:MBN ratio. Nitrogen fertilization increased soil MBC, MBN, basal respiration, total PLFA, bacterial PLFA, and gram-negative bacterial PLFA. In contrast, N fertilization decreased gram-positive bacterial PLFA, fungal PLFA, and fungal:bacterial ratios. Average well color development, Richness, and Shannon's Index were always lowest in the 8.04?dS?m^?1 treatment. Carbon utilization patterns in the 8.04?dS?m^?1 treatment were different from those in the 0.35?dS?m^?1 treatment. In conclusion, five years of irrigation with brackish or SW reduced the soil microbial biomass, activity, and functional diversity, which may cause the deterioration of soil quality. Thus, the high-salinity water (EC?>?4.61?dS?m^?1) is not appropriate as a single irrigation water resource. Proper N fertilizer input may overcome some of the negative effects of salinity on soil microbial.     

除草剂和土壤改良剂对热带农业生态系统中微生物生物量动态的影响（英文）

The influences of herbicide alone and in combination with the soil amendments with contrasting resource qualities on dynamics of soil microbial biomass C(MBC),N(MBN),and P(MBP) were studied through two annual cycles in rice-wheat-summer fallow crop sequence in a tropical dryland agroecosystem.The experiment included application of herbicide(butachlor) alone or in combination with various soil amendments having equivalent amount of N in the forms of chemical fertilizer,wheat straw,Sesbania aculeata,and farm yard manure(FYM).Soil microbial biomass showed distinct temporal variations in both crop cycles,decreased from vegetative to grain-forming stage,and then increased to maximum at crop maturity stage.Soil MBC was the highest in herbicide + Sesbania aculeata treatment followed by herbicide 4- FYM,herbicide + wheat straw,herbicide + chemical fertilizer,and herbicide alone treatments in decreasing order during the rice-growing period.During wheat-growing period and summer fallow,soil MBC attained maximum for herbicide + wheat straw treatment whereas herbicide + FYM,herbicide 4- Sesbania,and herbicide 4 chemical fertilizer treatments showed similar levels.The overall trend of soil MBN was similar to those of soil MBC and MBP except that soil MBN was higher in herbicide 4 chemical fertilizer treatment over the herbicide + wheat straw treatment during rice-growing period.In spite of the addition of equivalent amount of N through exogenous soil amendments in combination with the herbicide,soil microbial biomass responded differentially to the treatments.The resource quality of the amendments had more pronounced impact on the dynamics of soil microbial biomass,which may have implications for long-term sustainability of rainfed agroecosystems in dry tropics.     

Seasonal changes in the microbial biomass of Brazilian soils with different organic matter contents

Abstract

Carbon and nitrogen levels of microbial biomass were studied in four plots located in Rio de Janeiro State, Brazil. Two samplings were carried out, the first one, on November 1992 when rainfall was high which led the soil to high levels of moisture, and the second one on March 1993 when there was a decrease in rainfall coupled with high temperatures. Microbial carbon (MBC) and microbial nitrogen (MBN) assessments were done by the fumigation‐extraction method. The results showed significant differences for MBC and MBN between the sampling times and between different plots. Moreover, MBN showed differences as a function of sampling depth. In the 1993 sampling, developed under moisture conditions of soil which promoted the mineralization of organic matter, lesser values of MBC and MBN were found, whereas there was no difference in the organic carbon content. This fact shows a major sensitivity of biomass measurements to reflect changes which occur in the soil organic matter content. Significant correlations were obtained between MBC and organic carbon (r = 0.35, P < 0.01, n = 68), MBN and total N (r = 0.62; P < 0.07, n = 47), and MBC with NBM (r 0.74, P < 0.01, n = 54).     

不同耕作方式对土壤有机碳、微生物量及酶活性的影响

【目的】依托8年长期(2005~2012)固定道定位试验,研究不同耕作方式对土壤有机碳、土壤微生物量、土壤酶活性在0—90 cm土层的分布特征,为优化中国西北干旱区的耕作方式提供理论依据。【方法】试验包括固定道垄作(PRB)、固定道平作(PFT)与传统耕作(CT)三种耕作模式下的土壤有机碳土壤总有机碳(TOC)、颗粒有机碳(POC)、土壤微生物量碳(MBC)、土壤微生物量氮(MBN)、土壤微生物量磷(MBP)、蔗糖酶、过氧化氢酶、脲酶及小麦产量进行了测定和分析。【结果】在0—90 cm土层,不同耕作方式下的TOC、POC、MBC、MBN、MBP、蔗糖酶活性、脲酶活性均随着土层的增加呈下降趋势,过氧化氢酶活性呈先下降后增大的分布特征;在0—60 cm,固定道保护性耕作能够显著增加心土层作物生长带土壤有机碳储量,有机碳储量大小为PRBPFTCT;PRB、PFT较CT可以显著增加0—10 cm作物生长带TOC、POC、MBC、MBN、MBP含量、蔗糖酶、脲酶活性,其大小为PRBPFTCT;耕作方式对过氧化氢酶活性影响不显著;TOC、POC、MBC、MBN、MBP、蔗糖酶活性、脲酶活性、过氧化氢酶活性之间均达到了显著或极显著相关。【结论】PRB较PFT、CT能够提高耕作层(0—10 cm)土壤有机碳含量、土壤微生物量、土壤酶活性, 增加作物产量, 增大0—60 cm土层有机碳储量,耕作方式(PRB、PFT及CT)对10 cm以下土层土壤环境改善作用不明显。     

Responses of soil chemical and microbial indicators to conservational tillage versus traditional tillage in the North China Plain

This study compared the responses of soil chemical and microbial indicators to the conservational tillage (CT) versus traditional tillage (TT) in a Haplic Cambisol in the North China Plain (NCP). These indicators included soil organic C (SOC), soil total N (STN), soil available P (SAP), cation exchange capacity (CEC), exchangeable Ca²⁺ and Mg²⁺, microbial biomass C (MBC), microbial biomass N (MBN), alkaline phosphomonoesterase (AP), β-glucosidase, N-acetyl-β-glucosaminidase (NAG), nitrate reductase (NR), protease, urease and the geometric mean of the assayed enzymes (GMea). Our results showed that almost all investigated parameters, except the contents of CEC, Ca²⁺, Mg²⁺ and the ratios of GMea/MBN and C/N, were significantly higher under the CT (no-till, NT and reduced-till, RT) than those under the TT, whilst the crop yield was not significantly affected by tillage treatments. Principle component analysis (PCA) showed that the first and second component explained 67.2% and 16.6% of the total variation, respectively. The first component was significantly correlated with GMea, MBC, MBN and β-glucosidase, and effectively discriminated soils under the NT or RT from those under the TT. Our results indicated that the 6-year CT improved the quality of the Haplic Cambisol by enhancing its chemical and microbial properties, whilst GMea, MBC, MBN and β-glucosidase were among the most effective indicators for monitoring these improvements.     

Soil Organic Carbon and Nitrogen Fractions under Different Land Uses and Tillage Practices

Many questions have surfaced regarding long-term impacts of land-use and cultivation system on soil carbon (C) sequestration. The experiment was conducted at Ohio Agricultural Research and Development Center. Only minor variations of soil organic carbon (SOC) and nitrogen (N) fractions with depth under plow tillage (PT). The SOC, total nitrogen (TN), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) concentrations were higher under grassland and forestland in the top 0–15 cm depth than arable soils. No-tillage (NT) also increased SOC and N fractions concentrations in the surface soils than PT. Compared to arable, grass and forest could significantly improve proportions of MBC and MBN, and reduce proportions of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). NT and forest also increased the ratio of SOC/TN, MBC/MBN, and DOC/DON. Overall, grass and forest provided more labile C and improved C sequestration than arable. So did NT under arable land-use.     

有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮

土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。     

山核桃集约经营过程中土壤微生物量碳氮的变化

[目的]研究不同集约经营历史山核桃林的土壤微生物量碳氮的演变规律,为山核桃林地土壤管理提供科学依据。[方法]在浙江省临安市分别采集并分析了经营历史为5,10,15,20a的山核桃林土壤样品,并与天然混交林(0a)进行比较。[结果]天然混交林改造为山核桃纯林并经集约经营后,林地土壤微生物量碳(MBC)、微生物量氮(MBN)、MBC/MBN,MBC/SOC均表现出先下降而后上升的趋势,经过10a经营后降到最低水平,与0a相比,0—10cm土层MBC,MBN和MBC/SOC分别降低了52.1%,32.0%和31.0%。经营10a的林地土壤MBC/MBN显著低于前期经营林地,而MBN/TN在经营过程中的差异并不显著。[结论]山核桃集约经营后,林地土壤微生物量碳氮含量显著下降。