非饱和土基坑抗隆起稳定性研究

鉴于基坑周围土体常处于非饱和状态以及挡墙位移多发生绕墙底RB模式转动,首先采用非饱和土双应力状态变量理论推导墙底条形基础单侧滑动的承载力与RB位移模式下墙-土整体下滑时的竖向抗滑力,继而基于极限平衡法提出均布/线性吸力下非饱和土基坑抗隆起安全系数的求解过程,最后对比文献理论解答进行基坑工程实例应用与验证和挡墙位移模式探讨。研究表明:本文基坑抗隆起安全系数能反映土体非饱和特性与挡墙RB位移模式,可自然退化为饱和土结果,并得到文献地基承载力模式解答和极限上限法解答的合理性验证;挡墙RB位移模式下的竖向抗滑力小于静止状态下的,对应的基坑抗隆起安全系数亦然;非饱和土基坑若按忽略非饱和强度特性的饱和土基坑简化计算,得到的基坑抗隆起安全系数偏于保守。

水肥调控对茶树土壤酶及土壤养分的影响

[目的]探究茶树土壤酶活性、土壤养分和茶树地上部分对水肥调控的响应,揭示水肥调控下土壤酶活性和土壤养分的变化规律,可为基肥施用和灌水互作下对土壤理化性质和幼龄茶树生长影响提供理论依据。[方法]采用盆栽实验方法,设置了施肥量和灌水量2个因素。基肥施肥量设C0(0 kg·盆^(-1))、C1(0.05 kg·盆^(-1))、C2(0.1 kg·盆^(-1))、C3(0.15 kg·盆^(-1))4个梯度。灌水量设W1(90 mL·盆^(-1))、W2(140 mL·盆^(-1))、W3(190 mL·盆^(-1))、W4(240 mL·盆^(-1))、W5(290 mL·盆^(-1))5个梯度。[结果](1)在C2W3处理下土壤蔗糖酶活性最高,在C3W4处理下的过氧化氢酶活性最高;冬季时C2W4处理下土壤养分含量最大;春季时速效钾和有效磷在C2基肥施肥下含量最高,C3基肥施肥下的碱解氮和有机质含量最大;(2)在C3处理下速效钾、碱解氮对冬春季蔗糖酶和过氧化氢酶活性影响最大;其它养分在通过速效钾影响后,多个因素共同影响不同时期的蔗糖酶和过氧化氢酶活性;(3)结合茶树地上生长指标可知,茶树在C2基肥下株高、地径增长量最大,在W4灌水时叶分枝数增长量最大。[结论]随着越冬期的结束,钾元素不需要追肥补充,而茶树因生长需要须进行氮、磷元素的追肥补充;在240 mL·株^(-1)的灌水处理下茶树地上生长指标达到最大。

基于隆起变形分析的基坑坑底抗隆起稳定可靠度分析

采用土体硬化(Hardening Soil)模型,在PLAXIS 2D中建立基坑开挖数值模型,在获取坑底特征点隆起变形数据的基础上构建坑底隆起变形超限失效模式对应的极限状态函数,为提高计算效率,应用响应面法代替有限元计算快速获取坑底特征点隆起变形值,结合蒙特卡罗模拟方法进行坑底抗隆起稳定性可靠度分析,分析结果表明:第三层土的卸载再加载模量E_(3)^(ur)以及有效内摩擦角φ’_(3)的变异性对坑底抗隆起稳定性影响显著;第一层土的有效黏聚力c’_(1)、有效内摩擦角φ’_(1)、割线模量E_(1)^(50)、切线模量E_(1)^(oed)以及第二层土的有效黏聚力c’_(2)的变异性对坑底抗隆起稳定性影响较小,但相对而言,第二层土的有效黏聚力c’_(2)对坑底抗隆起稳定性的影响较大;对于坑底土体为粉砂的深基坑来说,对坑内土体进行加固可以有效约束坑底隆起变形。

Postponed and reduced basal nitrogen application improves nitrogen use efficiency and plant growth of winter wheat

Excessive nitrogen(N) fertilization with a high basal N ratio in wheat can result in lower N use efficiency(NUE) and has led to environmental problems in the Yangtze River Basin, China. However, wheat requires less N fertilizer at seedling growth stage, and its basal N fertilizer utilization efficiency is relatively low; therefore, reducing the N application rate at the seedling stage and postponing the N fertilization period may be effective for reducing N application and increasing wheat yield and NUE. A 4-year field experiment was conducted with two cultivars under four N rates(240 kg N ha–1(N240), 180 kg N ha–1(N180), 150 kg N ha–1(N150), and 0 kg N ha–1(N0)) and three basal N application stages(seeding(L0), fourleaf stage(L4), and six-leaf stage(L6)) to investigate the effects of reducing the basal N application rate and postponing the basal N fertilization period on grain yield, NUE, and N balance in a soil-wheat system. There was no significant difference in grain yield between the N180 L4 and N240 L0(control) treatments, and the maximum N recovery efficiency and N agronomy efficiency were observed in the N180 L4 treatment. Grain yield and NUE were the highest in the L4 treatment. The leaf area index, flag leaf photosynthesis rate, flag leaf nitrate reductase and glutamine synthase activities, dry matter accumulation, and N uptake post-jointing under N180 L4 did not differ significantly from those under N240 L0. Reduced N application decreased the inorganic N content in the 0–60-cm soil layer, and the inorganic N content of the L6 treatment was higher than those of the L0 and L4 treatments at the same N level. Surplus N was low under the reduced N rates and delayed basal N application treatments. Therefore, postponing and reducing basal N fertilization could maintain a high yield and improve NUE by improving the photosynthetic production capacity, promoting N uptake and assimilation, and reducing surplus N in soil-wheat systems.

Effect of Vachellia tortilis on understory vegetation,herbaceous biomass and soil nutrients along a grazing gradient in a semi-arid African savanna

The spatial pattern and abundance of herbaceous vegetation in semi-arid savannas are dictated by a complex and dynamic interaction between trees and grasses. Scattered trees alter the composition and spatial distribution of herbaceous vegetation under their canopies. Therefore, we studied the effect of Vachellia tortilis on herbaceous vegetation composition, biomass and basal area, and soil nutrients on sites with varying grazing intensities in the central rift valley of Ethiopia. Data were collected on species composition, cover and biomass of herbs and grasses, and soil moisture and nutrient contents under light,medium, and heavy grazing pressures, both under the inside and outside of V. tortilis canopies. Species richness was similar in both locations but decreased with increased grazing. Only the overall biomass and herb cover were significantly greater under the canopy than outside, and overall biomass showed significant unchanging decline with increased grazing. However, vegetation cover was significantly greater on moderately grazed sites compared to low and heavily grazed sites. All soil variables were significantly higher under V. tortilis canopies than outside.Our findings suggest that V. tortilis has more effect on composition and diversity of herbaceous vegetation than on species richness, and that V. tortilis promotes the herbaceous layer biomass by reducing soil moisture loss and increasing soil fertility under the inside than outside the canopies. Therefore, we suggest that management practices should be directed on reducing pressure on V. tortilis by regulating grazing. Low to moderate grazing levels(i.e., a stocking rate less than 39.6 TLU ha-1yr-1) seems to be tolerable to ensure sustainable conservation of the species in the study area in particular and in semi-arid savannas in general.

Land Use Effects on Soil Organic Carbon, Microbial Biomass and Microbial Activity in Changbai Mountains of Northeast China

Land use changes are known to alter soil organic carbon （SOC） and microbial properties, however, information about how conversion of natural forest to agricultural land use as well as plantations affects SOC and microbial properties in the Changbai Moun- tains of Northeast China is meager. Soil carbon content, microbial biomass carbon （MBC）, basal respiration and soil carbon mineraliza- tion were studied in five selected types of land use： natural old-growth broad-leaved Korean pine mixed forest （NF）; spruce plantation （SP） established following clear-cutting of NF; cropland （CL）; ginseng farmland （GF） previously under NF; and a five-year Mongolian oak young forest （YF） reforested on an abandoned GF, in the Changbai Mountains of Northeast China in 2011. Results showed that SOC content was significantly lower in SP, CL, GF, and YF than in NF. MBC ranged from 304.4 mg/kg in CL to 1350.3 mg/kg in NF, which was significantly higher in the soil of NF than any soil of the other four land use types. The SOC and MBC contents were higher in SP soil than in CL, GF, and YF soils, yielding a significant difference between SP and CL. The value of basal respiration was also higher in NF than in SP, CL, GF, and YF. Simultaneously, higher values of the metabolic quotient were detected in CL, GF, and YF soils, indicat- ing low substrate utilization of the soil microbial community compared with that in NF and SP soil. The values of cumulative mineral- ized carbon and potentially mineralized carbon （Co） in NF were significantly higher than those in CL and GF, while no significant dif- ference was observed between NF and SP. In addition, YF had higher values of Co and C mineralization rate compared with GF. The results indicate that conversion from NF into agricultural land （CL and GF） uses and plantation may lead to a reduction in soil nutrients （SOC and MBC） and substrate utilization efficiency of the microbial community. By contrast, soils below SP were more conducive to the preservation of soil organic matter, which was reflected in the comparison of microbial indicators among CL, GF, and YF land uses. This study can provide data for evaluating soils nutrients under different land use types, and serve as references for the rational land use of natural forest in the study area.

Salinity effects on soil organic carbon and its labile fractions,and nematode communities in irrigated farmlands in an arid region,northwestern China

The effects of salinity on soil organic carbon （SOC） and its labile fractions including microbial biomass carbon （MBC） and easily oxidation organic carbon （EOC）, basal soil respiration, and soil nematode community in the Fluvents, an oasis in an arid region of northwestern China were investigated. Five sites were selected which had a salinity gradient with different groundwater table from 1.0 m to 4.0 m. Soils were sampled at the 0~0 cm plough layer from 25 irrigated fields of five sites and electrical conductivity was measured in the saturation paste extracts （ECe）. Soils were categorized into five salinity levels： （1） non-saline, （2） very slightly saline, （3） slightly saline, （4） moderately saline, and （5） strongly saline according to the values of ECe. The results show that SOC and total nitrogen concentration, cation exchange capacity （CEC）, and the concentrations of labile organic fractions （MBC, EOC）, and basal soil respiration decreased significantly with increasing ECe. The relationships between ECe and MBC, EOC and basal soil respiration were best described by power functions. Slight and moderate salinity had no significant impact on soil nematode abundance, but excessive salt accumulation led to a marked decline in soil nematode community diversity and abundance. Soil salinity changed soil nematode trophic groups and bacterivores were the most abundant trophic groups in salt-affected soils. Further study is necessary to identify the response of soil microbial processes and nematode community dynamics to soil salinity.

Effects of recovery time after fire and fire severity on stand structure and soil of larch forest in the Kanas National Nature Reserve, Northwest China

Forest recovery may be influenced by several factors, of which fire is the most critical.However, moderate-and long-term effects of fire on forest recovery are less researched in Northwest China.Thus, the effects of different forest recovery time after fire(1917(served as the control), 1974, 1983 and 1995) and fire severities(low, moderate and high) on larch(Larix sibirica Ledeb.) forest were investigated in the Kanas National Nature Reserve(KNNR), Northwest China in 2017.This paper analyzed post-fire changes in stand density, total basal area(TBA), litter mass, soil organic carbon(SOC) and soil nutrients(total nitrogen, total phosphorus and total potassium) with one-way analyses of variance.Results indicate that litter mass, TBA, SOC and soil nutrients increased with increasing recovery time after fire and decreasing fire severity, while the stand density showed an opposite response.The effects of fire disturbance on SOC and soil nutrients decreased with increasing soil depth.Moreover, we found that the time of more than 43 a is needed to recover the litter mass, TBA, SOC and soil nutrients to the pre-fire level.In conclusion, high-severity fire caused the greatest variations in stand structure and soil of larch forest, and low-severity fire was more advantageous for post-fire forest stand structure and soil recovery in the KNNR.Therefore, low-severity fire can be an efficient management mean through reducing the accumulation of forest floor fuel of post-fire forests in the KNNR, Northwest China.

Four years of free-air CO_2 enrichment enhance soil C concentrations in a Chinese wheat field

Elevated atmospheric CO2 can influence soil C dynamics in agroecosystems. The effects of free-air CO2 enrichment （FACE） and N fertilization on soil organic C （Corg）, dissolved organic C （DOC）, microbial biomass C （Cmic） and soil basal respiration （SBR） were investigated in a Chinese wheat field after expose to elevated CO2 for four full years. The results indicated that elevated CO2 has stimulative effects on soil C concentrations regardless of N fertilization. Following the elevated CO2, the concentrations of Corg and SBR were increased at wheat jointing stage, and those of DOC and Cmic were enhanced obviously across the wheat jointing stage and the fallow period after wheat harvest. On the other hand, N fertilization did not significantly affect the content of soil C. Significant correlations were found among DOC, Cmic, and SBR in this study.

Toxicity of cadmium to soil microbial biomass and its activity:Effect of incubation time on Cd ecological dose in a paddy soil

Cadmium (Cd) is ubiquitous in the human environment and has toxic effect on soil microbial biomass or its activity, including microbial biomass carbon (Cmic), dehydrogenase activity (DHA) and basal respiration (BR), etc., Cmic, DHA, BR were used as bioindicators of the toxic effect of Cd in soil. This study was conducted to determine the effects of Cd on soil microbial biomass and its activity in a paddy soil. The inhibition of microbial biomass and its activity by different Cd concentrations was described by the kinetic model (M1) and the sigmoid dose-response model (M2) in order to calculate three ecological doses of Cd: ED50, ED10 and ED5. Results showed that M2 was better fit than M1 for describing the ecological toxicity dose effect of cadmium on soil microbial biomass and its activity in a paddy soil. M2 for ED values (mg/kg soil) of Cmic, DHA, BR best fitted the measured paddy soil bioindicators. M2 showed that all ED values (mg/kg) increased in turn with increased incubation time. ED50, ED10 and ED5 of Cmic with M2 were increased in turn from 403.2, 141.1, 100.4 to 1000.7, 230.9, 144.8, respectively, after 10 d to 60 d of incubation. ED50, ED10 and ED5 of DHA with M2 increased in turn from 67.6, 6.2, 1.5 to 101.1, 50.9, 41.0, respectively, after 10 d to 60 d of incubation. ED50, ED10 and ED5 of BR with M2 increased in turn from 149.7, 6.5, 1.8 to 156.5, 50.8, 35.5, respectively, after 10 d to 60 d of incubation. So the ecological dose increased in turn with increased incubation time for M2 showed that toxicity of cadmium to soil microbial biomass and its activity was decreased with increased incubation time.

Soil Microbial Population in the Vicinity of the Bean Caper(Zygophyllum dumosum)Root Zone in a Desert System

The aim of the current study was to gain a better understanding of the changes in soil microbial biomass and basal respiration dynamics in the vicinity of the bean caper （Zygophyllura duraosura） perennial desert shrub and the inter-shrub sites. Microbial biomasses as well as basal respiration were found to be significantly greater in the soil samples taken beneath the Z. duraosura shrubs than from the inter-shrub sampling sites, with no differences between the two sampling layers （0-10 and 10-20 cm） throughout the study period. However, seasonal changes were observed due to autumn dew formation, which significantly affected microbial biomass and basal respiration in the upper-layer inter-shrub locations. The calculated metabolic coefficient （qCO2） revealed significant differences between the two sampling sites as well as between the two soil layers, elucidating the abiotic effect between the sites throughout the study period. The substrate availability index was found to significantly demonstrate the differences between the two sites, elucidating the significant contribution of Z. duraosura in food source availability and in moderating harsh abiotic components. The importance of basal microbial parameters and the derived indices as tools demonstrated the importance and need for basic knowledge in understanding plant-soil interactions determined by an unpredictable and harsh desert environment.

A Comparative Study on the Microbiological Characteristics of Soils Under Different Land—Use Conditions from Karst Areas of Southwest China

Microbiological and physical\|chemical characteristics of subtropical forest, grassland and cropfield soils from the karst areas of Southwest China were investigated. The study revealed that the conversion of natural forest to other forms of land would lead to a reduction in soil organic C(26.2%-35.3%), total N(37.2%-55.8%), total P(32.9%-43.6%), microbial biomass C(35.4%-49.1%), N(37.2%-55.8%), and P(25.8%-41.9%). Comparative analysis of microbial activity in terms of basal soil respiration showed maximum activity in forest soil and minimum in cropfield soil. Analysis of microbial metabolic respiratory activity indicated a relatively greater respiratory loss of CO\-2—C per unit microbial biomass in cropfield and grassland than in forest soil. Considering the importance of microbial components in soil, it is concluded that land use in different ways will lead to the reduction of biological stability of soil.

Basal Application of Zinc to Improve Mung Bean Yield and Zinc-Grains-Biofortfication

Worldwide,the dietary deficiency of zinc(Zn)is prevailing in almost all arid and semi-arid regions.Zinc deficiency is not only the major constraint of lower yield,but also dietary Zn deficiency in cereals grains may cause increasing malnutrition and chronic health problems in human.Exogenous application of Zn through basal soil nutrition might be a useful option to recover Zn deficiency in mung bean.Therefore,field study was conducted to optimize the optimum level and method of Zn nutrition to enhance crop yield and Zn biofortification of mung bean through basal application.Zinc was applied at 0,5,10 and 15 kg/ha as basal application and side dressing,and in combination(50%basal application+50%side dressing).The results highlighted that Zn nutrition prominently improved the mung bean yield as compared with control(no Zn applied).The maximum grains yield and Zn concentration in grains were obtained where Zn was applied at 15 kg/ha as basal application as compared with all other combinations.Better improvement in grain yield was due to significant increase in more number of pods and grain size owing to well-developed root system,improved leaf area index and high chlorophyll contents in mung beans leaves.Amongst all applied Zn nutrition’s the basal application of Zn(15 kg/ha)was a viable option to get higher yield and Zn biofortification of mung bean.

小兴安岭红松胸高断面积生长随树龄的变化规律及主要影响因素

【目的】揭示红松胸高断面积生长随树龄的变化规律,探究其在不同生长阶段的主要影响因素,为理解树龄、环境因子和功能性状在树木生长和经营中的重要性提供科学依据。【方法】于黑龙江凉水国家级自然保护区内采集不同树龄(16~285年)红松样树65株,采用胸高断面积生长率(BAGR)表征树木径向生长,测定树木所处的环境因子(光照强度、土壤养分、土壤含水量、土壤pH)和功能性状(叶、枝、根性状),探究红松胸高断面积生长随树龄的变化规律及主要影响因素。【结果】1)红松BAGR随树龄增加呈先增大后减小的变化趋势,树龄小于220年时BAGR随树龄增加而增大,大于220年时BAGR随树龄增加而减小;2)树龄、光照强度和土壤pH对红松幼龄树(16~100年)BAGR存在正向影响,比叶面积对幼龄树BAGR存在负向影响;3)土壤氮含量和木质密度对红松中龄树(100~220年)BAGR存在显著负向影响;4)树龄显著抑制红松老龄树(大于220年)胸高断面积生长,根氮含量及多年生针叶单位质量氮和磷含量促进老龄树胸高断面积生长,且根氮含量的影响更加显著。【结论】树龄、环境因子和功能性状共同驱动红松径向生长,影响效果随树龄变化而异;限制红松生长的资源条件随树龄增加由光照转为土壤养分和自身生理因素。

施肥对我国农田土壤基础呼吸的影响

【目的】基础呼吸是反映土壤质量的重要指标,采用整合分析研究施肥对我国不同种植制度和气候带农田基础呼吸的影响程度及其关键控制因素,为探究土壤肥力提升提供科学依据。【方法】通过以“施肥”、“土壤呼吸”、“有机碳矿化”、“soil CO_(2)efflux/soil CO_(2)emission”、“农田”为关键词,在Web of Science、中国知网、万方数据库,收集2000-2020年发表的相关文献,建立了586组配对试验数据,对肥料类型、施肥年限、施氮量、气候带、种植制度、利用方式等条件下的土壤基础呼吸数据进行标准化,采用Meta-analysis分析了土壤理化性状和生产条件指标对土壤基础呼吸的影响程度。【结果】与不施肥相比,施肥对土壤基础呼吸的提高幅度平均为60.20%,其中,施用有机肥的提高幅度为81.45%,显著高于施用化肥的47.78%。当施肥年限大于30年时,施用有机肥对土壤基础呼吸的提升幅度是施用化肥处理的1.38倍。适宜氮肥投入量[N 100~200 kg/(hm^(2)·a)]引发的土壤基础呼吸增幅(72.56%)大于高量[>200 kg/(hm^(2)·a)]和低量[<100 kg/(hm^(2)·a)]氮肥投入的增幅(44.65%和55.21%)。中温带地区施肥导致的土壤基础呼吸增幅(93.71%)显著高于亚热带(37.11%)和暖温带(40.64%)地区,施用化肥和有机肥对中温带地区土壤基础呼吸的提升效果(73.88%和110.91%)显著高于对亚热带地区(28.99%和45.00%)。施肥对旱地土壤基础呼吸的提升幅度(105.01%)显著高于对水田(28.90%)和水旱轮作(46.90%)。轮作模式下施肥对基础呼吸的提升幅度(101.60%)显著高于连作模式(50.63%)。相关性分析结果表明,土壤基础呼吸与土壤有机碳、全氮及微生物生物量碳、氮呈显著正相关。此外,施用有机肥处理下,土壤基础呼吸与碱解氮和微生物熵呈显著正相关。【结论】施肥对农田土壤基础呼吸的作用受到施肥年限、氮肥投入量、气候带、土地利用类型、种植制度、土壤质地等因素的共同影响。施肥能够显著提升土壤有机碳含量,并提高土壤基础呼吸。在较长时间(>30年)尺度上,施用有机肥相较于化肥能够显著提高土壤微生物生物量碳以及微生物熵,进而提高土壤基础呼吸,表明施用有机肥对土壤质量提升有积极的促进作用。

高碳基肥料穴施用量对烤烟生长发育及土壤理化性质的影响

采用田间试验研究了不同高碳基肥料穴施用量对烟株生长和根系发育以及土壤理化性质的影响。结果表明,穴施高碳基肥料对烟株的主要农艺性状影响不明显,但可以显著增加打顶后烟株的最大叶长和最大叶宽,且增幅随高碳基肥料用量的增加而加大。烟株移栽后45和60 d的根系体积、根鲜重、根干重、根系活力都与穴施用量呈正相关关系,穴施高碳基肥料能够有效促进烟株根系生长发育,且随着高碳基肥料用量增加,促生效果增大。穴施高碳基肥料可以提高根区土壤pH、全氮含量、全碳含量和碳氮比,能有效提高根区土壤速效养分含量,速效钾、有效磷、铵态氮和硝态氮分别提高7.80%~25.25%、15.84%~29.00%、20.04%~44.23%和20.52%~45.46%,高碳基肥料对根区土壤硝态氮和铵态氮的提升效果高于有效磷和速效钾,对根区土壤有效磷的提升效果略高于速效钾。T_(2)处理(20 g/穴)和T_(3)处理(30 g/穴)对促进烟株生长发育、提高根区土壤肥力、促进植烟土壤改良效果明显。综合来看,郴州烟区高碳基肥料的适宜施用量为每穴约25 g。

膜下滴灌条件下氮钾肥基追比对风沙地土壤养分、酶活性及花生产量的影响

为提高东北农牧交错区花生的科学施肥效果,明确水肥一体化条件下肥料最佳的基追比例,在田间膜下滴灌条件下,设计了不同基追比(每公顷施用氮肥68.18 kg,磷肥22.08 kg,钾肥174.33 kg;磷肥全部用作基肥,氮肥和钾肥按全部施肥量的0、20%、40%、60%、80%和100%作为追肥),分别于苗期、开花下针期、结荚期、饱果期各施肥1次,即T0、T20、T40、T60、T80和T100处理,其余作为基肥。研究调查了不同基追比对风沙地土壤养分、酶活性及花生产量的影响。结果表明:土壤有机质含量、速效氮含量、脲酶活性和蔗糖酶活性随追肥比例的增加而增加,随土层厚度的增加而降低;随着追肥比例的增加,花生产量呈先增高后降低的趋势,均比传统施肥方式T0有所提高,两年增产幅度为3.77%~41.27%;在T60时产量达到最高,分别为6427.7 kg/hm^(2)和6046.8 kg/hm^(2);全部用作追肥时增产不明显,两年平均增产4.53%。综上所述,田间水肥一体化条件下,全部施肥量的40%用作底肥,60%用作追肥时效果最佳。

不同土种土壤氮素等养分与水稻基础产量的关系

通过对不同土种土壤养分测定及不施氮肥空白区试验,分析不同土种土壤氮素等养分与水稻基础产量的关系,研究不同土种不施氮肥空白区每100 kg基础产量稻谷需氮量及土壤氮素当季利用率。结果表明:①水稻土类4个土种土壤有机质、全氮、碱解氮、速效钾含量及不施氮肥空白区水稻基础产量明显高于潮土类4个土种,速效磷含量两者较为接近;②同一土种不同农田土壤中全氮、有机质与碱解氮的含量相对稳定,空间变异相对较小;③8个土种土壤有机质含量与水稻基础产量均呈极显著正相关;④8个土种土壤有机质含量均对不施氮肥空白区水稻基础产量起关键作用,且极显著大于全氮、碱解氮、速效磷、速效钾所起的作用;⑤根据土壤养分测定及不施氮肥空白区试验结果,建立了不同土种不施氮肥空白区水稻基础产量模型,模拟值与实测值吻合度较高;⑥潮土类4个土种不施氮肥空白区每100 kg稻谷平均需氮量为1.48 kg,水稻土类4个土种则为1.69 kg;⑦潮土类4个土种土壤氮肥当季平均利用率为46.4%,而水稻土类4个土种土壤氮肥当季平均利用率为41.6%。

26年长期施肥对土壤微生物量碳、氮及土壤呼吸的影响

研究长期小麦连作施肥条件下土壤微生物量碳、氮,土壤呼吸的变化及其与土壤养分的相关性。以陕西长武长期定位试验为平台,应用氯仿熏蒸-K2SO4提取法、碱液吸收法和化学分析法分析了长达26a不同施肥处理农田土壤微生物量碳、微生物量氮和土壤呼吸之间的差异及其调控土壤肥力的作用。长期施肥及种植作物,均能提高土壤微生物量碳、氮含量,尤其是施用有机肥,土壤微生物量碳、氮含量高于单施无机肥的处理,土壤呼吸量也提高15.91%—75.73%,而施用无机肥对于土壤呼吸无促进作用。土壤微生物生物量碳氮、土壤呼吸与土壤有机质、全氮呈极显著相关。长期有机无机肥配施可以提高土壤微生物量碳氮、土壤呼吸,氮磷肥与厩肥配施对提高土壤肥力效果最好。微生物量碳氮及土壤呼吸可以反映土壤质量的变化,作为评价土壤肥力的生物学指标。

水分条件对水稻土微生物群落多样性及活性的影响

采用BIOLOG碳素利用法、磷脂脂肪酸(PLFA)法和土壤酶活性测定等方法比较了三种水分条件(淹育、淹育晾干、非淹育)对水稻土微生物群落多样性及活性的影响。结果表明,淹育处理水稻土的脱氢酶、蔗糖酶活性明显高于淹育晾干和非淹育处理,并导致该土壤的基础呼吸升高。BIOLOG碳素利用法表明,非淹育处理的微生物群落平均吸光值(AWCD)显著低于淹育和淹育晾干处理。磷脂脂肪酸(PLFA)实验发现,淹育水稻土的真菌特征脂肪酸(18∶2w6,9c)所占比例减少,真菌特征脂肪酸(18∶2w6,9c)与细菌特征脂肪酸(15∶0i+15∶0a+16∶0i+16∶1w5c+17∶0i+17∶0a+17∶0cy+17∶0+18∶1w7c+19∶0cy)的比值下降;水分条件变化没有改变土壤微生物环丙基脂肪酸19∶0cy的相对丰度,但非淹育处理的环丙基脂肪酸17∶0cy相对丰度明显高于另外二种处理。BIOLOG碳素利用法的群落水平生理剖面(CLPP)和磷脂脂肪酸(PLFA)测定结果经聚类分析后,发现淹育和淹育晾干处理的土壤微生物多样性在较低的距离尺度可聚成一类,且与非淹育土壤具有明显差异。淹育水稻土与淹育晾干相比,尽管土壤微生物群落结构和功能多样性有一定的相似性,但微生物的种群组成和活性仍发生了较大的变化。