Rhizosphere organic phosphorus fractions of Simon poplar and Mongolian pine plantations in a semiarid sandy land of northeastern China

The aim of this study was to investigate the role of rhizosphere organic phosphorus(P) in soil P supply in semiarid forests and the effects of tree species on rihizosphere organic P. We examined organic P fractions in rhizosphere and bulk soils of mono-specific Simon poplar(Populus simonii) and Mongolian pine(Pinus sylvestris var. mongolica) plantations in a semiarid sandy soil of Horqin Sandy Land in Northeast China. Total organic P(TPo) accounted for 76% of total P across the two stands. The concentration of organic P(Po) fractions decreased in the order of Na OH-Po>Res-Po>HCl-Po>Na HCO3-Po in both plantations. The concentration of Na HCO3-Po was 38% and 43% lower in rhizosphere soil than in bulk soil in Simon poplar and Mongolian pine plantations, respectively. In contrast, total P, TPo and Na OH-Po significantly accumulated in rhizosphere soil in Simon poplar plantations, but no change in Mongolian pine plantations. Soil recalcitrant organic P fractions were positively correlated with soil organic carbon. The results suggest that rhizosphere labile organic P was an important source of plant-available P in this semiarid region, but the dynamic of rhizosphere recalcitrant organic P fractions varied with tree species and was correlated to organic carbon dynamics.     

Potato absorption and phytoavailability of Cd,Ni, Cu,Zn and Pb in sierozem soils amended with municipal sludge compost

Effects of sludge utilization on the mobility and phytoavailability of heavy metals in soil-plant systems have attracted broad attention in recent years. In this study, we analyzed the effects of municipal sludge compost(MSC) on the solubility and plant uptake of Cd, Ni, Cu, Zn and Pb in a soil-potato system to explore the mobility, potato plant uptake and enrichment of these five heavy metals in sierozem soils amended with MSC through a potato cultivation trial in Lanzhou University of China in 2014. Ridge regression analysis was conducted to investigate the phytoavailability of heavy metals in amended soils. Furthermore, CaCl_2, CH_3 COONH_4, CH_3COOH, diethylene triamine pentacetic acid(DTPA) and ethylene diamine tetraacetic acid(EDTA) were used to extract the labile fraction of heavy metals from the amended soils. The results show that the MSC could not only improve the fertility but also increase the dissolved organic carbon(DOC) content of sierozem soils. The total concentrations and labile fraction proportions of heavy metals increase with increasing MSC percentage in sierozem soils. In amended soils, Cd has the highest solubility and mobility while Ni has the lowest solubility and mobility among the five heavy metals. The MSC increases the concentrations of heavy metals in the root, stem, peel and tuber of the potato plant, with the concentrations being much higher in the stem and root than in the peel and tuber. Among the five heavy metals, the bioconcentration factor value of Cd is the highest, while that of Ni is the lowest. The complexing agent(DTPA and EDTA) extractable fractions of heavy metals are the highest in terms of phytoavailability. Soil properties(including organic matter, p H and DOC) have important impacts on the phytoavailability of heavy metals. Our results suggest that in soil-potato systems, although the MSC may improve soil fertility, it can also increase the risk of soils exposed to heavy metals.     

Micronutrient Distribution in Different Physiographic Units of the Siwalik Hills of the Semiarid Tract of Punjab,India

We investigated the profile distribution of total and diethylenetriamine pentaacetic acid ( DTPA )- extractable micronutrients ( Zn , Mn , Cu , Fe ) in soils developed on six physiographic units of the semiarid Siwalik hills of Punjab in northwest India . The soils showed a gradual fining of texture from shoulder slopes to toe slopes . All soils were alkaline and calcareous . In general , total and DTPA-extractable micro nutrients were higher in surface horizons and decreased in subsurface horizons . However , none of the micronutrients exhibited any consistent pattern of distribution with depth on different geomorphic surfaces . Physiography had a strong influence on the spatial distribution of total and available micronutrients . Contents of all micronutrients and their forms were higher in fine-textured and uneroded soils than in coarse-textured eroded soils . Soil pH , calcium carbonate , organic matter , and size fractions had strong influence on the distribution of total and extractable micronutrients . Based on linear coefficients of correlation , total content of micro nutrients increased with increase in clay content , whereas DTPA - extractable micronutrient content increased with increase in organic carbon and decreased with increase in pH and CaCO3 content . Except for Cu , no other micronutrient showed influence of total reserves on availability of the respective micronutrient . Among the various micronutrients , deficiency of Zn was found to be widespread , followed by Fe and Cu in the cultivated soils on foot slopes , toe slopes , and floodplains .     

Influence of Dissolved Organic Carbon and Initial Moisture on Zinc Sorption by Two Arid Soils

Sorption of added zinc to irrigated soils in arid regions is an important process that may control the availability of zinc to growing plants . Two soil surface samples varying in clay , organic matter , and calcium carbonate content were selected from central and southwestern regions of Saudi Arabia and prepared in order to give different initial moisture contents ranging from air dried to 100 % of field capacity . The sorption experiment was conducted using Zn concentrations ranging from 5 to 25 mg L 1, prepared from ZnSO4 either in distilled water or in solutions containing 75 mg L 1 dissolved organic carbon (DOC). Results indicate that the amount of Zn sorbed in the presence of DOC was relatively high compared with the absence of DOC and Zn retention was strongly affected by the initial soil moisture content . Also , equilibrium Zn concentrations were quite low , while Zn retentions were high in all treatments . Data of Zn sorption were described by the Freundlich isotherm , and two linear portions were found in most cases . In the absence of DOC , retentions of added Zn were controlled by the available exchange sites and / or the precipitation of Zn as sparingly soluble forms. Zn ions in the presence of DOC were able to form soluble - Zn organic complexes that adsorb on the soil surfaces . The extent of such behavior was related to the variations in clay , organic matter , and calcium carbonate contents as well as the initial moisture of the soil . Results indicate that addition of DOC reduces the amount of extractable Zn from either soil Zn or the sorbed Zn by ammonium bicarbonate diethylenetriamine pentaacetic acid ( AB DTPA ). More than 80 % of the sorbed Zn was extracted by AB-DTPA , and the percentage of extracted / sorbed Zn decreased with the increase in sorbed Zn . The obtained results give evidence that initial moisture content and addition of DOC reduce the extractability of applied inorganic Zn by AB-DTPA extract in arid soils.     

连续多年不同灌溉方式对保护地土壤磷剖面分布的影响

自以同一方案连续12 a进行定位灌溉试验的栽培番茄保护地,分层采集0~100 cm土层的土壤样本,研究了灌溉方式对保护地土壤全磷、速效磷(Olsen-P)含量及其剖面分布的影响。结果表明,0~60 cm土层土壤全磷、速效磷含量明显高于60~100 cm土层;土层不同灌水处理间土壤全磷、速效磷含量及其剖面分布0~60 cm土层表现出了明显差异,总体上沟灌和滴灌高于渗灌,而沟灌和滴灌之间差异不明显;速效磷占全磷比例在0~40 cm土层以滴灌处理为最高,其它两灌溉处理相对较低;与滴灌、渗灌处理不同,沟灌处理土壤的速效磷占全磷比例随土层深度增加变化不明显。相关分析结果表明,各灌溉处理土壤速效磷与全磷之间呈极显著正相关关系,而全磷、速效磷含量与有机质间呈显著的指数正相关关系。     

长期秸秆还田对褐土农田土壤有机碳、氮组分及玉米产量的影响

基于1992—2022年连续30 a的长期定位试验,研究秸秆不还田（CK）、秸秆覆盖还田（SM）、秸秆粉碎直接还田（SC）和秸秆过腹还田（CM）4种不同秸秆还田方式对土壤有机碳、氮组分和作物产量的影响。结果表明：（1）不同秸秆还田方式均可增加耕层土壤有机碳、全氮及其组分含量;与CK相比,CM处理0~20 cm土层土壤的总有机碳（SOC）、轻组有机碳（LFOC）、微生物量碳（MBC）、水溶性有机碳（DOC）和颗粒有机碳（POC）的含量分别显著增加42.85%、93.51%、80.09%、190.42%和123.38%;土壤全氮（TN）、轻组有机氮（LFON）、微生物量氮（MBN）、水溶性有机氮（WSON）和颗粒有机氮（PON）的含量分别显著增加49.37%、34.26%、69.49%、172.73%和129.29%。（2）各活性有机碳组分与土壤有机碳的比值表现为LFOC>POC>MBC>DOC;各氮组分与土壤全氮的比值表现为LFON>PON>MBN>WSON。（3）CM和SC处理下敏感指数最高的指标为DOC,DOC可作为CM和SC处理早期有机物变化的指示物;SM处理下敏感指数最高的指标为LFOC,LFOC可作为SM处理早期有机物变化的指示物。（4）土壤有机碳、氮组分间均呈显著正相关关系,其中DOC可以较好地反映SOC的变化情况,WSON可较好地反映TN的变化情况。（5）与CK相比,长期秸秆还田均可以显著提高玉米产量,SM、SC和CM处理30 a累计产量分别增加6.38%、7.82%和23.00%。综上,长期秸秆还田是提高土壤有机碳氮组分含量和作物产量的有效耕作措施,以秸秆过腹还田效果最为突出,可在黄土高原旱地玉米种植区域推广。     

Potato brown rot incidence and severity under different management and amendment regimes in different soil types

Ralstonia solanacearum race 3 biovar 2, the causative agent of potato brown rot (bacterial wilt), is an economically important disease in tropical, subtropical and temperate regions of the world. In view of previous reports on suppression of the disease by organic amendments, and the expansion of organic agriculture, it was timely to compare the effects of organic and conventional management and various amendments on brown rot development in different soils (type: sand or clay; origin: Egypt or the Netherlands). Brown rot infection was only slightly reduced in organically compared to conventionally managed sandy soils from Egypt, but organic management significantly increased disease incidence and pathogen survival in Dutch sandy and clay soils, which correlated with high DOC contents in the organic Dutch soils. There was no correlation between disease incidence or severity and bacterial diversity in the potato rhizosphere in differently managed soils (as determined by 16S DGGE). NPK fertilization reduced bacterial wilt in conventional Egyptian soils but not in Dutch soils. Cow manure amendment significantly reduced disease incidence in organic Dutch sandy soils, but did not affect the bacterial population. However, cow manure did reduce densities of R. solanacearum in Egyptian sandy soils, most probably by microbial competition as a clear shift in populations was detected with DGGE in these and Dutch sandy soils after manure amendment. Amendment with compost did not have a suppressive effect in any soil type. The absence of a disease suppressive effect of mineral and organic fertilization in Dutch clay soils may be related to the already high availability of inorganic and organic nutrients in these soils. This study shows that the mechanism of disease suppression of soil-borne plant pathogens may vary strongly according to the soil type, especially if quite different types of soil are used.     

Corn straw return can increase labile soil organic carbon fractions and improve water-stable aggregates in Haplic Cambisol

Corn straw return to the field is a vital agronomic practice for increasing soil organic carbon (SOC) and its labile fractions, as well as soil aggregates and organic carbon (OC) associated with water-stable aggregates (WSA). Moreover, the labile SOC fractions play an important role in OC turnover and sequestration. The aims of this study were to determine how different corn straw returning modes affect the contents of labile SOC fractions and OC associated with WSA. Corn straw was returned in the following depths: (1) on undisturbed soil surface (NTS), (2) in the 0-10 cm soil depth (MTS), (3) in the 0-20 cm soil depth (CTS), and (4) no corn straw applied (CK). After five years (2014-2018), soil was sampled in the 0-20 and 20-40 cm depths to measure the water-extractable organic C (WEOC), permanganate oxidizable C (KMnO₄-C), light fraction organic C (LFOC), and WSA fractions. The results showed that compared with CK, corn straw amended soils (NTS, MTS and CTS) increased SOC content by 11.55%-16.58%, WEOC by 41.38%-51.42%, KMnO₄-C and LFOC by 29.84%-34.09% and 56.68%-65.36% in the 0-40 cm soil depth. The LFOC and KMnO₄-C were proved to be the most sensitive fractions to different corn straw returning modes. Compared with CK, soils amended with corn straw increased mean weight diameter by 24.24%-40.48% in the 0-20 cm soil depth. The NTS and MTS preserved more than 60.00% of OC in macro-aggregates compared with CK. No significant difference was found in corn yield across all corn straw returning modes throughout the study period, indicating that adoption of NTS and MTS would increase SOC content and improve soil structure, and would not decline crop production.     

不同培肥方式对黑土供磷能力的影响

利用采自海伦农田生态系统国家野外科学观测研究站长期定位试验地的三个施肥处理:无肥(CK)、化肥(NP)、化肥配施有机肥(NPM)的土壤进行框栽试验,研究了不同培肥方式对黑土供磷能力的影响。结果表明:CK、NP、NPM土壤中的有机磷都能自然矿化,其中CK土壤有机磷矿化能力较弱,而NP、NPM土壤有机磷矿化能力较强,并且种植作物有利于土壤磷的矿化;CK土壤基础供磷能力较弱,施用磷肥可提高CK土壤的供磷能力,而NP、NPM土壤基础供磷能力较强,施用磷肥对土壤供磷能力影响不大;长期种植作物不施磷肥土壤中的磷处于耗竭状态,施NK肥种植作物处理能加剧土壤中磷的消耗;CK土壤供磷能力较弱,作物对土壤磷的依存率较低,对磷肥的利用率高,施用磷肥增产效果明显;NP、NPM土壤供磷能力较强,作物对土壤磷的依存率较高,对磷肥的利用率低,施用磷肥增产效果不大。     

盐碱土微生物功能群季节动态与土壤理化因子的关系

选取河西走廊东端永登县6种盐碱土壤类型,对各样地微生物功能群的季节动态与土壤理化因子之间的关系进行分析.结果表明:①盐碱环境中土壤细菌＞放线菌＞真菌,细菌和放线菌数量在夏季出现峰值,真菌数量在秋季和冬季出现峰值;不同微生物功能群基本上只有一个峰值且峰值出现的季节不同,与碳循环相关的纤维素分解菌功能群的峰值出现在冬季,与...     

陇东旱塬地表覆盖方式对苹果生育后期叶片质量及根际土壤微环境的影响

为探明陇东旱塬区不同覆盖方式对苹果生育后期叶片质量、根际生态环境的影响,以16 a生,连续6 a覆盖的盛果期“长富2号”苹果树为试材,设清耕（CK)、覆膜、麦草覆盖、覆黑膜+麦草（膜+草）等4个处理,调查叶片养分、活性氧代谢功能,测定0～100 cm内不同深度土层土壤水分、容重、有机质等,对根际土壤微生物数量及土壤酶活性进行分析。结果表明：麦草覆盖处理可有效提高苹果叶片叶绿素与淀粉含量,增幅分别为CK的2.79%、29.09%;根系集中分布层（20～40 cm）土壤水分、有机质含量增高,分别为CK的102.93%,135.96%;土壤容重仅为CK的96.32%,并有效提高各土层土壤酶活性,特别提高土壤表层（0～20 cm）酶活性,脲酶、碱性磷酸酶、过氧化氢酶、蔗糖酶活性为CK的157.14%、218.5%、118.02%、193.21%,可有效提高土壤中微生物总量,为CK的134.19%,其中细菌与真菌的数量增高,放线菌的数量降低;根系活力与土壤水分、孔隙度、微生物含量及脲酶、蔗糖酶等呈极显著正相关,与土壤容重、过氧化氢酶呈极显著负相关。覆膜与膜+草处理对叶片及土壤环境改善效果较差。综合分析根际土壤理化性状及土壤酶、微生物空间分布特征等,认为麦草覆盖处理是陇东旱塬区苹果园适宜的地表覆盖方式。     

The interdependent effects of solar disinfestation and compost maturity level on soil microbial activity

The combined effects of soil solarization and application of compost of various maturity levels upon soil microbial activity were studied under field conditions during 2010–2012. Eight treatments were divided into solarized and non-solarized treatments, and each was either non-amended or annually amended with compost at 6 kg (DW) m^-2. The composts were mature, partially mature, or immature. In all three tested parameters of microbial activity (respiration rate, heat output, and dehydrogenase activity) the immature compost showed higher activity than the other compost types. Soil samples were collected weekly in order to assess microbial activity, which was evaluated from measurements of soil respiration rate, heat output, and dehydrogenase activity. Significant and year-to-year reproducible differences in all three parameters were observed between soils amended with the three compost types. Some residual (carry-over) effects of previous-year treatments were obtained. Microbial activity decreased in both solarized and non-solarized treatments during the experimental period, probably because of increasing summer temperatures, but the decline was sharper in the solarized treatments probably due to oxygen deficiency under the tarp. Significantly higher activity was found in the treatments amended with the immature compost, both in the solarized and non-solarized treatments. This could be a result of the high level of dissolved organic matter in the immature compost, which enhanced microbial activity.     

Influence of zinc sulfate and municipal solid waste compost on chemical forms of zinc in calcareous soils

Zinc (Zn) is an essential micronutrient for crop growth. This metal can be found in chemical forms or fractions in the soil. The objective of this study was to investigate the distribution of Zn in special chemical forms using the sequential extraction method after treating eight calcareous soils by zinc sulfate and municipal solid waste (MSW) compost. Zn was separated in seven defined forms as exchangeable (Ex), carbonate (Car), organic (Om), manganese oxide bound (MnOX), amorphous iron oxide bound (FeAOX), crystalline iron oxide bound (FeCOX), and residual (Res). According to the results, the mean concentrations of Zn in chemical forms in untreated soils from higher to lower were 31.84, 8.13, 2.64, 2.57, 0.45, 0.39, and 0.16?mg?kg^?1 for the Res, FeCOX, Car, FeAOX, Om, MnOX, and Ex forms, respectively. The total applied Zn to the studied soils from both the sources of zinc sulfate and MSW compost after incubation for 30 days was converted to chemical forms in the following order: Car?>?Res?>?FeCOX?>?Om?>?FeAOX?>?MnOX?>?Ex. On average, 30.3% of total Zn from zinc sulfate and 28.8% of total Zn in the MSW compost were converted into the Car form. The high content of calcium carbonate (CaCO₃) in the studied soils is an important factor affecting the conversion of Zn forms, mostly in the Car form through the application of both the inorganic and the organic sources of Zn.     

Short-term fluctuations of sugar beet damping-off by Pythium ultimum in relation to changes in bacterial communities after organic amendments to two soils

Previously, oscillations in beet seedling damping-off by Pythium ultimum, measured as area under the disease progress curve (AUDPC), were demonstrated after incorporation of organic materials into organic and conventional soils. These periodic fluctuations of P. ultimum infections were cross-correlated with oscillations of copiotrophic CFU at lags of 2 to 4 days. For this article, we investigated whether bacterial communities and microbial activities fluctuated after a disturbance from incorporation of organic materials, and whether these fluctuations were linked to the short-term oscillations in AUDPC of beet seedling damping-off and bacterial populations (CFU) in soil. Soil microbial communities studied by polymerase chain reaction-DGGE analysis of 16S DNA after isolation of total DNA from soil and microbial activities measured as CO(2) emission rates were monitored daily for 14 days after addition of grass-clover (GC) or composted manure (CM) into organic versus conventional soils. Similar to our previous findings, AUDPC and density of copiotrophic bacteria oscillated with time. Fluctuations in species richness (S), Shannon diversity index (H), and individual amplicons on DGGE gels were also detected. Oscillations in AUDPC were positively cross-correlated with copiotrophic CFU in all soils. Oscillations in AUDPC were also positively cross-correlated with 19 to 35% of the high-intensity DNA fragments in soils amended with GC but only 2 to 3% of these fragments in CM-amended soils. AUDPC values were negatively cross-correlated with 13 to 17% of the amplicons with low average intensities in CM-amended soils, which were not correlated with densities of copiotrophic CFU. CO(2) emission rates had remarkable variations in the initial 7 days after either of the soil amendments but were not associated with daily changes in AUDPC. The results suggest that infection by P. ultimum is hampered by competition from culturable copiotrophic bacteria and some high-intensity DGGE amplicons, because AUDPC is cross-correlated with these variables at lags of 1 to 4 days. However, negative cross-correlations with low-intensity DNA fragments indicate that P. ultimum infection could also be suppressed by antagonistic bacteria with low densities that may be nonculturable species, especially in CM amended soil. The organic soil generally had lower AUDPC values, higher bacterial diversity, and negative cross-correlations between AUDPC and low-intensity DNA fragments (after CM amendment), indicating that specific bacteria that do not attain high densities may contribute to P. ultimum suppression in organic soils.     

Investigations on the Biological Control of Some Insect Pests in Bolivia

Abstract

Greenhouse experiments were conducted to evaluate the effects of organic amendments and captafol on the parasitic potential of Paecilomyces lilacinus (Thom) Samson against Meloidogyne incognita in sterile field soil. Tomato cv. Moneymaker plants were used as a host. Organic matter from Tagetes minuta L., Ricinus communis L. and Datura strammonium L. stimulated egg parasitism, while the fungicide captafol inhibited it. Galling intensity and the population of juveniles were significantly lower in soils amended with organic matter. However, no significant differences were detected among the different organic additives. The amended soils supported plants with significantly heavier shoots and roots. The implications of these results on the management of root‐knot nematodes are discussed.     

Effect of synthetic and organic soil fertility amendments on southern blight, soil microbial communities, and yield of processing tomatoes

ABSTRACT Soil fertility amendments, including composted cotton-gin trash, swine manure, a rye-vetch green manure, or synthetic fertilizers, were applied to subplots and tillage on bare soil; or tillage followed by surface mulch with wheat straw were applied to main plots to determine the effect on the incidence of southern blight caused by Sclerotium rolfsii, yield of processing tomato, and soil microbial communities. The amendment-tillage interaction was significant in 1997 and disease incidence was 67% in tilled bare soil receiving synthetic fertilizers; whereas disease incidence was 3, 12, and 16% in surface-mulched plots amended with a composted cotton-gin trash, swine manure, or a rye-vetch green manure. The amendment effect was significant in 1998, and disease incidence was 61% in plots receiving synthetic fertilizer and was 23, 44, and 53% in plots receiving cotton-gin trash, swine manure, or rye-vetch green manure, respectively. In 1997, yields were highest in tilled surface-mulched plots amended with synthetic fertilizers, cotton-gin trash, or swine manure, respectively. In 1998, yields were low in all plots and there were no significant differences in yield due to treatment. Propagule densities of antagonistic soil fungi in the genus Trichoderma were highest in soils amended with composted cotton-gin trash or swine manure in both years. Propagule densities of fluorescent pseudomonads in soil were higher in plots amended with organic amendments than with synthetic fertilizers in both years. Propagules densities of enteric bacteria were elevated in soils amended with raw swine manure biosolids in both years. Our research indicates that some organic amendments, such as cotton-gin trash, reduced the incidence of southern blight in processing tomato and also enhanced populations of beneficial soil microbes.     

低分子量有机酸对不同肥力土壤磷素的活化作用

针对石灰性土壤磷素固定累积问题,采用化学浸提方法,探讨低分子有机酸对不同肥力水平土壤磷素的活化作用,提高磷素的有效性.结果表明,对于低肥力和中肥力土壤,相同浓度下有机酸活化土壤磷的能力表现为草酸＞柠檬酸＞苹果酸;对于高肥力土壤,相同浓度下有机酸活化土壤磷的能力为柠檬酸＞草酸＞苹果酸.低浓度对有机骏对土壤磷的活化有抑制作...     

Effects of micro-organisms on the absorption of inorganic nutrients by plants

Micro-organisms concentrated in the rhizosphere can influence the absorption of inorganic nutrients by plants. The effects were investigated by comparing uptake of nutrients in plants grown in the presence and absence of micro-organisms in both water culture and soil. In water culture, at phosphate concentrations below about 1.0 part/million competition occurs between barley plants and a microflora of casual laboratory contaminants resulting in reduced absorption and translocation of phosphate. In the presence of micro-organisms nitrogen uptake from nitrate was increased and from ammonium ions decreased; uptake of metal from solutions of ferric, zinc and manganous salts and EDTA chelates was enhanced. The results for plants grown in specific soils confirmed that competition from micro-organisms can reduce uptake of phosphate and molybdenum by the plants. The direct effect of rhizosphere micro-organisms can be demonstrated only in special circumstances but such studies aid our understanding of plant nutrition.     

Effects of moisture and carbonate additions on CO_2 emission from calcareous soil during closed–jar incubation

Calcareous soil contains organic and inorganic carbon(C) pools,which both contribute to CO2 emission during closed-jar incubation. The mineralization of organic C and dissolution of inorganic C are both related to soil moisture,but the exact effect of water content on CO2 emission from calcareous soil is unclear. The objective of this experiment was to determine the effect of soil water content(air-dried,30%,70%,and 100% water-holding capacity(WHC)),carbonate type(CaCO3 or MgCO3),and carbonate amount(0.0,1.0%,and 2.0%) on CO2 emission from calcareous soil during closed-jar incubation. Soil CO2 emission increased significantly as the water content increased to 70% WHC,regardless of whether or not the soil was amended with carbonates. Soil CO2 emission remained the same or increased slowly as the soil water content increased from 70% WHC to 100% WHC. When the water content was ≤30% WHC,soil CO2 emission from soil amended with 1.0% inorganic C was greater than that from unamended soil. When the soil water content was 70% or 100% WHC,CO2 emission from CaCO3 amended soil was greater than that from the control. Furthermore,CO2 emission from soil amended with 2.0% CaCO3 was greater than that from soil amended with 1.0% CaCO3. Soil CO2 emission was higher in the MgCO3 amended soil than from the unamended soil. Soil CO2 emission decreased as the MgCO3 content increased. Cumulative CO2 emission was 3-6 times higher from MgCO3 amended soil than from CaCO3 amended soil. There was significant interaction effect between soil moisture and carbonates on CO2 emission. Soil moisture plays an important role in CO2 emission from calcareous soil because it affects both biotic and abiotic processes during the closed-jar incubation.     

小麦根际pH,细菌数量,有机质变化研究

通过研究灰漠上和碱化灰漠上中小麦根际、非根际pH、细菌数量和有机质含量变化,发现两种土壤小麦根际上中细菌数量和有机质含量比非根际上中高。由于较低的pH值,因而灰漠土中小麦根际、非极际土中的有机质含量和细菌数量均高于碱化灰漠土中。