Effects of the construction of fertile and cultivated soil layer on soil fertility and maize yield in Albic soil.

We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm-2·a-1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

Long-term application of fertilizer and manures affect P fractions in Mollisol.

Application of phosphorus (P), a major plant nutrient, as fertilizer is critical to maintain P level for crop production and yield in most cultivated soils. While, it may impact the dynamics, limited studies have examined the long-term effects of fertilization on P fractions in a soil profile in Mollisol. A long-term field experiment was conducted at the State Key Experimental Station of Agroecology of the Chinese Academy of Sciences in Hailun county, Heilongjiang Province, China. A sequential fractionation procedure was used to determine the effect of fertilizer (types) treatments including no fertilizer (CK), chemical fertilizer (NPK), chemical fertilizer plus straw (NPK + S) and pig manure (OM) on fractions of P and their distribution within 0-100 cm soil profiles. Unlike CK treatment, the long-term application of fertilizers increased the concentration and accumulation of total and available P in 0-20 and 0-40 cm soil depths than deeper soils, respectively. The phosphorus activity coefficient (PAC) ranged from 1.5 to 13.8% within 0-100 cm soil depth. The largest PAC value was observed under OM treatment at 0-40 cm soil depth and under NPK + S treatment at 40-100 cm soil depth. The Ca2-P and Ca8-P concentrations increased significantly by 0.5-7.5 times and 0.5-10.4 times, respectively in OM treatment with the largest value in 0-40 cm soil depth over CK treatment. The Al-P concentration under NPK + S and OM treatments increased throughout the soil profile. The OM treatment increased all Po concentrations in the 0-40 cm soil depth, while NPK and NPK + S treatments increased labile organic P, moderately labile organic P, and highly stable organic P in the 0-20 cm soil depth. Thus, the application of fertilizer and straw, or organic manure may enhance inorganic and organic P pool in a Mollisol in Northeast China. Thus, organic manure application in the subsoil as a potential P source and their impact should be considered in developing management practices and policies regarding nutrient management.

[Characteristics of soil fertility during soil fertilization from parent material of a Mollisol in Northeast China]. / 东北黑土成土母质培肥过程中土壤肥力变化特征.

Based on a long-term field experiment located in the central region of Mollisol in Northeast China, we examined the changes of soil fertility and nutrient supply capacity of the newly-formed soils with pot experiment after 14-year different agricultural management practices from parent material (PM) (down to 2.0-3.0 m depth) of a Mollisol, and finally tried to optimize pre-ferential agricultural practices improving soil fertility of seriously eroded PM. After 14-year different agricultural practices, soil organic carbon, total nitrogen, stability of soil aggregate and other rela-ted soil nutrient contents improved compared with PM. Soil fertility level of the newly-developed soils significantly affected nutrient supply capacity for wheat in the pot experiment. Results from principal component analysis showed that soil fertility developed toward to the surface Mollisol after 14 years of different agricultural practices from PM. Surface soils with higher organic carbon inputs in arable soil with chemical fertilizer plus all aboveground biomass incorporated and those in no-tilled alfalfa soil were much approached to surface Mollisol, followed by arable soil with fixed amount of organic inputs and natural fallow soil, while soils without and with only chemical fertilizer were much closed to PM. Our results indicated that 14-year organic carbon inputs improved soil aggregate structure and the decomposition of organic carbon entering into soil, changed soil physical and biochemical properties, and hence caused maturing of soil fertility of PM. Straw returning, organic manure application, and planting alfalfa were recommended for improving soil fertility of eroded soil. These findings would give a better scientific basis for high-efficient fertilization and management practices in eroded Mollisol region.

[Effects of the construction of fertile and cultivated upland soil layer on soil fertility and maize yield in black soil region in Northeast China.] / 肥沃耕层构建对东北黑土区旱地土壤肥力和玉米产量的影响.

Organic amendment return could enhance soil fertility, improve soil structure, and increase crop yield. However, how construction of soil layers can affect soil fertility and crop yield are not fully understood. We examined the effects of constructions of fertile and cultivated soil layer on soil fertility and maize yield in the upland black soil region in Northeast China, to provide theoretical guidance in increasing soil fertility and sustainable development of agriculture. Based on the combination of field plot experiments and demonstration regions, nine study sites with different ecological characteristics were selected from Heilongjiang, Jilin and Liaoning provinces from northeast China, covering dark brown, black, meadow, chernozem, albic, brown and cinnamon soils. There were three treatments in each study site, including maize straw return within 0-35 cm soil layer (CFⅠ), the combination of maize straw and organic manure return within 0-35 cm soil layer (CFⅡ) and conventional agricultural practice without organic amendmentas control (CK). The rate of straw return in CFⅠ and CFⅡ treatments were 10000 kg·hm-2, and full straw for demonstration regions. The rate of organic manure in CFⅡ treatment was 30000 kg·hm-2. Considerable difference in soil fertility were recorded among the nine study sites with the trend of tillage layer > sub-tillage layer, especially for dark brown soil and albic soil. Soil fertility of tillage layer and sub-tillage layer was relatively low both for brown soil and cinnamon soil. The heavy clay and plow pan were pivotal limiting factors of soil fertility for the black soil and the meadow soil. Compared with CK, the concentrations of soil organic matter (SOM), available nitrogen (AN), available phosphorous (AP), and available potassium (AK) in tillage layers was increased on average by 1.85 g·kg-1, 20.16 mg·kg-1, 1.56 mg·kg-1 and 17.2 mg·kg-1 in the CFⅠ and CFⅡ treatments in five study sites with more than two years of treatments. The contents of SOM, AN, AP and AK in sub-tillage layer increased by 2.09 g·kg-1, 12.06 mg·kg-1, 2.18 mg·kg-1 and 3.84 mg·kg-1, compared with tillage layer. CFⅠ treatment significantly enhanced the contents of SOM and AP in both tested soil layers, while CFⅡ treatment significantly enhanced all fertility indices in both tested soil layers. This indicated that the increase of organic amendment return is an effective way to improve soil fertility. Maize yield fluctuated under the combined effect of climatic conditions and soil types. The significant differences in maize yield under CK, CFⅠ and CFⅡ treatments were observed with a trend of CFⅡ > CFⅠ > CK. This result indicated that the construction of fertile and cultivated soil layer could significantly increase maize yield independent of soil types. The construction of fertile and cultivated soil layer based on maize straw return or maize straw and organic manure combined return within 0-35 cm soil layer, could simultaneously increase soil fertility in both tillage and sub-tillage layer, as well as maize yield. We suggested that the selection of approaches of the constructions of fertile and cultivated soil layer should consider soil types and the sources of organic amendments. It should also give priority to soil layers rich in organic manure source to construct fertile and cultivated soil layers.

Labile and recalcitrant components of organic matter of a Mollisol changed with land use and plant litter management: An advanced 13C NMR study.

Soil organic matter (SOM) changes with land use and soil management, yet the controlling factors over the chemical composition of SOM are not fully understood. We applied quantitative 13C nuclear magnetic resonance and spectral editing techniques to measure chemical structures of SOM from different land use types. The land use types included a native grassland (nGL), a crop land with straw burning in the field (bCL), a restored grassland (rGL) and a cropland with straw removed out of the field (rCL) for 28years. The abundances of OCH groups from carbohydrates were higher in the SOMs of the nGL and rGL than in those of the rCL and bCL, while the abundances of OCH3 and aromatic CO groups from lignin were higher in the SOMs of the three-ever cultivated lands (rGL, rCL and bCL) than in that of the nGL. Although aromatic CC groups were most dominant in the Mollisols, they did not consistently decrease after the burnings of straw were ceased in the fields of the rCL and rGL compared to the bCL with continuous burning. In addition, the COO groups were bound with the aromatic CC groups in all the land use types, and the sizes of the aromatic clusters were affected by the land use types. The labile and recalcitrant components were correlated with SOC contents the mineral-associated and particular SOM in a contrasting way. Our results suggested that the chemical composition of SOM in the Mollisol depended on land use types, and that labile and recalcitrant components might be protected through mineral associations and aggregation, respectively. The most abundant aromatics in the Mollisols might not just be pyrogenic and could be oxidized to different extents, depending on field drainage conditions.

Agrobacterium salinitolerans sp. nov., a saline-alkaline-tolerant bacterium isolated from root nodule of Sesbania cannabina.

Two Gram-staining-negative, aerobic bacteria (YIC 5082T and YIC4104) isolated from root nodules of Sesbania cannabina grown in a high-salt and alkaline environment were identified as a group in the genus Agrobacterium because they shared 100 and 99.7 % sequence similarities of 16S rRNA and recA+atpD genes, respectively. These two strains showed 99.2/100 % and 93.9/95.4 % 16S rRNA and recA+atpD gene sequence similarities to Agrobacterium radiobacter LMG140T and Agrobacterium. pusense NRCPB10T, respectively. The average nucleotide identities (ANI) of genome sequences were 89.95 % or lower between YIC 5082T and the species of the genus Agrobacterium examined. Moreover, these two test strains formed a unique nifH lineage deeply separated from other rhizobia. Although the nodC gene was not detected in YIC 5082T and YIC4104, they could form effective root nodules on S. cannabina plants. The main cellular fatty acids in YIC 5082T were summed feature 8 (C18 : 1ω7c/C18 : 1ω6c), C19 : 0cyclo ω8c, summed feature 2 (C12 : 0 aldehyde/unknown equivalent chain length 10.9525) and C16 : 0. The DNA G+C content of YIC 5082T was 59.3 mol%. The failure to utilize d-sorbitol as a carbon source distinguished YIC 5082T from the type strains of related species. YIC 5082T could grow in presence of 5.0 % (w/v) NaCl and at a pH of up to 10.0. Based on results regarding the genetic and phenotypic properties of YIC 5082T and YIC4104 the name Agrobacterium salinitolerans sp. nov. is proposed and YIC 5082T (=HAMBI 3646T=LMG 29287T) is designed as the type strain.

Agrobacterium deltaense sp. nov., an endophytic bacteria isolated from nodule of Sesbania cannabina.

A Gram-negative, non-spore-forming, aerobic rods, strain YIC4121T, was isolated from root nodule of Sesbania cannabina grown in Dongying (Yellow River Delta), Shandong Province, PR China. Based on phylogenetic analysis of 16 S rRNA gene sequences, strain YIC4121T was assigned to the genus Agrobacterium with 99.7, 99.3, 99.0, 98.8 and 98.7% sequence similarities to Agrobacterium radiobacter LMG140T, A. pusense NRCPB10T, A. arsenijevicii KFB 330T, A. nepotum 39/7T and A. larrymoorei ATCC51759T. Analysis of the concatenated housekeeping genes (recA-atpD-glnII), showed lower sequence similarities (≤94.6%) between strain YIC4121T and other recognized Agrobacterium species. Strain YIC4121T shared whole-genome average nucleotide identities (ANI) 87.94, 91.27 and 77.42%, with A. pusense NRCPB10T, A. radiobacter LMG140T and A. larrymoorei ATCC51759T. The predominant cellular fatty acids were C19:0 cyclo ω8c, summed feature 2 (C12:0 aldehyde/unknown 10.9525), summed feature 8 (C18:1 ω7c/C18:1 ω6c), C16:0 3 OH and C16:0. The G + C content of strain YIC4121T was 59.80 mol%. Tween 80, lactulose, citric acid, α-ketoglutaric acid, glycyl-L-glutamic acid and 2, 3-butanediol could not be utilized as carbon source, distinguishing strain YIC4121T from the other related species. Based on the distinctly genetic and phenotypic dissimilarity, a novel species Agrobacterium deltaense sp. nov. is proposed with YIC4121T (=HAMBI 3654T = LMG 29283T) as the type strain.

[Effects of straw incorporated to different locations in soil profile on straw humification coefficient and maize yield.] / æ–½å ¥ä¸åŒåœŸå±‚çš„ç§¸ç§†è æ®–åŒ–ç‰¹å¾åŠå¯¹çŽ‰ç±³äº§é‡çš„å½±å“.

Tillage and straw incorporation are important agricultural practices that can break plough layer and improve black soil fertility. The effects of tillage and straw incorporation on straw humification coefficient, soil organic carbon (SOC), and maize yield were investigated in a field experiment. Subsoil combined with straw incorporation in 20-35 cm soil layer (ST+S) could break plough layer and decrease the bulk density by 5.7%, 3.3% and 5.7% compared with traditional til-lage (TT), subsoil (ST) and traditional tillage combined with straw incorporation (TT+S) in six experimental years, respectively, and the best effects were observed in ST and ST+S treatments in the first expe-rimental year. The rate of straw decomposition was higher in 0-20 cm (72.0%) than in 20-35 cm (59.2%), and the straw humification coefficient in 0-20 cm and 20-35 cm soil la-yers reached the peak in first experimental year with 15.9% and 12.7%, respectively. Compared with initial soil sample, SOC and light fraction organic carbon (LFOC) of TT, ST and ST+S treatments in 0-20 cm soil layer was decreased in experimental years, but was increased by 2.9% and 12.4% within TT+S, respectively. SOC and light fraction organic carbon (LFOC) of ST+S in 20-35 cm soil layer was increased by 9.2% and 9.9%, respectively. The effect of field treatments on maize yield showed in a decreasing trend of ST+S>TT+S>ST>TT, effects of tillage and straw incorporation on maize yield could continue 3 and 6 years, respectively, indicating that tillage and straw incorporation had time effect. Therefore, straw incorporated into 20-35 cm soil layer based on tillage was an effective, sustainable agricultural practice of improving black soil quality.

Rhizobium hidalgonense sp. nov., a nodule endophytic bacterium of Phaseolus vulgaris in acid soil.

One Gram-negative, aerobic, motile, rod-shaped bacterium, designated as FH14T, was isolated from nodules of Phaseolus vulgaris grown in Hidalgo State of Mexico. Results based upon 16S rRNA gene (≥99.8 % similarities to known species), concatenated sequence (recA, atpD and glnII) analysis of three housekeeping genes (≤93.4 % similarities to known species) and average nucleotide identity (ANI) values of genome sequence (ranged from 87.6 to 90.0 % to related species) indicated the distinct position of strain FH14T within the genus Rhizobium. In analyses of symbiotic genes, only nitrogen fixation gene nifH was amplified that had nucleotide sequence identical to those of the bean-nodulating strains in R. phaseoli and R. vallis, while nodulation gene nodC gene was not amplified. The failure of nodulation to its original host P. vulgaris and other legumes evidenced the loss of its nodulation capability. Strain FH14T contained summed feature 8 (C18:1 ω6c/C18:1 ω7c, 59.96 %), C16:0 (10.6 %) and summed feature 2 (C12:0 aldehyde/unknown 10.928, 10.24 %) as the major components of cellular fatty acids. Failure to utilize alaninamide, and utilizing L-alanine, L-asparagine and γ-amino butyric acid as carbon source, distinguished the strain FH14T from the type strains for the related species. The genome size and DNA G+C content of FH14T were 6.94 Mbp and 60.8 mol %, respectively. Based on those results, a novel specie in Rhizobium, named Rhizobium hidalgonense sp. nov., was proposed, with FH14T (=HAMBI 3636T = LMG 29288T) as the type strain.

Change in soil organic carbon between 1981 and 2011 in croplands of Heilongjiang Province, northeast China.

BACKGROUND: Soil organic carbon (SOC) is fundamental for mitigating climate change as well as improving soil fertility. Databases of SOC obtained from soil surveys in 1981 and 2011 were used to assess SOC change (0-20 cm) in croplands of Heilongjiang Province in northeast China. Three counties (Lindian, Hailun and Baoqing) were selected as typical croplands representing major soil types and land use types in the region. RESULTS: The changes in SOC density (SOCD) between 1981 and 2001 were -6.6, -14.7 and 5.7 Mg C ha(-1) in Lindian, Hailun and Baoqing Counties respectively. The total SOC storage (SOCS) changes were estimated to be -11.3, -19.1 and 16.5% of those in 1981 in the respective counties. The results showed 22-550% increases in SOCS in rice (Oryza sativa L.) paddies in the three counties, but 28-33% decreases in dry cropland in Lindian and Hailun Counties. In addition, an increase of 11.4 Mg C ha(-1) in SOCD was observed in state-owned farms (P < 0.05), whereas no significant change was observed in family-owned farms. CONCLUSION: Soil C:N ratio and initial SOCD related to soil groups were important determinants of SOCD changes. Land use and residue returning greatly affected SOC changes in the study region. To increase the topsoil SOCD, the results suggest the conversion of dry croplands to rice paddies and returning of crop residue to soils.

[Profile distribution and storage of soil organic carbon in a black soil as affected by land use types].

Taking soils in a long-term experimental field over 29 years with different land uses types, including arable land, bare land, grassland and larch forest land as test materials, the distribution and storage of soil organic carbon (SOC) in the profile (0-200 cm) in typical black soil (Mollisol) region of China were investigated. The results showed that the most significant differences in SOC content occurred in the 0-10 cm surface soil layer among all soils with the order of grassland > arable land > larch forest land > bare land. SOC contents at 10-120 cm depth were lower in arable land as compared with the other land use types. Compared with arable land, grassland could improve SOC content obviously. SOC content down to a depth of 60 cm in grassland was significantly higher than that in arable land. The content of SOC at 0-10 cm in bare land was significantly lower than that in arable land. Although there were no significant differences in SOC content at 0-20 cm depth between larch forestland and arable land, the SOC contents at 20-140 cm depth were generally higher in larch forestland than that in arable land. In general, SOC content showed a significantly negative relationship with soil pH, bulk density, silt and clay content and an even stronger significantly positive relationship with soil total N content and sand content. The SOC storage in arable land at 0-200 cm depth was significantly lower than that in the other three land use types, which was 13.6%, 11.4% and 10.9% lower than in grassland, bare land and larch forest land, respectively. Therefore, the arable land of black soil has a great potential for sequestering C in soil and improving environmental quality.

Abundance and diversity of soybean-nodulating rhizobia in black soil are impacted by land use and crop management.

To investigate the effects of land use and crop management on soybean rhizobial communities, 280 nodule isolates were trapped from 7 fields with different land use and culture histories. Besides the known Bradyrhizobium japonicum, three novel genospecies were isolated from these fields. Grassland (GL) maintained a higher diversity of soybean bradyrhizobia than the other cultivation systems. Two genospecies (Bradyrhizobium spp. I and III) were distributed widely in all treatments, while Bradyrhizobium sp. II was found only in GL treatment. Cultivation with soybeans increased the rhizobial abundance and diversity, except for the soybean monoculture (S-S) treatment. In monoculture systems, soybeans favored Bradyrhizobium sp. I, while maize and wheat favored Bradyrhizobium sp. III. Fertilization decreased the rhizobial diversity indexes but did not change the species composition. The organic carbon (OC) and available phosphorus (AP) contents and pH were the main soil parameters positively correlated with the distribution of Bradyrhizobium spp. I and II and Bradyrhizobium japonicum and negatively correlated with Bradyrhizobium sp. III. These results revealed that different land uses and crop management could not only alter the diversity and abundance of soybean rhizobia, but also change interactions between rhizobia and legume or nonlegume plants, which offered novel information about the biogeography of rhizobia.

Nitrous oxide emissions from Mollisols as affected by long-term applications of organic amendments and chemical fertilizers.

A field experiment was conducted to evaluate the influences of long-term applications of organic amendments and chemical fertilizers on nitrous oxide (N2O) emissions from Mollisols in northeast China and to relate soil N2O fluxes to soil moisture and temperature. A closed-chamber method was used to determine soil N2O flux during the maize growing season in 2011. In the entire maize growing period, cumulative N2O emissions were significantly (all P<0.05) increased by 66, 86 and 83% under the applications of 4.5 Mg ha(-1) maize straw combined with NPK, 7.5 and 22.5 Mg ha(-1) pig manure combined with NPK, respectively, compared with the control (0.64±0.01 kg N2O-N ha(-1)), whereas NPK fertilizer alone and 2.25 Mg ha(-1) maize straw combined with NPK had no remarkable influences (P>0.05). Nonetheless, even increasing nitrogen inputs, the cumulative microbial N2O emission over 126 days had an upper threshold around 1.2 kg N2O-N ha(-1). Approximately 25-44% of N2O was emitted from the applied organic amendments, and the emission factor (EF) of applied organic amendments as N2O based on 126 days was between 0.07 and 1.52%, higher than NPK fertilizer-induced EF (0.03%). Soil temperature explained 38-96% of the seasonal variation in soil N2O fluxes using exponential models, with a Q10 of 2.01-3.48. Our results suggest that the influences of organic amendments on soil N2O emissions from Mollisols primarily vary with the type of the applied organic amendments, whereas great nitrogen inputs at maximum asymptotically double baseline cumulative emissions.

[Long-term fertilization on the behavior of aging of the phenanthrene in the black soil aggregates].

The soil samples were collected from the surface (0-20 cm) soil of the long-term fertilizer experiments in black soil areas in Northeast Location Monitoring Field [fertilizers and organic fertilizers (NPOM), no fertilization (NF)], and indoor culture method was adopted to study the behaviour of aging of the phenanthrene different size of soil aggregates and its contributing factors of aging source analysis. The results show that in the beginning of the aging > 2 mm aggregate fraction was a priority adsorbent, while last stage of the aging < 0.053 mm aggregate fraction was the preferred adsorbent. In the 120-day aging period, the extraction rate of 0.25-0.053 mm and 0.25-2 mm aggregate fraction had no significant difference. The phenanthrene residual content in undisturbed soil of NPOM treatment was 31.13%, while in the NF treatment residual content of undisturbed soil was 27.73%. Average rates of the phenanthrene aging in the NPOM and NF treatments was 0.26% x d(-1) and 0.23% x d(-1). The five major influence factors of the combination of content of the residual phenanthrene based on principal component analysis were analyzed, the results showed that the organic carbon and specific surface area were the mainly factors combined with residual content of phenanthrene. As a consequence, Long-term application of fertilizers was in favour of the aging behaviour of phenanthrene, thereby reducing the activity and toxicity of phenanthrene in the black soil.

[Effects of low molecular organic acids on nitrogen accumulation, nodulation, and nitrogen fixation of soybean (Glycine max L.) under phosphorus deficiency stress].

A greenhouse sand culture experiment was conducted to study the effects of citric acid, oxalic acid, malic acid, and their mixture on the nitrogen accumulation, nodulation, and nitrogen fixation of soybean. After the application of test low molecular weight organic acids, the nitrogen accumulation in the aboveground part of soybean decreased by 17.6%-44.9% at seedling stage, 29.8%-88.4% at flowering stage, 9.18%-69.6% at podding stage, and 2.21%-41.7% at maturing stage). In the meanwhile, the nodule number, nitrogenase activity, and leghemoglobin content decreased by 11.4%-59.6%, 80.5%-91.7%, and 11.9%-59.9%, respectively, resulting in a significant decrease (9.71%-64.5%) of nitrogen fixation of soybean, compared with the control. The inhibitory effect of test low molecular weight organic acids increased with their increasing concentration. Oxalic acid had a higher inhibitory effect than citric acid and malic acid, and the mixture of the three organic acids had an enhanced inhibitory effect.

[Construction effect of fertile cultivated layer in black soil].

The clayey farmland soil in black soil region of Northeast China, due to the existence of thicker plough pan created by unreasonable tillage, is a main limiting factor for local agricultural production. In this paper, a field experiment was conducted to study the construction effect of fertile cultivated layer on crop yield, soil physical properties, soil moisture content, and soil microbial number. After the construction of fertile cultivated layer, the soil had a thicker cultivated layer, and the crop yield was increased. Comparing with traditional tillage, applying straw and organic manure into 20-35 cm soil layer decreased soil bulk density by 9.88% and 6.20%, increased soil porosity by 9.58% and 6.02%, and enhanced soil saturated hydraulic conductivity by 167.99 and 73.78%, respectively, indicating that the construction of fertile cultivated layer could improve soil aeration and water permeability, and enhance the infiltration of rainfall. The soil moisture content and water use efficiency under the application of straw and organic manure into plough pan were higher than those under traditional tillage, and a positive correlation was observed between the moisture content in 0-35 cm soil layer and the emergence of maize seedlings. Due to the increased organic carbon source and aeration in the constructed fertile cultivated layer, soil microbial number was also increased.

[Influence of soluble carbon and nitrogen on ammonia volatilization from different thermal zones soil].

A static absorption method was used to study the influence of soluble carbon and nitrogen on ammonia volatilization from different thermal zone soils, such as black soil, red soil and cinnamon soil, performed in laboratory. Results showed that nitrogen application enhanced ammonia volatilization significantly. The amount of ammonia volatilization in cinnamon soil ranged from 14.3 to 7.37 mg x kg(-1), which in black soil from 1.52 to 1.11 mg x kg(-1) and from 0.998 to 0.402 mg x kg(-1) in red soil applied with only nitrogen or nitrogen amended with soluble carbon. Moreover, soluble carbon decreased ammonia volatilization caused by nitrogen, and amounts of decrease were 27.0%, 48.5%, 60.0% in black soil, cinnamon soil and red soil separately. The amount of ammonia volatilization from black soil and cinnamon soil applied only nitrogen was in an order of CK > NPK > NPKOM, while contrary order appeared if nitrogen was amended with soluble carbon. However, it was the same order for red soil applied with only nitrogen or nitrogen amended with soluble carbon. In addition, the variances of NH4+ -N and NO3- -N contents in cinnamon soil were larger than other soils, which suggested that cinnamon soil had high potential of nitrogen loss.

[Effects of long-term fertilization on enzyme activities in black soil of Northeast China].

In this paper, black soil samples at the depths of 0-20 cm and 20-40 cm were collected from the Hailun Agricultural Ecology Station of Chinese Academy of Sciences to study the effects of long-term fertilization on their urease, invertase, phosphatase and catalase activities and total C and N contents. The results showed that long-term application of chemical fertilizers and organic manure increased the activities of urease, invertase and phosphatase in 0-20 cm and 20-40 cm soil layers in different degree, and the combined application of them increased the activities of the three enzymes significantly, with an increment of 43.6%-113.2%, 25.9%-79.5% and 14.7%-134.4% in 0-20 cm soil layer and 56.1%-127.2%, 14.5%-113.8% and 16.2%-207.2% in 20-40 cm soil layer, respectively. However, long-term application of chemical fertilizers without organic manure had little effects on catalase activity. The activities of urease, invertase and phosphatase decreased with increasing soil depth. Long-term application of N fertilizer increased urease activity, and P fertilization had obvious positive effect on phosphatase activity. Long-term fertilization also had obvious effects on the soil total C and N contents and C/N ratio.

[Cadmium accumulation and its development tendency in black soil under long-term fertilization].

Based on the long-term field experiment at Hailun Agro-ecosystem Experimental Station of Chinese Academy of Sciences, this paper studied the cadmium (Cd) accumulation, its development tendency, and Cd availability in black soil under effects of long-term application of chemical N and P fertilizers and pig manure. The results showed that under no fertilization, soil Cd concentration had a slight increase. Long-term chemical N and P fertilization increased soil Cd concentration significantly, but soil Cd accumulation had less difference under different N and P fertilization rates. Applying pig manure increased the Cd accumulation in soil significantly, and the accumulation had a tendency of speed-up. Cd-containing feedstuff additives could be the important source of Cd in pig manure. No significant effects of chemical N and P fertilization were observed on the Cd availability in soil, but long-term application of pig manure increased the Cd availability significantly.

[Effects of different land management practices on black soil microbial biomass C and enzyme activities].

In a long-term experimental plot at the Hailun Agricultural Ecology Station of Chinese Academy of Sciences in Heilongjiang Province, Northeast China, the effects of three land management practices including natural restoration, fallowing and cropping on black soil microbial biomass C and enzyme activities at the depths of 0-10, 20-30 and 40-50 cm were investigated. The results showed that at 0-10 cm, soil microbial biomass C and soil urease, phosphatase, catalase and invertase activities were in the sequence of natural restoration > cropping > fallowing, while at 20-30 cm and 40-50 cm, they had less significant differences as those at 0-10 cm. Under natural restoration and cropping, soil microbial biomass C and soil urease, phosphatase and catalase activities decreased with increasing soil depth, while under fallowing, they were higher at 20-30 cm. Correlation analysis showed that there existed significant positive correlations between soil total C and total N, soil total C and microbial biomass C, and soil microbial biomass C and test enzyme activities. The indices soil microbial biomass C and soil enzyme activities showed that black soil under long-term natural restoration had better soil quality.