Impact of wetting-drying cycles and acidic conditions on the soil aggregate stability of yellow‒brown soil

Soil aggregate is the basic structural unit of soil,which is the foundation for supporting ecosystem functions,while its composition and stability is significantly affected by the external environment.This study was conducted to explore the effect of external environment(wetting-drying cycles and acidic conditions)on the soil aggregate distribution and stability and identify the key soil physicochemical factors that affect the soil aggregate stability.The yellow‒brown soil from the Three Gorges Reservoir area(TGRA)was used,and 8 wetting-drying conditions(0,1,2,3,4,5,10 and 15 cycles)were simulated under 4 acidic conditions(pH=3,4,5 and 7).The particle size distribution and soil aggregate stability were determined by wet sieving method,the contribution of environmental factors(acid condition,wetting-drying cycle and their combined action)to the soil aggregate stability was clarified and the key soil physicochemical factors that affect the soil aggregate stability under wetting-drying cycles and acidic conditions were determined by using the Pearson’s correlation analysis,Partial least squares path modeling(PLS‒PM)and multiple linear regression analysis.The results indicate that wetting-drying cycles and acidic conditions have significant effects on the stability of soil aggregates,the soil aggregate stability gradually decreases with increasing number of wetting-drying cycles and it obviously decreases with the increase of acidity.Moreover,the combination of wetting-drying cycles and acidic conditions aggravate the reduction in the soil aggregate stability.The wetting-drying cycles,acidic conditions and their combined effect imposes significant impact on the soil aggregate stability,and the wetting-drying cycles exert the greatest influence.The soil aggregate stability is significantly correlated with the pH,Ca^(2+),Mg^(2+),maximum disintegration index(MDI)and soil bulk density(SBD).The PLS‒PM and multiple linear regression analysis further reveal that the soil aggregate stability is primarily influenced by SBD,Ca^(2+),and MDI.These results offer a scientific basis for understanding the soil aggregate breakdown mechanism and are helpful for clarifying the coupled effect of wetting-drying cycles and acid rain on terrestrial ecosystems in the TGRA.

Vertical variation and storage of nitrogen in an aquic brown soil under different land uses

The vertical variation and storage of nitrogen in the depth of 0-150 cm of an aquic brown soil were studied under 14 years of four land use patterns, i.e., paddy field, maize field, fallow field and woodland in Shenyang Experimental Station of Ecology, Chinese Academy of Sciences in November of 2003. The results showed that different land uses had different profile distributions of soil total nitrogen (STN), alkali N, ammonium (NH4+-N) and nitrate (NO3--N). The sequence of STN storage was woodland >maize field > fallow field > paddy field, while that of NO3--N content was maize field > paddy field > woodland > fallow field, suggesting the different root biomass and biological N cycling under various land uses. The STN storage in the depth of 0-100 cm of woodland averaged to 11.41 thm-1, being 1.65 and 1.25 times as much as that in paddy and maize fields, respec-tively, while there was no significant difference between maize and fallow fields. The comparatively higher amount of NO3--N in maize and paddy fields may be due to nitrogen fertilization and anthropogenic disturbance. Soil alkali N was significantly related with STN, and the correlation could be expressed by a linear regression model under each land use (R20.929, p<0.001). Such a correlation was slightly closer in nature (woodland and fallow field) than in agro ecosystems (paddy and maize fields). Heavy N fertilization induced an excess of crop need, and led to a comparatively higher amount of soil NO3--N in cultivated fields than in fallow field and woodland. It is suggested that agroforestry practices have the potential to make a significant contribution to both crop production and environment protection.

Influence of Dark Brown Soil Respiration and Microbial Community under Cadmium Stress

Through laboratory simulation, the influence of cadmium on soil respiratory intensity and microbial community were studied by adding different concentrations of heavy metal cadmium. The results indicated that, the soil respiration had a signifi- cant weakening trend in the same culture days with increasing exogenous cadmium content; the soil respiration intensity was decreased obviously with the increase of culture time, especially after 14 d when the soil exogenous cadmium content was in the range of 0.5-3.0 mg/kg, while the soil respiration had not obvious variation over time when the exogenous cadmium content was in the range of 5.0-10.0 mg/kg. The soil microbial communities decreased significantly and were much lower than that of the control treatment in the same culture days with the increasing of soil exogenous cadmium content; the soil microbial community declined significantly with increasing of culture time for all exogenous cadmium treatments. The number of soil microbial communities in treatment with 10 mg/kg of exogenous cadmium were only 46.43%, 32.26%, 28.74%, 27.39% and 24.62% of that in control treatment on the 7th, 14th, 21st, 28th and 42rd of culture, respectively. It indicated that higher concen- tration of cadmium in dark brown soil had a significant inhibitory effect on soil mi- crobial growth.

A comparison of measured ^(137)Cs and excess ^(210)Pb levels in the cultivated brown and cinnamon soils of the Yimeng Mountain area

This contribution analyzes the similarities and differences between the measured activities of 137Cs and excess 210Pb(210Pbex) in the cultivated brown and cinnamon soils of the Yimeng Mountain area, discusses the influence of soil texture on the measurement of 210Pbex, and presents differences between the two types of soils. Fields A and B were selected to represent the fields that contain cultivated brown and cinnamon soils, respectively. From either study field, one site of sectioned core and six bulk cores were collected to measure 137Cs levels, 210Pbex levels, and the particle-size composition of soil samples. Three undisturbed soil samples were collected to measure capillary and aeration porosities. The 137Cs inventories for the two study fields are very similar. The 137Cs is a man-made radionuclide, which means that its measured levels for soils are unaffected by soil texture. In contrast, levels of the naturally occurring 210Pbex of soils from Field A were lower than those of Field B by about 50%. In contrast to aquatic sediments, levels of 210Pbex in terrestrial surface soils are affected by the emanation of 222Rn from the soils. It can be assumed that the coarser the soils, the greater the emanation of 222Rn; in addition, the lower the measured 210Pbex, the greater the underestimate of this value. The cultivated brown soils in Field A are coarser than the cultivated cinnamon soils in Field B. As a result, 222Rn in Field A will diffuse more easily into the atmosphere than that in Field B. As a consequence, the measured 210Pbex in soils from Field A is much lower than the actual value, whereas the value measured for Field B is much closer to the actual value.

Effects of Exogenous Organic Acids on Phosphorus Availability of Dark Brown Forest Soils and Phosphorus Absorption and Accumulation of Larix olgensis Seedlings with Nutrient Deficiency

Different proportions of A1 and B horizons dark brown forest soils （A1∶B=1∶2） were utilized to set the soil nutrient deficient conditions, and Larix olgensis seedlings were cultivated. By simulating organic acids concentrations in forest litter leachates of northeast China, the effects and mechanism of different concentrations of organic acid solutions on phosphorus （P） availability of dark brown forest soils and P absorption of Larix olgensis seedlings with nutrient deficiency were studied. The results showed that, compared with A1 horizon soils, available P contents of mixed soils in A1 and B horizons decreased, and P accumulation and efficiency of P uptake in root and leaves of Larix olgensis seedlings also decreased, but efficiency of P utilization increased. After treatments of exogenous organic acids, available P contents of mixed soils increased and the impact sequence of different organic acids were succinic acid 〉 citric acid 〉 oxalic acid; the concentration of 5.0 mmol/L had the best function, and the best effect of organic acids was at 20 d. Organic acids also increased P accumulation and efficiency of P uptake in roots and leaves of Larix olgensis seedlings, but decreased efficiency of P utilization. The impact strength of organic acids on P accumulation and efficiency of P uptake varied with treatment time, type and concentration of organic acids. The results of 20 d and 30 d in roots were higher than those of 10 d, however, the results of 10 d and 20 d in leaves were higher than those of 30 d, thus, at the earlier stage of organic acids treatments, more P absorbed were transferred to leaves, and at the later stage, more P would be accumulated in roots. The concentration of 10.0 mmol/L had the best function, and the impact sequence of different organic acids was succinic acid 〉 citric acid 〉 oxalic acid. Therefore, organic acids might contribute to P absorption and accumulation by Larix olgensis seedlings, final y increasing the adaptability and endurance of Larix olgensis seedlings to nutrient deficient soils.

Effects of Fertilization Patterns on Chemical Forms of Nitrogen in Dark Brown Soil and Its Distribution in Different Aggregates

[Objective] This study was conducted to investigate the effects of tradition-al fertilization and formula fertilization by soil testing on the chemical forms of nitro-gen in dark brown soil and its distribution in different aggregates. [Method] A physi-co-chemistry method was adopted in a comparative study on the chemical forms of nitrogen and their distribution in different-sized aggregates of dark brown soil under traditional fertilization and formula fertilization by soil testing respectively. [Result] Compared with traditional fertilization in spring and autumn, the formula fertilization by soil testing averagely decreased, the total nitrogen in soil by 23.2% in spring and by 20% in autumn in the soil layer of 0-20 cm, by 48.8% in the layer of 20-40 cm. Ammonium nitrogen was so sensitive to the methods of fertilization that the content of ammonium nitrogen was reduced much more under formula fertitization by soil testing in autumn than under traditional fertilization. Nitrogen in soil under traditional fertilization pattern was mainly distributed in the aggregates of 0-0.25 and 0.5-1 mm, while in formula fertilization by soil testing it was mainly distributed in the aggregates of 0.25-0.5 and 0-0.25 mm. [Conclusion] The study proved that for-mula fertilization by soil testing helped to reduce the risk of nitrogen pol ution and had huge effects on the chemical forms and distribution of nitrogen in different ag-gregates in dark brown soil.

Vertical distribution of plant nematodes in an aquic brown soil under different land uses

The vertical distribution of the dominant genera of plant nematodes at the depth of 0–150 cm of an aquic brown soil were studied for four land use patterns, i.e., paddy field, maize field, fallow field and woodland in the Shenyang Experimental Station of Ecology, Chi- nese Academy of Sciences in November of 2003. The results showed that the numbers of some dominant genera under different land uses decreased with the increase of soil depth. Helicotylenchus was most dominant genus under each land use type. Genera of Filenchus, Psilen- chus and Tylenchus in paddy field occurred at the depth of 0–20 cm; while Paratylenchus in fallow field and woodland, as well as Praty- lenchus in maize field presented in the deeper soil layers (0–80 cm). Significant correlations between the numbers of dominant genera of plant nematodes and soil chemical properties were found in this study. The number of Helicotylenchus under different land uses was posi- tively correlated with C/N ratio, total C, total N, total P, alkai-N, and Olsen-P. The numbers of Filenchus and Paratylenchus in paddy field, Pratylenchus in maize field and Paratylenchus in fallow field were negatively correlated with soil pH, and positively correlated with total C, total N and alkai-N. This study results showed that it is essential to sample at a certain depth according to the vertical distribution informa- tion of different genera of plant nematodes in adequately assessing the population size of plant nematodes.

Profile Distribution and Storage of Soil Organic Carbon in an Aquic BrownSoil as Affected by Land Use

Many attempts have been made to estimate the soil organic carbon (SOC) storage under different land uses, especiallyfrom the conversion of forest land or grassland into cultivated field, but limited reports were found on the estimation ofthis storage after cultivated field converted into woodland or grassland, especially in small scales. This study is aimed toinvestigate the dynamics of SOC concentration, its storage and carbon /nitrogen (C/N) ratio in an aquic brown soil at theShenyang Experimental Station of Ecology, Chinese Academy of Sciences under four land use patterns over 14 years. Thefour land use patterns were paddy field (PF), maize field (MF), fallow field (FF) and woodland (WL). In each pedon at 0-150cm depth, soil samples were collected from ten layers. The results showed that the profile distribution of SOC was differentunder different land uses, indicating the effect of land use on SOC. Soil organic carbon was significantly related with soiltotal N, and the correlation was slightly closer in nature ecosystems (with R2=0.990 and P<0.001 in both WL and FF, n=30)than in agroecosystems (with R2=0.976 and P<0.001 in PF, and R2=0.980 and P<0.001 in MF, n=30). The C/N ratio in theprofiles decreased generally with depth under the four land use patterns, and was comparatively higher in WL and lowerin PF. The C/N ratio of the FF was closer to that in the same soil depths of MF than to that of PF. Within 100 cm depth, theannual sequestration of SOC was 4.25, 2.87, and 4.48 t ha-1 more in WL than in PF, MF and FF, the annual SOC increasingrate being 6.15, 3.26, and 5.09 % higher, respectively. As a result, the SOC storage was significantly greater in WL than inany of the other three land use patterns, P=0.001, 0.008, and 0.008 as compared with PF, MF, and FF, respectively, whilethere was no significant difference among the other three land uses. It is suggested that woodland has the potential tomake a significant contribution to C storage and environmental quality.

Effects of red-yellow soil acidification on seed germination of Chinese pine

Acid treatments significantly change the physical and chemical properties of red yellow soil by lowering its pH value and leaching out aluminum(Al) ions that are harmful to the growth of plants. The structure of soil will be damaged, resulting in higher viscosity, higher water retention rate and lower air permeability of the soil. The germination rate of Chinese pine( Pinus tabulacformic Carr. ) seeds sowed in soil treated with sulphuric acid(H 2SO 4) decreased compared to that for untreated soil. The direct cause was the large amount of Al ions leached out because of low pH values(≥3.5). The added acid decreased the soil aggregation and increased the number of micro aggregates(under 250 μm in diameter). Such changes increased the soil's viscosity, which tied the pine needles to the soil after the seeds had germinated and prevented the seedlings from fully developing.

Effects of Long-term Located Fertilization on Wheat Yield and Soil Nutrients of Three Types of Soils in Shandong Province

[Objective] This study aimed to investigate the effects of long-term differ- ent fertilization in three types of soils on wheat yield and soil nutrient variation in Shandong Province. [Method] A 30-year located experiment in Jinan of Shandong Province was selected and the results of soil nutrient and crop yield in 1984, 1987, 1988, 1989, 1990, 2001, 2005, 2006, 2007 and 2010 were measured and collected. In this study, five treatments： CK, NP, NK, PK and NPK of the located experiment were selected. [Result] The three types of soils in wheat yields decreased signifi- cantly in the first several years and in 2006. Wheat yields of the treatments with P fertilizers were obviously higher than those without P fertilizers; it was shown that phosphorus is the primary nutritional factor for high-yielding of wheat. The highest yield is from cinnamon soil, followed by that from brown soil, and the lowest pro- duction is from fluvo-aquic soil. Under the same fertilization, the influence of other factors on wheat yield of brown soil is the smallest, while cinnamon soil is vulnera- ble to the influence of external conditions, resulting in larger fluctuation of annual wheat yield. The alkali-hydro nitrogen contents of three kinds of soils first de- creased, then raised, and at last reduced apparently. Since 2007, the change of al- kali-hydro nitrogen content appeared rebounded. The available P contents of no- phosphorus treatments decreased over time while those of the treatments with P fertilizers increased at first, then decreased, and after that kept relatively stable. The available K contents of no K treatments decreased slowly. The treatments of PK and NK had higher available K content than NPK treatment. [Conclusion] Thus, it is an effective fertilization measure to improve the wheat yield by supplying reasonable phosphate fertilizer and nitrogen fertilizer and making up potassium fertilizer.

Study on Exchangeable Cation Determining Base Saturation Percentage of Soil in South China

Base saturation percentage (BSP) is an important soil chemical index in soil fertility and soil taxonomy. However, it is still unclear what exchangeable cation dominates BSP of soil in south China. Therefore, in this study, the data of BSPs and exchangeable H+, Al3+, Ca2+, Mg2+, K+ and Na+ of 109 and 45 horizon samples of 50 and 28 soil species in red soil and yellow soil groups in the Database of Chinese Soil Species were used to explore further the characteristics of BSPs and exchangeable cations as well as the correlation between BSPs and exchangeable cations. The results showed that the concentrations of exchangeable cations in both red soil and yellow soil groups were in an order of Al3+ (4.55 ± 1.47 and 4.22 ± 1.2 cmol(+)/kg) > Ca2+ (0.32 ± 0.21 and 0.36 ± 0.24 cmol(+)/kg) > H+ (0.23 ± 0.13 and 0.19 ± 0.10 cmol(+)/kg) > K+ (0.16 ± 0.09 and 0.16 ± 0.11 cmol(+)/kg) > Mg2+ (0.13 ± 0.09 and 0.11 ± 0.08 cmol(+)/kg) > Na+ (0.08 ± 0.06 and 0.11 ± 0.06 cmol(+)/kg). For red soil group, Al3+ concentration was significantly higher than those of other exchangeable cations, Ca2+ and H+ concentrations were significantly higher than those of K+, Mg2+ and Na+;while for yellow soil group, Ca2+, H+ and K+ concentrations were significantly higher than those of Mg2+ and K+. BSP of red soil group was codetermined by Ca2+, Al3+, Mg2+ and Na+, with the contributions of 33.81%, 19.82% and 14.49%, respectively;while BSP of yellow soil group was codetermined by Al3+, Ca2+, Mg2+, K+ and Na+, with the contributions of 24.91%, 21.55%, 19.91% and 14.21%, respectively. A higher concentration of exchangeable cation does not mean the higher importance of the cation to soil BSP.

Susceptibility of Wheat Varieties to Soil-Borne <i>Rhizoctonia</i>Infection

Response of 19 wheat varieties cultivated in Hungary varied within large limits to soil borne Rhizoctonia infection. The most frequent symptom, usually leading to damping off was the root neck necrosis. Four significant factors influencing the susceptibility of wheat comprised 71% of total variation but none of them was dominant. The inhibition of development of survivors in Rhizoctonia infested soil correlated with overall susceptibility of variety concerned. The varieties Emese, Kikelet and Palotás are proved to be less susceptible, but none of the varieties could be certified as tolerant. No relationships were revealed between pathogenicity of 26 Rhizoctonia strains studied and their taxonomic position or origin. The anamorph strains of Athelia, Ceratobasidium, Ceratorhiza and Waitea similar to Thanatephorus anamorphs selectively infected the wheat varieties, but the syndromatic pictures were undistinguishable with unarmed eye. R. solani was proved to be more aggressive against germinating wheat than R. cerealis. Nine significant factors influencing the virulence of Rhizoctonia strains comprised 82% of total variation, and six of them influenced exclusively Thanatephorus anamorphs.

岩溶区镉污染棕色石灰土母质稻田土壤团聚体镉赋存特性研究

【目的】研究桂西北岩溶区镉(Cd)污染棕色石灰土母质稻田土壤团聚体Cd赋存形态特性,为区域内该类型Cd污染稻田稻米安全生产提供数据参考。【方法】采用湿筛法将采样土壤团聚体分离成>2.000 mm、1.000~2.000 mm、0.250~1.000 mm、0.074~0.250 mm和<0.074 mm 5个粒级的团聚体,研究桂西北岩溶区0~20、20~30、30~50和50~80 cm剖面深度土壤团聚体粒径组成、不同粒径团聚体Cd含量及其主要赋存形态。【结果】各层剖面0.250~1.000 mm粒径团聚体占比较为稳定,均在30.00%以上,各层剖面间无显著差异(P>0.05)。0~20 cm剖面(耕作层)中>2.000 mm粒径团聚体占比最大(40.20%),随着剖面深度增加,>2.000 mm粒径团聚体占比迅速降低,<0.250 mm粒径团聚体占比呈逐渐增加趋势。不同粒径团聚体Cd含量分析结果表明,在0~20、20~30和30~50 cm剖面中,Cd主要富集在>2.000 mm粒径团聚体中,Cd含量分别高达2.22、1.66和0.95 mg/kg,在50~80 cm剖面中,Cd主要富集在1.000~2.000 mm粒径团聚体中。>2.000 mm粒径团聚体在0~30 cm土层中对全土Cd含量的贡献率最大。不同剖面深度团聚体中Cd赋存形态存在明显差异,0~20 cm剖面各粒径团聚体中Cd主要以有机结合态存在,可交换态Cd占比最小(<0.074 mm粒径团聚体除外),随着剖面深度增加,团聚体中可交换态Cd占比明显增加,当剖面深度增加至30 cm以下时,团聚体中Cd主要以碳酸结合态存在,残渣态含量最小。【结论】桂西北岩溶区Cd污染棕色石灰土母质稻田Cd主要富集在>2.000 mm和1.000~2.000 mm粒径的团聚体中;0~20 cm耕作层各粒径团聚体中的Cd主要以有机结合态存在,可交换态占比最小,随着剖面深度的增加,可交换态Cd占比明显增加,稳定形态Cd占比明显降低。因此,在实际生产过程中要注重提高土壤大粒径团聚体含量,避免过度精耕和深翻,减少耕层土壤可交换态Cd含量,降低水稻生产过程中稻米Cd超标的风险。

不同水分条件下氨基酸添加对温带暗棕壤碳氮含量和甲烷排放的影响

【目的】解析土壤pH值与土壤氮以及CH_(4)排放速率与土壤碳氮含量间的相互关系,为明确碳氮转化及温室气体排放规律、优化温带森林暗棕壤的水分管理提供依据。【方法】以温带森林暗棕壤为研究对象,采用室内培养法,设置水分条件为土壤饱和持水量(WHC)的40%、60%、90%,通过向温带暗棕壤中添加两种不同性质的氨基酸,探讨其对土壤碳氮含量及CH_(4)排放的潜在影响,运用Pearson相关分析法分析土壤碳氮含量、pH值及CH_(4)排放速率间的相关性。【结果】(1)氨基酸处理显著增加了土壤可溶性有机碳(DOC)含量、铵态氮(NH_(4)^(+)-N)含量及CH_(4)排放速率。亮氨酸处理使DOC、NH_(4)^(+)-N含量分别升高21.39%、45.10%,CH_(4)排放速率较CK升高3.20倍,甲硫氨基酸使DOC、NH_(4)^(+)-N含量分别升高21.39%、72.71%,CH_(4)排放速率较CK升高7.00倍;(2)不同氨基酸对土壤硝态氮(NO_(3)^(-)-N)含量的影响存在差异。亮氨酸处理使土壤NO_(3)^(-)-N含量升高了8.41%,但其对于土壤硝化作用的影响可能存在滞后性,而甲硫氨基酸能够显著抑制土壤硝化作用,NO_(3)^(-)-N含量显著降低了37.90%;(3)土壤不同水分条件对土壤DOC、NH_(4)^(+)-N、NO_(3)^(-)-N含量及CH_(4)排放速率均存在显著影响。90%WHC使DOC含量升高11.95%~19.91%,使NH_(4)^(+)-N升高19.83%~35.46%,使NO_(3)^(-)-N降低10.05%~23.79%,使CH_(4)排放速率升高至另外两种水分条件的1.48~2.06倍。60%WHC条件使NH_(4)^(+)-N升高13.05%,使NO_(3)^(-)-N含量升高24.62%。60%WHC可能是温带暗棕壤硝化作用的最适含水量,90%WHC条件有利于DOC积累,同时对NO_(3)^(-)-N的产生存在明显抑制作用;(4)土壤pH与N H4+-N含量呈极显著正相关,与NO_(3)^(-)-N含量呈正相关。CH_(4)排放速率与NO_(3)^(-)-N含量呈极显著负相关,与NH_(4)^(+)-N含量呈负相关,与DOC含量呈极显著正相关。【结论】不同性质氨基酸添加在温带森林暗棕壤碳氮含量及CH_(4)排放中发挥的作用不尽相同。一定范围内,土壤水分含量的升高有利于土壤NH_(4)^(+)-N、NO_(3)^(-)-N、DOC的积累及CH_(4)的排放,但土壤高含水量条件对NO_(3)^(-)-N的产生具有抑制作用。因此,在研究温带森林暗棕壤碳含量、CH_(4)排放及氮转化机制时,建议关注不同氨基酸的差异性作用,同时考虑水分的变化。

Effects of slow-release urea fertilizers on urease activity, microbial biomass, and nematode communities in an aquic brown soil

A field experiment was carried out at the Shenyang Experimental Station of Ecology (CAS) in order to study the effects of slow-release urea fertilizers high polymer-coated urea (SRU1), SRU1 mixed with dicyandiamide DCD (SRU2), and SRU1 mixed with calcium carbide CaC2 (SRU3) on urease activity, microbial biomass C and N, and nematode communities in an aquic brown soil during the maize growth period. The results demonstrated that the application of slow-release urea fertilizers inhibits soil urease activity and increases the soil NH4+-N content.Soil available N increment could promote its immobilization by microorganisms. Determination of soil microbial biomass N indicated that a combined application of coated urea and nitrification inhibitors increased the soil active N pool. The population of predators/omnivores indicated that treatment with SRU2 could provide enough soil NH4+-N to promote maize growth and increased the food resource for the soil fauna compared with the other treatments.

Spectroscopy-Based Soil Organic Matter Estimation in Brown Forest Soil Areas of the Shandong Peninsula, China

Soil organic matter (SOM) is important for plant growth and production. Conventional analyses of SOM are expensive and time consuming. Hyperspectral remote sensing is an alternative approach for SOM estimation. In this study, the diffuse reflectance spectra of soil samples from Qixia City, the Shandong Peninsula, China, were measured with an ASD FieldSpec 3 portable object spectrometer (Analytical Spectral Devices Inc., Boulder, USA). Raw spectral reflectance data were transformed using four methods: nine points weighted moving average (NWMA), NWMA with first derivative (NWMA + FD), NWMA with standard normal variate (NWMA + SNV), and NWMA with min-max standardization (NWMA + MS). These data were analyzed and correlated with SOM content. The evaluation model was established using support vector machine regression (SVM) with sensitive wavelengths. The results showed that NWMA + FD was the best of the four pretreatment methods. The sensitive wavelengths based on NWMA + FD were 917, 991, 1 007, 1 996, and 2 267 nm. The SVM model established with the above-mentioned five sensitive wavelengths was significant ( R 2 = 0.875, root mean square error (RMSE) = 0.107 g kg −1 for calibration set;R 2 = 0.853, RMSE = 0.097 g kg −1 for validation set). The results indicate that hyperspectral remote sensing can quickly and accurately predict SOM content in the brown forest soil areas of the Shandong Peninsula. This is a novel approach for rapid monitoring and accurate diagnosis of brown forest soil nutrients.

中轻度重金属污染农田土壤的时空特征及改良

为研究农田土壤重金属与速效养分的时空特征以及氮磷增效剂对农田土壤重金属的影响,本试验以受中、轻度污染的酸性棕壤和典型潮土为研究对象,采用田间试验、盆栽试验与室内分析相结合的方法进行研究。结果表明:农田土壤中Cd、Cu、Pb、Zn 4种重金属元素含量在0~20 cm土层显著高于深层土壤;棕壤0~20 cm土层Cd含量超标204%,潮土0~20 cm土层Cd、Zn含量分别超标104%、419%;农田土壤0~20 cm土层重金属有效态含量占比高于深层土壤,棕壤中重金属有效态含量占比高于潮土。棕壤0~20 cm土层全氮、碱解氮、铵态氮、硝态氮、有效磷和速效钾含量均显著高于深层土壤,且随土壤深度增加呈逐渐减小趋势,而潮土中仅全氮、碱解氮和有效磷含量显著高于深层土壤;农田土壤速效养分随时间波动变化,其中硝态氮和铵态氮波动幅度最大,最大变异系数分别为44.1%和47.3%。受污染农田土壤的小麦植株体内Cd、Pb、Cu主要积累在叶片,Zn主要积累在籽粒;不同重金属元素从小麦茎、叶向籽粒的迁移程度差异较大,其中Cd迁移率最小,Zn迁移率最大。氮磷增效剂能显著减少棕壤中重金属有效态含量,底肥+氢醌+双氰胺+生物炭处理的有效态Cd、Cu、Pb、Zn含量较对照(仅加底肥,不加氮磷增效剂)处理分别显著降低24.7%、19.5%、23.7%、18.1%,而在潮土中施用效果不明显。研究表明,农田土壤重金属与土壤养分之间存在一定的相关性,且在土壤垂直分布上大体一致,土壤类型是氮磷增效剂对重金属有效态产生不同影响的重要因素。

Paleoclimate change recorded in the red earth and brown-yellow sediment of Late Quaternary for northeastern part of Guangdong Province,south to the Nanling Mountains,China

The paleoenvironment indicated by the geochronology,major oxides——SiO2,Al2O3 and TOFE(Fe2O3 + FeO),and CIA(Chemical Index of Alteration) value of the red earth and brown-yellow silt primarily characterized by the Linjiang stratigraphic section,based on the geological investigation of Late Quaternary along the river banks of northeastern part of China's Guangdong Province,south to the Nanling Mountains,allow us to hypothesize that the red earth on the first terrace in northeastern part of Guangdong belongs to reticulated red clay developed in a hot-wet environment of the last interglacial period(132―73 ka BP),similar to the monsoon environment in the northern margin of modern tropical zone,while the overlying brown-yellow silt layer mainly accumulated in a monsoon environment of warm temperate zone in the last glacial period(73―11 ka BP),with the aeolian sand LJ3 representing an extreme period of worsening climate.Such a hypothesis corresponds well with predecessors' research on the paleoenvironment indicated by abundant fossils in both south and east to the Nanling Mountains.Hence,it follows that the bioclimatic zone did experience a large and rapid vicissitude in northeastern part of China's Guangdong Province,and even in the full extent of the region south to the Nanling Mountains from the last interglacial period to the last glacial period,with the red earth being replaced by the brown-yellow silty sediment,and even maybe with the Ailuropoda-Stegodon Fauna being replaced by the Penghu Fauna.This study may provide an important geological demonstration for the environmental response to global change in China's low latitudes on a 10 ka scale.

长期施肥对黑土和棕壤团聚体稳定性的影响及驱动因素

【目的】比较长期不同施肥措施对两种典型土壤(黑土和棕壤)团聚体分布和稳定性的影响,探究影响团聚体稳定性的关键因素,为缓解土壤结构退化提供理论支撑。【方法】依托34年黑土和45年棕壤长期定位试验,选取两定位点共有的不施肥(CK)、化肥(NPK)、化肥配施有机肥(NPKM)处理,以及黑土特有的化肥配施秸秆(NPKS)处理、棕壤特有的有机肥——猪厩肥(M)处理,采集0—20 cm土层土壤样品,测定土壤化学性质,采用湿筛法对土壤团聚体进行筛分。【结果】相比于CK,NPK处理下黑土和棕壤大团聚体(>0.25 mm)比例显著降低8.6%和11.3%,团聚体平均重量直径(MWD)分别显著减少18.6%和10.7%,说明单施化肥导致黑土和棕壤团聚体稳定性显著降低;NPKM和M处理下棕壤的MWD分别显著增加44.2%和17.9%,而NPKM处理下黑土MWD未发生显著变化,但NPKS处理下黑土MWD显著提高11.8%,说明在棕壤中施用猪厩肥,黑土中秸秆还田是提高团聚体稳定性的重要措施。土壤团聚体的稳定性主要受土壤化学性质的影响。长期施用化肥(NPK)导致黑土和棕壤的pH和交换性钙、镁离子(Ca^(2+)、Mg^(2+))降低,阻碍了大团聚体的形成和稳定。施用有机物料(M、NPKM、NPKS)抑制了土壤pH的降低,提高土壤颗粒态有机碳(POC)和矿物结合态有机碳(MAOC)的含量,促进有机碳与铁铝氧化物、钙镁离子的结合,推动了黑土和棕壤颗粒的团聚过程,进而维持和提高了团聚体的稳定性。综合分析表明,影响黑土团聚体稳定的因素从大到小依次为络合态氧化铝(Al_(p))、Ca^(2+)、POC、pH、MAOC,其中黑土团聚体稳定性与Al_(p)显著负相关,与其余因素显著正相关。影响棕壤团聚体稳定性的关键因素从大到小依次为POC、络合态氧化铁(Fe_(p))、pH、Mg^(2+)、Ca^(2+)、无定形态氧化铝(Al_(o))、Al_(p)、无定形态氧化铁(Fe_(o)),其中棕壤团聚体稳定性与Al_(o)和Fe_(o)显著负相关,与其他因素显著正相关。【结论】化肥配施有机物料(猪厩肥、秸秆)可以抑制土壤酸化,通过增加土壤POC和Ca^(2+)含量,提高黑土和棕壤团聚体的稳定性,是延缓土壤结构退化的重要施肥措施。

生物炭用量对土壤速效钾含量和烟叶钾吸收的长期效应

为了探明生物炭施用量对土壤和烤烟钾的长期效应,在贵州省毕节市开展了5年的田间定位试验。采用单因素(生物炭用量0、5、15、20、40 t/hm^(2))随机区组设计,结果表明:生物炭施用后的首年对土壤速效钾含量的增加效果最大,2种土壤上增幅分别为664.21%和223.09%,随后趋于稳定,5年平均增幅分别为82.36%和39.80%。当生物炭用量分别为15、20、40 t/hm时,两种土壤上速效钾含量5年平均分别显著提高72.2%和127.3%、251.1%和22.3%、31.9%和47.6%。同时,烟叶钾含量也显著增加,增幅分别为18.2%和18.4%。综合来看,生物炭用量为15 t/hm^(2)对提高土壤速效钾和初烤烟叶钾含量效果最佳。总之,适量施用生物炭能显著提高土壤速效钾含量和增加初烤烟叶钾含量。