澳大利亚亚热带地区二代肯宁南洋杉林早期测定土壤C、N所需采集土壤样大小研究

Investigations into forest soils face the problem of the high level of spatial variability that is an inherent property of all forest soils. In order to investigate the effect of changes in residue management practices on soil properties in hoop pine （Araucaria cunninghamii Aiton ex A. Cunn.） plantations of subtropical Australia it was important to understand the intensity of sampling effort required to overcome the spatial variability induced by those changes. Harvest residues were formed into windrows to prevent nitrogen （N） losses through volatilisation and erosion that had previously occurred as a result of pile and burn operations. We selected second rotation （2R） hoop pine sites where the windrows （10-15 m apart） had been formed 1, 2 and 3 years prior to sampling in order to examine the spatial variability in soil carbon （C） and N and in potential mineralisable N （PMN） in the areas beneath and between （inter-） the windrows. We examined the implications of soil variability on the number of samples required to detect differences in means for specific soil properties, at different ages and at specified levels of accuracy. Sample size needed to accurately reflect differences between means was not affected by the position where the samples were taken relative to the windrows but differed according to the parameter to be sampled. The relative soil sampling size required for detecting differences between means of a soil property in the inter-windrow and beneath-windrow positions was highly dependent on the soil property assessed and the acceptable relative sampling error. An alternative strategy for soil sampling should be considered, if the estimated sample size exceeds 50 replications. The possible solution to this problem is collection of composite soil samples allowing a substantial reduction in the number of samples required for chemical analysis without loss in the precision of the mean estimates for a particular soil property.     

章古台沙地松树人工林土壤无机氮、微生物生物量碳及微生物生物量氮

The dynamics of soil inorganic nitrogen （NH4^＋ -N and NO3^- -N） and microbial biomass carbon （Cmic） and nitrogen （Nmic） under 30-year-old fenced Pinus sylvestris L. var. mongolica Litvin （SF）, unfenced P. sylvestris L. var. mongolica Litvin （SUF）, and unfenced Pinus densiflora Siebold et Zucc. （DUF） plantations in the Zhanggutai sandy soil of China were studied during Apr. to Oct. 2004 by the in situ closed-top core incubation method. All mentioned C and N indices in each stand type fluctuated over time. The ranges of inorganic N, Cmic, and Nmic contents in the three stand types were 0.7-2.6, 40.0-128.9, and 5.4-15.2 μg g^-1, respectively. The average contents of soil NH4^＋ -N and Cmic under the three 30-year-old pine plantations were not different. However, soil NO3^ -N and total inorganic N contents decreased in the order of SUF ≥ SF ≥ DUF, the Nmic content was in the order of SF = SUF 〉 DUF, and the Cmic：Nmic ratio was in the order of SUF = DUF 〉 SF. Seasonal variations were observed in soil inorganic N, microbial biomass, and plant growth. These seasonal variations had certain correlations with microbe and plant N use in the soil, and their competition for NH4^＋ -N was mostly regulated by soil N availability. The influence of tree species on inorganic N and Nmic were mainly because of differences in litter quality. Lack of gazing decreased the Cmic：Nmic ratio owing to decreased carbon output and increased the ability of soil to supply N. The soil N supply under the P. sylvestris var. mongolica plantation was lower than under the P. densiflora plantation.     

Soluble organic nitrogen pools in adjacent native and plantation forests of subtropical Australia

Soil soluble organic nitrogen (SON) can play an important role in soil nitrogen (N) cycling in forest ecosystems. This study examined the effect of land-use change from a native forest (NF) to a first rotation (1R) and subsequent second rotation (2R) hoop pine (Araucaria cunninghamii) plantation on soil SON pools. The impact of residue management on SON pools was also investigated in the 2R forest, where SON was measured in tree rows (2R-T) and windrows (2R-W). Various extraction techniques were used to measure SON pool size in the 0-10, 10-20 and 20-30 cm layers of soil. The results showed that land-use change had a significant impact on soil SON pools. In the 0-10 cm layer, 3.2-8.7, 14-23, 20-28, 60-160 and 127-340 mg SON kg⁻¹ were extracted by water, 0.5 M K₂SO₄, 2 M KCl, hot water and hot 2 M KCl, respectively. The size of the SON pools and the potential production of SON (PPSON) were generally highest in the NF soil and lowest in the 2R-T soil, and in all forest types decreased with soil depth. The larger SON pools in the NF soil coincided with lower soil, litter and root C:N ratios, suggesting that the difference in the size of SON pools between the NF and 1R soil may be related to differences in the quality of organic matter input under the different forest ecosystems. Differences in the size of SON pools between the 1R soil and the 2R soils and between the 2R-T soil and the 2R-W soil may be related to the quantity of organic matter input and time since disturbance. Significant relationships were found between the SON extracted by 0.5 M K₂SO₄ (SON_ps) and 2 M KCl (SON_KCl), and also among the SON extracted by hot 2 M KCl (SON_hKCl), hot water (SON_hw) and water (SON_w), suggesting that the organic N released by these groups of extracts may be at least partly from similar pools.     

Soil biological changes for a natural forest and two plantations in subtropical China

Conversion of natural forests into pure plantation forests is a common management practice in subtropical China. To evaluate the effects of forest conversion on soil fertility, microbe numbers and enzyme activities in topsoils (0-10 cm) were quantified in two 33-year-old monoculture plantations of Castanopsis kawakamii Hayata (CK) and Cunninghamia lanceolata Lamb. (Chinese fir) (CF), and compared to a neighboring relict natural C. kawakamii forest (NF), in Sanming, Fujian. Five soil samples were collected once each in January, April, July, September and November in 2000 in each forest for laboratory analysis. Over the sampling year, there were significant differences for bacteria, fungi and actinomycetes between forests and between seasons (P < 0.05). The largest bacteria and fungi populations were in NF, while CF contained the greatest number of actinomycetes. There were also significant differences (P < 0.05) with microbial respiration for forests and seasons. Additionally, compared with NF, urease and acid phosphatase were significantly lower (P < 0.05) in CK and CF. Also, the correlations of soil hydrolysable N and available P to soil microbial and enzymatic activities were highly significant (P < 0.01). Thus, to alter the traditional Chinese fir monoculture so as to mimic the natural forest conditions, managing mixed stands of Chinese fir and broadleaf trees or conducting crop rotation of conifers and broadleaf trees as well as minimizing forest disturbances like clear-cutting, slash burning and soil preparing, could be utilized.     

Effects of nitrogen fertilization on soil nitrogen pools and microbial properties in a hoop pine (Araucaria cunninghamii) plantation in southeast Queensland, Australia

A field study was conducted to investigate the effects of N fertilization on soil N pools and associated microbial properties in a 13-year-old hoop pine (Araucaria cunninghamii) plantation of southeast Queensland, Australia. The treatments included: (1) control (without N application); (2) 300 kg N ha^-1 applied as NH₄NO₃; and (3) 600 kg N ha^-1 as NH₄NO₃. The experiment employed a randomized complete block design with four replicates. Soil samples were taken approximately 5 years after the N application. The results showed that application of 600 kg N ha^-1 significantly increased concentrations of NH₄⁺-N in 0-10 cm soil compared with the control and application of 300 kg N ha^-1. Concentrations of NO₃^--N in soil (both 0-10 cm and 10-20 cm) with an application rate of 600 kg N ha^-1 were significantly higher compared with the control. Application of 600 kg N ha^-1 significantly increased gross N mineralization and immobilization rates (0-10 cm soil) determined by ¹⁵N isotope dilution techniques under anaerobic incubation, compared with the control. However, N application did not significantly affect the concentrations of soil total C and total N. N application appeared to decrease microbial biomass C and N and respiration, and to increase the metabolic quotient (qCO₂) in 0-10 cm soil, but these effects were not statistically significant. The lack of statistical significance in these microbial properties between the treatments might have been associated with large spatial variability between the replicate plots at this experimental site. Spatial variability in soil microbial biomass C and N was found to relate to soil moisture, total C and total N.     

Effects of microbial inoculations on soil chemical,biochemical and microbial biomass carbon of cassava (Manihot esculenta Crantz) growing Vertisols

Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P₂O₅:K₂O (NPK) rate (50:25:50 kg ha^?1) significantly increased soil available nitrogen (142.81 kg ha^?1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha^?1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g^?1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g^?1 soil h^?1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g^?1 soil) and β-glucosidase activity (48.82 μg PNP g^?1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g^?1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.     

Effect of Overlying Windrowed Harvest Residues on Soil Carbon and Nitrogen in Hoop Pine Plantations of Subtropical Australia (6 pp)

Background, Aim and Scope   Harvest residues were formed into windrows to prevent nitrogen (N) losses through volatilisation and erosion that occurred following pile and burn operations in hoop pine (Araucaria cunninghamii Aiton ex A. Cunn.) plantations of subtropical Australia. We selected second rotation (2R) hoop pine sites where the windrows (10-15 m apart) had been formed 1, 2 and 3 years prior to sampling in order to examine soil carbon (C) and N in the areas beneath and between the windrows. Materials and Methods: We used conventional chemical methods, anaerobic incubation assay, 13C and 15N natural abundance analyses and, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Results: Percent mineralisable N (PCMN) was the only parameter in the underneath windrow position at the Year 1 site that did not show a significant difference to the rest of the positions along the transect. However, positions adjacent to windrows did have significantly greater PCMN at the Year 1 site than other positions along the transect. PCMN, total N and total C were significantly greater underneath the windrows at the Year 3 site, whilst d13C was significantly more negative in the underneath windrow positions. Discussion: PCMN was the most sensitive biological indicator of the changes occurring in the soil due to decomposition of the windrows, with the beneath-windrow position having a significantly higher PCMN than the inter-windrow position (p<0.001) at the Year 3 site. Isotopic natural abundance for both 13C and 15N was able to detect the influx of labile materials from new residues. Solid-state 13C NMR was able to detect inputs of labile C from the windrows at the Year 1 site, whilst the increase in aromatic C at the Year 3 site was indicative of the more advanced stages of windrow decomposition. Conclusions: Decomposition of windrowed residues had a beneficial effect on soil N and C pools. However, the effect remained localised after 3 years, indicating that trees needed to be planted close to the windrows to gain any benefit from residue decomposition Recommendations and Perspectives: The use of windrows allows a clear planting area and provides a good barrier against soil erosion. However, trees can only gain access to the nutrients from the decomposing residues if they are planted close to the windrows. Limiting the width of the cleared areas to allow for only 2 planting rows will give the maximum benefit to the developing trees.     

Physical,chemical and microbiological soil attributes influence soil greenhouse gases fluxes in Atlantic Forest and pine (Pinus taeda) plantations in Brazil

Forest soils can be sources or sinks of greenhouse gases (GHGs) depending on soil attributes that affect biomass and activity of soil micro-organisms involved in GHGs fluxes. In this work, we tested the hypothesis that soil physical, chemical and microbiological attributes, under different forests ecosystems, affect the soil GHGs [nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄)] fluxes. The study was carried out in two locations in southern Brazil in 2019, with three experimental plots of 900 m² in native forests of the Atlantic Forest biome and in loblolly pine (Pinus taeda) plantations. Air samples released from the soil surface were analysed for concentration and flux of CO₂, N₂O and CH₄. Soil samples were analysed for chemical attributes, density (Ds), soil microporosity (MiPs), soil macroporosity (MaPs), total porosity (TP), water-filled pore space (WFPS), microbial biomass carbon (MB-C), basal respiration (BR), microbial (qMic) and metabolic (qCO₂) quotient and activities of soil urease and β-glucosidase enzymes. The seasons influenced the CO₂ and N₂O emissions, probably because of the changes in seasonal conditions. However, native forests consumed more CH₄ than pine plantations. Meanwhile, the native forests presented soils with lower Ds (average 21.5% lower), more TP (average 12.5% higher) and more moisture (average 33% higher), which improved the microbiological attributes of the soil (20% to 60% more MB-C, 67% higher urease activity and 30% higher β-glucosidase activity) compared with pine plantations. Native forests contributed more intensely to CH₄ consumption than pine plantations because they present better physical, chemical and microbiological soil conditions. Therefore, it is possible that forestry practices that improve soil physical attributes are likely to contribute to increase CH₄ consumption, and to reduce GHGs emissions in forest ecosystems.     

Mineralization of carbon and nitrogen,and nitrification in Scots pine forest soil treated with fast- and slow-release nitrogen fertilizers

We studied the effects of fast- and slow-release organic N fertilizers (urea and urea-formaldehyde, Nitroform) on mineralization, nitrification, and N leaching in an acid, poor forest soil. We also studied the effects of a nitrification inhibitor (dicyandiamide) applied together with urea. Net nitrification, mineralization of N and C were determined by aerobic laboratory incubation of soil samples taken one and three growing seasons after N application. Numbers of autotrophic nitrifiers were estimated by a most probable number method three growing seasons after the treatment. Urea increased the CO₂ production immediately after application, but after three growing seasons, CO₂ production was the lowest in the urea-treated soils. In the nitroform-treated soils, the concentration of exchangeable NH _inf4 ^sup+ after the first and third growing seasons was of the same magnitude, in contrast to the urea-treated soils, where hydrolysis took place immediately. Three growing seasons after application, the highest amount of NH _inf4 ^sup+ accumulated during the laboratory incubation was in the nitro-form-treated soils. Unlike urea, nitroform did not increase the production of NO _inf3 ^sup- or the number of NH _inf4 ^sup+ oxidizers. In the urea+dicyandiamide-treated soils there was less NO _inf3 ^sup- and a lower number of nitrifiers than in the urea-treated soils. The results showed that a slow-release N fertilizer, such as nitroform, increases the availability of mineral N in acid forest soils without increasing nitrification and hence the risk of NO _inf3 ^sup- leaching.     

牧场土壤碳、氮和微生物动力学研究:放牧强度和种植方式的影响

Management intensity critically influences the productivity and sustainability of pasture systems through modifying soil microbes, and soil carbon(C) and nutrient dynamics; however, such effects are not well understood yet in the southeastern USA. We examined the effects of grazing intensity and grass planting system on soil C and nitrogen(N) dynamics, and microbial biomass and respiration in a long-term field experiment in Goldsboro, North Carolina, USA. A split-plot experiment was initiated in 2003 on a highly sandy soil under treatments of two grass planting systems(ryegrass rotation with sorghum-sudangrass hybrid and ryegrass seeding into a perennial bermudagrass stand) at low and high grazing densities. After 4 years of continuous treatments, soil total C and N contents across the 0–30 cm soil profile were 24.7% and 17.5% higher at the high than at the low grazing intensity, likely through promoting plant productivity and C allocation belowground as well as fecal and urinary inputs. Grass planting system effects were significant only at the low grazing intensity, with soil C, N, and microbial biomass and respiration in the top 10 cm being higher under the ryegrass/bermudagrass than under the ryegrass/sorghum-sudangrass hybrid planting systems. These results suggest that effective management could mitigate potential adverse effects of high grazing intensities on soil properties and facilitate sustainability of pastureland.     

Nitrogen pools and turnover in arable soils under different durations of organic farming: I: Pool sizes of total soil nitrogen,microbial biomass nitrogen,and potentially mineralizable nitrogen

Soil organic matter contents, soil microbial biomass, potentially mineralizable nitrogen (N) and soil pH values were investigated in the Ap horizons of 14 field plots at 3 sites which had been under organic farming over various periods. The objective was to test how these soil properties change with the duration of organic farming. Site effects were significant for pH values, microbial biomass C and N, and for potentially mineralizable N at 0—10 cm depth. The contents of total organic C, total soil N, and potentially mineralizable N tended to be higher in soils after 41 versus 3 years of organic farming, but the differences were not significant. Microbial biomass C and N contents were higher after 41 years than after 3 years of organic farming at 0—10 cm depth, and the pH values were increased at 10—27 cm depth. Nine years of organic farming were insufficient to affect soil microbial biomass significantly. Increased biomass N contents help improve N storage by soil micro‐organisms in soils under long‐term organic farming.     

江门市新会区耕地土壤有效性Si,Ca,Mg的空间变异特征

运用地统计学,结合GIS技术研究了江门市新会区土壤有效性Si、有效性Ca和有效性Mg3种元素含量的空间分布特征。结果表明,各变量经对数转换后符合正态分布。半方差分析的结果显示,除了有效性Ca具有强空间相关外,其余的都具有中等空间相关性。从Kriging插值结果可知,有效性硅含量在115 2 30mg/kg的面积占研究区域耕地面积的34.9% ,主要分布于研究区域的中部和东北部地区;有效性Ca的含量在>10 0 0mg/kg的面积占研究区域耕地面积的71.6 % ,主要分布在研究区域的东北、中部和西北、南部的部分地区;有效性Mg的含量在>30 0mg/kg的面积占研究区域耕地面积的2 9.8% ,主要分布于研究区域的东北部地区     

添加调节N和P浓度后的植物残体对土壤呼吸作用、微生物量和养分有效性的影响

Microbial activity and nutrient release are known to be influenced by organic matter properties,but it is difficult to separate the effect of C/N ratio from that of C/P ratio because in most plant residues both ratios are either high or low.An incubation experimeut was conducted to investigate the effects of reducing the C/N and C/P ratios of slowly decomposable plant residues (young eucalyptus leaves,mature wheat straw,and sawdust) to those of rapidly decomposable residues (young kikuyu shoots) on soil respiration,microbial biomass,and N and P availability.The C/N and C/P ratios of the former were adjusted to 15 and 89,respectively,by adding N as (NH4)2SO4,P as KH2PO4 or both and residues were added at 10 g C kg-1 to a silt loam.Soil respiration was measured over 21 d;microbial biomass C (MBC) and available N and P were measured on days 0,7,and 21.Compared to the unamended soil,addition of kikuyu increased cumulative respiration 20-fold,MBC concentration 4 to 8-fold,and available P concentration up to 4-fold,whereas the increase in available N concentration was small and transient.Cumulative respiration and MBC concentration were low in the sawdust-amended soil and were not influenced by reducing the C/N and C/P ratios.Cumulative respiration with original wheat and eucalyptus was 30％-40％ of that with kikuyu.Reducing the C/N ratio alone or both C/N and C/P ratios increased cumulative respiration and MBC concentration 2-fold compared to the original wheat and eucalyptus,whereas reducing the C/P ratio had little effect.Throughout the experiment,the available N concentration after addition of residues with reduced C/N ratio increased in the following order of eucalyptus ＜ wheat ＜ sawdust.By independently lowering the C/N and C/P ratios,microbial activity was more limited by C and N than P.However,lowering the C/N ratio of very slowly decomposable sawdust had no effect on soil respiration and MBC concentration,suggesting that other properties such as concentration of poorly decomposable C compounds limited decomposition.     

Soil microbial attributes along a chronosequence of Scots pine (Pinus sylvestris var. mongolica) plantations in northern China

Soil microorganisms play a key role in soil organic matter dynamics, nutrient cycling, and soil fertility maintenance in forest ecosystems, and they are influenced by stand age and soil depth. However, few studies have simultaneously considered these two factors. In this study, we measured soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil basal respiration (SBR) rate, and potential extracellular enzyme activity (EEA) in soil to a depth of 60 cm under 10-, 30-, and 40-year-old Scots pine (Pinus sylvestris var. mongolica) stands (Y10, Y30, and Y40, respectively) in plantations in northern China in 2011. Soil water content (SWC), soil pH, soil organic carbon (SOC), and soil total nitrogen (STN) were also measured to explore their effects on soil microbial indices across different stand ages and soil depths. Our results showed that SMBC, SMBN, and the SBR rate were generally higher for the Y30 stand than for the Y10 and Y40 stands. Potential EEA, except forα-glucosidase, decreased significantly with increasing stand age. Soil organic carbon,STN, SWC, and soil pH explained 67%of the variation in soil microbial attributes among the three stand ages. For the same stand age, soil microbial biomass and the SBR rate decreased with soil depth. Lower microbial biomass, lower SBR rate, and lower EEA for the mature Y40 stand indicate lower substrate availability for soil microorganisms, lower soil quality, and lower microbial adaptability to the environment. Our results suggest that changes in soil quality with stand age should be considered when determining the optimum rotation length of plantations and the best management practices for afforestation programs.     

喀斯特山地植烟土壤养分空间变异及分区研究

为揭示喀斯特山地植烟土壤养分空间变异特征并进行分区管理,利用地统计学和模糊C-均值聚类算法对贵州省黔南州喀斯特山地植烟土壤养分进行分析。结果表明,土壤总体呈弱酸性,极小部分土壤缺乏有机质、碱解氮、有效磷、有效铜和有效锌,小部分土壤缺乏速效钾、交换性钙和交换性镁,大部分土壤缺乏有效钼。p H、有机质、碱解氮、有效磷、速效钾、交换性镁、有效铜、有效锌和有效钼空间相关性中等,交换性钙空间相关性弱。p H、有机质、碱解氮、有效磷、速效钾、交换性钙、交换性镁和有效锌空间变异主要由随机因素引起,有效铜和有效钼的空间变异主要由结构性因素引起。土壤养分空间变异趋势效应明显,p H、有效磷、速效钾、交换性钙、交换性镁、有效铜、有效锌和有效钼均由几个高值中心向四周递减分布;有机质和碱解氮均由北部、西部和南部向中部和东部递增分布。研究区植烟土壤可分为4个管理分区,分区内土壤养分趋于同质化,分区间差异显著。本研究为喀斯特山地农田土壤养分管理、农作物平衡施肥和肥料高效利用提供了参考依据。     

The effects of N and P additions on soil microbial properties in paired stands of temperate secondary forests and adjacent larch plantations in Northeast China

The conversion of secondary forests to larch plantations in Northeast China has resulted in a significant decline in soil available nitrogen (N) and phosphorus (P), and thus affects plant productivity and ecosystem functioning. Microbes play a key role in the recycling of soil nutrients; in turn, the availability of soil N and P can constrain microbial activity. However, there is little information on the relationships between available soil N and P and the microbial biomass and activity in larch plantation soil. We studied the responses of soil microbial respiration, microbial biomass and activity to N and P additions in a 120-day laboratory incubation experiment and assessed soil microbial properties in larch plantation soil by comparing them with the soil of an adjacent secondary forest. We found that the N-containing treatments (N and N + P) increased the concentrations of soil microbial biomass N and soluble organic N, whereas the same treatments did not affect microbial respiration and the activities of β-glucosidase, N-acetyl-β-glucosaminidase and acid phosphatase in the larch plantation. In addition, the concentration of microbial biomass P decreased with N addition in larch plantation soil. In contrast, N and N + P additions decreased microbial respiration, and N addition also decreased the activity of N-acetyl-β-glucosaminidase in the secondary forest soil. The P treatment did not affect microbial respiration in either larch plantation or secondary forest soils, while this treatment increased the activities of β-glucosidase and acid phosphatase in the secondary forest soil. These results suggested that microbial respiration was not limited by available P in either secondary forest or larch plantation soils, but microbial activity may have a greater P demand in secondary forest soil than in larch plantation soil. Overall, there was no evidence, at least in the present experiment, supporting the possibility that microbes suffered from N or P deficiency in larch plantation soil.     

Changes in soil properties related to conversion of savannah woodland into pine and eucalyptus plantations,Northern Nigeria

Soil properties associated with six age-grade plantations of Pinus oocarpa Schiede and Eucalyptus camaldulensis Dehnh., respectively, including nearby natural vegetation, were compared in the savannah zone of Nigeria. The soil organic matter, total nitrogen and exchangeable nutrients first show declining values with the increasing age of the plantation, then an increase and finally steady or declining values in the 0–15 cm soil depth. Usually the differences between the two youngest plantations and the oldest plantations, and the natural vegetation, were significant. In the 20–30 cm soil depth the properties showed a decrease or steady values over time, with the three oldest plantations showing significant differences from the natural vegetation. The soil pH showed an increased acidity over time. There was little difference in the soil properties between the two tree species. The implications of the results are discussed in relation to sustaining productivity and soil fertility. © 1998 John Wiley & Sons, Ltd.     

养分与田间管理对杂交稻种植体系中土壤微生物群落底物利用模式的联合效应

A field experiment was conducted to study the combined effect of nutrient and pest managements on soil biomass phospholipid contents,functional biodiversity and substrate utilization patterns of soil microbial populations in hybrid rice cropping system. The mineral N,P and K fertilizers (as urea,calcium superphosphate and KCl respectively) were incorporated at 100,25,and 100 kg ha^-1,respectively, and the various pesticides were applied at the recommented rates. The results of the experiment demonstrated a decline in the microbial abundance and soil microbial biomass phospholipid contents with the advancement of crop growth, and significant changes in substrate utilization pattern of soil microbial population studied were observed with different management practices and at different growth stages. The principal component analysis (PCA) using all 95-carbon sources (BIOLOG plates) gave good differentiation among the treatments, indicating that they have different patterns of carbon utilization under different habitats. The data showed that diversity in microbial community continuously changed with the progression in crop stage,particularly at physiological maturity (PM) stage that was evident from the utilization of different carbon sources at various crop stages.     

Changes in soil organic carbon and nutrient pools in aggregate-sized fractions along a chronosequence of wolfberry (Lycium barbarum L.) plantations in arid areas of Northwest China

Different land use and management actions can affect soil aggregates (SAs) and nutrient stocks, which are crucial for sustainable agriculture. The impacts of various chrono-sequences on the soil aggregate structure, soil organic carbon (SOC) and nutrients associated with aggregate fractions in wolfberry (Lycium barbarum L.) plantations are still not fully understood. This study examined the composition and stability of SAs, SOC, total nitrogen (TN), available phosphorus (AP) and exchangeable cations (K⁺, Na⁺, Ca²⁺ and Mg²⁺) in bulk soil and various aggregate-size fractions from five wolfberry plantations with varying ages (1, 4, 6, 10 and 13 years) and a corn field (0 years) in the arid region of northwest Ningxia in China. The results indicated that silt–clay (<53 μm) fractions were dominant in the soil, accounting for 51%–66%, under different plantation ages. The proportion of the macro-aggregates (>250 μm) increased significantly, by 40%–47%, over the 4 years of wolfberry plantation. Likewise, the soil aggregate stability was improved, and total exchangeable bases (TEB) along with numerous cations concentrations (K⁺, Na⁺, Ca²⁺ and Mg²⁺) in SAs were significantly reduced as the wolfberry plantings became older. Both concentrations of SOC and TN in the soil aggregates peaked in the 13th year. The silt–clay fractions stored a considerable amount of SOC and nutrients. However, short-term (under 6 years) cultivation of wolfberry reduced the stocks of SOC, TN and AP in the soil, while long-term (over 10 years) cultivation increased them, particularly in macro-aggregates. These findings indicated that long-term wolfberry farming had several advantages, such as enhancing soil structure, accumulating SOC and nutrients and ameliorating alkaline soils, especially after 10 years, in the arid northwest of China.