Distribution of nutrient elements within water-stable aggregates of two tropical agro-ecological soils under different land uses

This study evaluated carbon and nutrient distributions within water-stable aggregates (WSA) of soils of two contrasting ecosystems under different land uses. Surface soil samples were collected from uncultivated and cultivated land in rainforest and savannah agro-ecological areas and separated by wet-sieving technique into 4.76–2.0, 2.0–1.0, 1.0–0.50, 0.50–0.25 and <0.25 mm aggregate fractions. The results show that irrespective of the agro-ecological area, cultivation significantly (p < 0.05) reduced the macroaggregate fractions (>0.25 mm) to smaller diameters. Distribution of organic carbon (C), total nitrogen (N) and available phosphorus (P) within the WSA showed preferential enrichment of these elements in the large macroaggregate fraction (4.76–2.0 mm) for the uncultivated soils and microaggregate fraction (<0.25 mm) for the cultivated soils. The overall pattern indicates higher accumulation of C, N and P in the WSA of the uncultivated soils over the cultivated soils. Average distribution of total exchangeable bases (TEB), i.e., sum of Ca²⁺, Mg²⁺, K⁺ and Na⁺, within WSA of the uncultivated soils of the rainforest region were 7.35 and 7.39 cmol/kg for 4.76–2.0 and <0.25 mm fractions, respectively. The distributions of TEB for cultivated soils of the rainforest region were 2.76 cmol/kg (4.76–2.0 mm fraction) and 7.73 cmol/kg for <0.25 mm fraction. This showed that cultivation significantly (p < 0.05) led to 62% reduction in these nutrients in the 4.76–2.0 mm fraction and 5% increase in concentrations of these cations in <0.25 mm fraction. For savannah soils, distributions of TEB were 7.44 and 6.77 cmol/kg for 4.76–2.0 and <0.25 mm fractions, respectively, in uncultivated sites, whereas TEB were 2.19 cmol/kg (4.76–2.0 mm) and 6.35 cmol/kg (<0.25 mm) for cultivated savannah. This indicated that cultivation significantly (p < 0.05) led to 71% and 6% reductions in Ca²⁺, Mg²⁺, K⁺ and Na⁺ concentrations within the 4.76–2.0 and <0.25 mm aggregate fractions, respectively. However, there were 18% and 50% increase in these elements in the 2.0–1.0 and 1.0–0.50 mm fractions of the cultivated soils of the savannah region, respectively. The general trend showed that in uncultivated soils, the 4.76–2.0 and <0.25 mm fractions were preferentially enriched with Ca²⁺, Mg²⁺, K⁺ and Na ⁺; whereas, cultivation led to redistribution of these elements into the smaller aggregates. Since smaller aggregates are preferentially removed by erosion, this study underscores the need for sustainable soil management practices that would minimize nutrient loss when forest or fallow lands are converted to cropland.     

Role of soil organic matter in stabilization of water-stable aggregates in Soils under different types of land use

Three Andosols (used as grassland, upland field, and paddy field) and two Gray Lowland soils (used as upland field and paddy field) were examined to study the role of organic matter in the stabilization of soil aggregates. It was found that prolonged use of Andosols as grassland or as upland field enabled to maintain a higher level of soil organic carbon than use as paddy field. However, paddy soil exhibited a greater aggregate stability (determined by wet-sieving procedure) than soil under upland field or grassland management. Comparison between two Gray Lowland soils also showed that aggregates in the paddy soil were more stable than in the upland field soil. Among organic constituents examined (such as sodium pyrophosphate (SPP)-extractable organic matter and carbohydrates), only the contents of hot water (HW)-extractable carbohydrates of the soils were significantly correlated with aggregate stability. Paddy soils which showed a greater aggregate stability contained a larger amount of HW -extractable carbohydrates in the soils, and a larger amount of HW -extractable carbohydrates regardless of the size of their aggregates compared with other soils. These findings suggest that HW -extractable carbohydrates which represents easily decomposable organic materials may be of special importance for the stabilization of aggregates in the soils.     

Organic matter in density fractions of water-stable aggregates in silty soils: Effect of land use

The location of soil organic matter (SOM) within the soil matrix is considered a major factor determining its turnover, but quantitative information about the effects of land cover and land use on the distribution of SOM at the soil aggregate level is rare. We analyzed the effect of land cover/land use (spruce forest, grassland, wheat and maize) on the distribution of free particulate organic matter (POM) with a density <1.6 g cm⁻³ (free POM_<1.6), occluded particulate organic matter with densities <1.6 g cm⁻³ (occluded POM_<1.6) and 1.6-2.0 g cm⁻³ (occluded POM_1.6-2.0) and mineral-associated SOM (>2.0 g cm⁻³) in size classes of slaking-resistant aggregates (53-250, 250-1000, 1000-2000, >2000 μm) and in the sieve fraction <53 μm from silty soils by applying a combined aggregate size and density fractionation procedure. We also determined the turnover time of soil organic carbon (SOC) fractions at the aggregate level in the soil of the maize site using the ¹³C/¹²C isotope ratio. SOM contents were higher in the grassland soil aggregates than in those of the arable soils mainly because of greater contents of mineral-associated SOM. The contribution of occluded POM to total SOC in the A horizon aggregates was greater in the spruce soil (23-44%) than in the grassland (11%) and arable soils (19%). The mass and carbon content of both the free and occluded POM fractions were greater in the forest soil than in the grassland and arable soils. In all soils, the C/N ratios of soil fractions within each aggregate size class decreased in the following order: free POM_<1.6>occluded POM_<1.6-2.0>mineral-associated SOM. The mean age of SOC associated with the <53 μm mineral fraction of water-stable aggregates in the Ap horizon of the maize site varied between 63 and 69 yr in aggregates >250 μm, 76 yr in the 53-250 μm aggregate class, and 102 yr in the sieve fraction <53 μm. The mean age of SOC in the occluded POM increased with decreasing aggregate size from 20 to 30 yr in aggregates >1000 μm to 66 yr in aggregates <53 μm. Free POM had the most rapid rates of C-turnover, with residence times ranging from 10 yr in the fraction >2000 μm to 42 yr in the fraction 53-250 μm. Results indicated that SOM in slaking-resistant aggregates was not a homogeneous pool, but consisted of size/density fractions exhibiting different composition and stability. The properties of these fractions were influenced by the aggregate size. Land cover/land use were important factors controlling the amount and composition of SOM fractions at the aggregate level.     

Organic matter and water-stable aggregates in soils

The water-stability of aggregates in many soils is shown to depend on organic materials. The organic binding agents have been classified into (a) transient, mainly polysaccharides, (b), temporary, roots and fungal hyphae, and (c) persistent, resistant aromatic components associated with polyvalent metal cations, and strongly sorbed polymers. The effectiveness of various binding agents at different stages in the structural organization of aggregates is described and forms the basis of a model which illustrates the architecture of an aggregate. Roots and hyphae stabilize macro-aggregates, defined as > 250 μm diameter; consequently, macroaggregation is controlled by soil management (i.e. crop rotations), as management influences the growth of plant roots, and the oxidation of organic carbon. The water-stability of micro-aggregates depends on the persistent organic binding agents and appears to be a characteristic of the soil, independent of management.     

Bacterial diversity in water-stable aggregates of soils under conventional and zero tillage management

Reduced tillage of agricultural soils has been shown to result in greater macroaggregation, microbial biomass and microbial diversity. While it has been shown that macroaggregates contain more microbial biomass per unit soil mass than microaggregates, it is unclear how microbial diversity varies with soil aggregation. We investigated the functional diversity (catabolic potential) of bacteria, evaluated by calculating Shannon’s diversity index (H′), substrate richness (S) and substrate evenness (E) from potential substrate utilization patterns, in whole soil (i.e. not separated into different aggregate sizes) and aggregates of different sizes (2–4, 1–2, 0.5–1, 0.25–0.5, and 0.1–0.25 mm diameter) in loam and silt loam soils grown to barley and managed for 6 years under conventional tillage (CT) or zero tillage (ZT) systems in northern British Columbia. There were no significant tillage effects on bacterial diversity in whole soils. In soil aggregates, H′ and E were significantly higher under CT than under ZT on the loam at barley planting time, with no significant aggregate size effects. However, at barley-heading stage, all diversity indices in both soils were significantly higher under ZT than under CT, and they tended to increase with increasing aggregate size. Cluster analysis and principal component analysis of substrate utilization patterns also revealed differences in bacterial community structures between CT and ZT, but the substrates that were utilized differently between the two tillage systems were not the same between soil types or sampling times. The results during the cropping cycle imply that deterioration of soil structure is probably one factor that explains the adverse effects of soil tillage on soil microbial biomass and diversity.     

黑土轻组分C与团聚体水稳性的关系

To evaluate the role of kaolinite and variable charge soils on the hydrolytic reaction of Al, the hydrolysis of Al ions in suspensions of a kaolinite and an Oxisol influenced by organic anions was investigated using changes of pH, Al adsorption, and desorption of pre-adsorbed Al. Kaolinite and the Oxisol promoted the hydrolytic reaction of Al above a certain initial Al concentration （0.1 mmol L^-1 for kaolinite and 0.3 mmol L^-1 for the Oxisol）. The Al hydrolysis accelerated by kaolinite and the Oxisol increased with an increase in initial concentration of Al and was observed in the range of pH from 3.7 to 4.7 for kaolinite and 3.9 to 4.9 for the Oxisol. The acceleration of Al hydrolysis also increased with the increase of solution pH, reached a maximum value at pH 4.5, and then decreased sharply. Al hydrolysis was promoted mainly through selective adsorption for hydroxy-Al. Soil free iron oxides compensated a portion of the soil negative charge or masked some soil surface negative sites leading to a decrease in Al adsorption, which retarded acceleration to some extent. For the Oxisol organic anions increased the proportion of adsorbed Al^3＋ in total adsorbed Al with the increase in soil negative surface charge and eliminated or reduced the acceleration of Al hydrolysis. Different organic anions inhibited the hydrolysis of Al in the order： citrate 〉 oxalate 〉 acetate （under initial pH of 4.5）. The formation of Al-organic complexes in solution also inhibited the hydrolysis of Al.     

Physical properties of peat soils under different land use options

Pristine peat soils are characterized by large porosity, low density and large water and organic matter contents. Drainage and management practices change peat properties by oxidation, compaction and mineral matter additions. This study examined differences in physical properties (hydraulic conductivity, water retention curve, bulk density, porosity, von Post degree of decomposition) in soil profiles of two peatland forests, a cultivated peatland, a peat extraction area and two pristine mires originally within the same peatland area. Soil hydraulic conductivity of the drained sites (median hydraulic conductivities: 3.3 × 10^?5 m/s, 2.9 × 10^?8 m/s and 8.5 × 10^?8 m/s for the forests, the cultivated site and the peat extraction area, respectively) was predicted better by land use option than by soil physical parameters. Detailed physical measurements were accompanied by monitoring of the water levels between drains. The model ‘DRAINMOD’ was used to assess the hydrology and the rapid fluctuations seen in groundwater depths. Hydraulic conductivity values needed to match the simulation of observed depth to groundwater data were an order of magnitude greater than those determined in field measurements, suggesting that macropore flow was an important pathway at the study sites. The rapid response of depth to groundwater during rainfall events indicated a small effective porosity and this was supported by the small measured values of drainable porosity. This study highlighted the potential role of land use and macropore flow in controlling water table fluctuation and related processes in peat soils.     

黑土开垦后水稳性团聚体与土壤养分的关系

Water-stable aggregates, which are an index for the evaluation of the structural properties of the soil, are affected by many factors. Zhaoguang Farm, Longzhen Farm, and Jiusan Farm were chosen as the representative study sites in the region of black soils, a typical soil resource in Northeast China. The variation in the content of 〉 0.25 mm water-stable aggregates and its relationship with the nutrients in black soil were investigated after different years of reclamation. The results showed that the 〉 0.25 mm water-stable aggregates were more in the surface than in the subsurface soil and they changed in the following order： Longzhen Farm 〉 Zhaoguang Farm 〉 Jiusan Farm. The water-stable aggregates decreased sharply at the initial stage of reclamation and then became stable gradually with time. They were significantly correlated with the contents of organic C, total N, total P, and CEC in black soil, with the correlation coefficients r being 0.76, 0.68, 0.61, and 0.81 （P 〈 0.01）, respectively; however, their relationships with available P, available K, and total K were unclear. These showed that organic matter was the cementation of soil water-stable aggregates. Increasing decompositions and decreasing inputs of organic matter after reclamation were responsible for the amount of reduction of the water-stable aggregates. Thus, to maintain good soil aggregate structure, attention should be paid to improvement of soil nutrient status, especially the supply of organic C and N.     

PAM对黄土高原主要土壤类型水稳性团聚体的改良效果及机理研究

通过室内土柱培养,研究PAM对黑垆土、黄绵土、风沙土水稳性团聚体的改良效果,并探讨其作用机理和合理的施用浓度.结果表明,在浓度为0.05%～0.4%,PAM均可促进3种土壤＞0.25 mm水稳性团聚体的形成,并有效降低3种土壤团聚体分形维数,改善土壤结构;方差分析表明,PAM改良3种土壤结构的机理是一致的,将＜1mm的水稳性团聚体聚合为更大粒径的水稳性团聚体,使＞1mm的水稳性团聚体含量增加.PAM改良黑垆土、黄绵土和风沙土土壤水稳性团聚体达到显著水平时的浓度也不相同,其适宜浓度分别为0.2%～0.4%,0.05%,0.05%.3种土壤的黏粒含量和有机质含量的差异,可能是影响PAM对不同土壤的水稳性团聚体的改良效果差异的主要原因.     

Carbon budget in arable gray forest soils under different land use conditions

The effect of different land-use practices on the carbon budget in old arable gray forest soils of Russia was studied in field experiments. A short-term (for 6–7 years) cessation of mineral fertilization had no negative effects on the carbon budget in the agrocenoses studied. Only the combination of zero fertilization with the return to monoculture and the introduction of black fallows created a negative budget of humus in the soil. The regrassing of the eroded arable soil for 24 years increased the humus reserve in the 0- to 60-cm layer by a factor of 1.6–1.7. The average annual accumulation of carbon and nitrogen after the restoration of the perennial vegetation was 106–128 g C/m² and 11–16 g N/m², respectively.     

不同栽培方式菜田耕层土壤重金属状况

【目的】评价不同栽培方式(温室、大棚和露地)菜田土壤重金属状况,为菜田土壤质量改善和蔬菜高效安全施肥提供一定的理论依据。【方法】针对我国北方3个区域(东北、黄淮海、西北地区)和南方4个区域(华中、西南、华东、华南地区)主要蔬菜种植区不同栽培方式的典型菜田耕层土壤展开调查,选择的主要菜区不同栽培方式的菜田均为远离城郊的未受到工业“三废”、汽车尾气等污染的农村菜田,取样时间是2013年作物收获后或蔬菜施肥前或生长后期,共采集503个土壤样品,对温室、大棚和露地三种栽培方式下土壤重金属状况进行了研究。【结果】1)采样区设施(温室和大棚)菜田土壤重金属Cu、Zn和Cd总量总体上均高于露地菜田土壤,较露地菜田土壤平均分别高12.2%、21.7%和30.4%。2)随着种菜年限的增加,菜田土壤重金属Cu、Zn和Cd总量呈显著增加的趋势。不同栽培方式菜田土壤中均可能存在几种重金属同时污染的复合污染现象,土壤Cu、Zn、Cd等之间的相关性均达到极显著水平。3)采样区不同栽培方式菜田土壤Cd的二级超标率在19.2%~22.3%之间,温室、大棚和露地菜田土壤Cd的单项污染指数平均分别为0.97、0.98和0.70;土壤Cu、Zn、Pb、Cr、As和Hg的二级超标率在0~14.6%之间,单项污染指数在0.06~0.52之间。【结论】设施菜田N、P2O5和K2O总量及有机肥用量均显著高于露地菜田,可能是造成设施菜田土壤中重金属Cu、Zn和Cd积累显著高于露地菜田的重要原因。采样区设施(温室和大棚)菜田土壤Cd总体上处于污染警戒级状态,露地菜田土壤总体上未受到Cd的污染;设施和露地菜田土壤Cu、Zn、Pb、Cr、As和Hg总体上均未构成对土壤的污染。     

Kinetics of phosphorus release from calcareous soils under different land use in Iran

The rate of phosporus (P) release from soils can significantly influence P fertility of soils. The objectives of this study were to investigate the effects of land‐use types on the kinetics of P release under different management practices and the relationship between kinetic parameters and soil physical and chemical properties from calcareous soils. The kinetics of P release in 0.01 M CaCl₂ was studied in surface samples of 30 calcareous soils planted to garlic, garden, pasture, potato, vegetables, and wheat. Trend in P‐release kinetics was similar between land‐use types. Significantly different quantities of P were released under different land use. The maximum amount (average of five soils) (46.4 mg kg^–1) of P was released in soil under potato and the minimum amount (10.4 mg kg^–1) under pasture. The kinetics of P release from soils can be described as an initial rapid rate followed by a slower rate. Different models were used to describe P release. In general, parabolic diffusion and power equation were found to be appropriate for modeling P release. The P‐release rate for the soils was estimated by parabolic equation for the studied land‐use types. The constant b was lower for pasture and wheat than for garlic and potato. The relationship between the rate of P release with Olsen‐P was linear, while it was curved with respect to the CaCl₂‐P, indicating that release of P was diffusion‐controlled. When the kinetic parameters of models were regressed on soil properties, CaCl₂‐P and CaCO₃ appeared to be the most important soil properties influencing P‐release rates in these soils.     

长期不同施肥下塿土有机碳和全氮在团聚体中的分布

【目的】研究小麦/玉米轮作体系不同施肥方式下土壤有机碳(SOC)和全氮(TN)在(?)土不同水稳性团聚体中的分布特征,以期深入理解不同施肥方式对土壤碳、氮固持的机制。【方法】采集(?)土21年长期肥料定位试验不同施肥处理0-10 cm和10-20 cm土层土样,分析其水稳性团聚体(2 mm、2~1 mm、1~0.5 mm、0.5~0.25 mm以及0.25 mm)有机碳和全氮的分布特征。试验设不施肥(CK),化肥氮磷钾配施(N、NP、NK、PK、NPK)和秸秆还田配施氮磷钾(SNPK)以及两个水平有机肥与氮磷钾配施(M1NPK、M2NPK)9个处理。【结果】长期施肥0-10 cm土层土壤团聚体SOC和TN含量明显高于10-20 cm,平均增幅20%以上。2~1 mm或1~0.5mm团聚体中SOC和TN的含量最高,0.25 mm团聚体最低。长期不施磷肥处理的土壤团聚体SOC和TN含量均与CK相似。NP、NPK以及SNPK处理,0-10 cm土层SOC较CK分别增加16%~43%、9%~40%和22%~47%;TN增幅分别为28%~48%、39%~61%和39%~91%。10 20 cm土层,NP、NPK以及SNPK处理2mm、2~1 mm、1~0.5 mm土壤团聚体SOC较CK增幅分别为35%~49%、17%~40%和45%~46%,TN增幅分别为44%~47%、39%~54%和54%~64%。长期有机肥与氮磷钾配施处理(M1NPK、M2NPK),0-10 cm土层的团聚体SOC平均较CK分别增加68%~122%和61%~163%,TN平均分别增加84%~133%和97%~175%;10-20 cm土层,SOC较CK平均增幅分别为20%~61%和39%~118%,TN增幅平均分别为43%~86%和107%~136%。SOC和TN主要储存于0.25 mm团聚体中(40%)2~1 mm团聚体储存最少(10%)。长期不施氮或不施磷对SOC和TN在团聚体中的储存比例基本没有影响。长期NP、NPK以及M1NPK、M2NPK均降低了各土层SOC和TN在2 mm或2~1 mm的储存比例增加了在1~0.25 mm团聚体储存比例。2 mm或2~1 mm团聚体的C/N比值高于微团聚体(0.25 mm),而与CK相比,长期施肥降低了土壤团聚体的C/N比值。【结论】关中地区(?)土长期偏施化肥对有机碳和全氮在团聚体的含量及分布没有显著影响而长期氮磷或氮磷钾化肥配合、氮磷钾与有机物配合均明显增加土壤团聚体的有机碳及全氮含量,特别是长期氮磷钾配合有机肥能显著增加土壤1~0.25 mm团聚体对土壤有机碳和全氮的固存比例,提高土壤有机碳和全氮储量减少温室气体的排放。     

Soil organic matter in water-stable aggregates under different soil management practices in a productive vineyard

In a productive vineyard, the influence of different soil management practices on carbon sequestration and its dynamic in water-stable aggregates of Rendzin Leptosol was studied. In 2006, an experiment of different management practices in a productive vineyard was established in the locality of Nitra-Dra?ovce, in the Nitra winegrowing area of Slovakia. The following treatments were established: (1) control (grass without fertilization); (2) T (tillage); (3) T + FM (tillage + farmyard manure); (4) G + NPK3 (grass + NPK 120–55–195 kg ha^?1); and (5) G + NPK1 (grass + NPK 80–35–135 kg ha^?1). The results showed that the lowest soil organic matter content (9.70 g kg^?1) in water-stable microaggregates was determined in G + NPK3, as well as in T. However, the highest soil organic matter content in the highest size fractions of water-stable macroaggregates (>5 mm) was observed in T + FM (19.7 g kg^?1). The highest value for carbon sequestration capacity in water-stable microaggregates was observed in the ploughed farmyard manure treatment. However, the control treatment showed the highest values for carbon sequestration capacity in water-stable macroaggregates, including agronomically favourable size fractions (0.5–3 mm). In all soil management practices under a productive vineyard the most intensive changes in the soil organic matter content were observed in the highest size fractions (>3 mm) of water-stable macroaggregates.     

Texture and sesquioxide effects on water-stable aggregates and organic matter in some tropical soils

Many tropical soils include sesquioxides, which influence the stability of soil organic matter (OM) and aggregation to an extent that is not fully characterized. The present study was carried out on a range of 18 topsoil samples (0–10 cm) from low-activity clay (LAC) soils from sub-Saharan Africa and Brazil, and aimed: (i) at characterizing the size distributions of water-stable aggregates and organic constituents, (ii) at studying how these distributions were affected by texture and sesquioxides, and (iii) how they interacted.The distributions of stable aggregates were generally dominated by macroaggregates (> 200 μm), and those of organic constituents by fine OM (< 20 μm). Aggregation was not clearly affected by soil texture, while total soil carbon (Ct) and the amount of carbon (C) as fine OM increased with soil content in clay plus fine silts (< 20 μm). Stable macroaggregation correlated with Ct and with C amount as fine OM, but each of them correlated more closely with citrate-bicarbonate-dithionite-extractable aluminium (Al), which was not expected. Stable macroaggregation also correlated with C amounts as coarse- and medium-sized OM (> 200 and 20–200 μm, respectively), but each of them correlated more closely with oxalate-extracted Al. These results suggested that for the LAC tropical soils under study OM and aggregate stability depended closely on Al-containing sesquioxides, on Al-substituted crystalline hematite and goethite especially. These sesquioxides also seemed to play a dominant role in the relations between aggregation and OM. As far as soils rich in sesquioxides are concerned, this confirmed that OM is not the main aggregating agent, and suggested that physical protection within aggregates is not necessarily the main mechanism for OM stabilization. However, as soil sesquioxide content cannot be managed easily, the effect of land use on soil OM and aggregation was determinant at the local scale: indeed, for a given location, stable macroaggregation, Ct and C amount as fine OM generally decreased with land use intensification (i.e. cultivation, tillage, reduced surface cover).     

Soil organic matter and water-stable aggregates under different tillage and residue conditions in a tropical dryland agroecosystem

Changes in the proportions of water-stable soil aggregates, organic C, total N and soil microbial biomass C and N, due to tillage reduction (conventional, minimum and zero tillage) and crop residue manipulation (retained or removed) conditions were studied in a tropical rice–barley dryland agroecosystem. The values of soil organic C and total N were the highest (11.1 and 1.33 g kg⁻¹ soil, respectively) in the minimum tillage and residue retained (MT+R) treatment and the lowest (7.8 and 0.87 g kg⁻¹, respectively) in conventional tillage and residue removed (CT−R) treatment. Tillage reduction from conventional to minimum and zero conditions along with residue retention (MT+R,ZT+R) increased the proportion of macroaggregates in soil (21–42% over control). The greatest increase was recorded in MT+R treatment and the smallest increase in conventional tillage and residue retained (CT+R) treatment. The lowest values of organic C and total N (7.0–8.9 and 0.82–0.88 g kg⁻¹ soil, respectively) in macro- and microaggregates were recorded in CT−R treatment. However, the highest values of organic C and total N (8.6–12.6 and 1.22–1.36 g kg⁻¹, respectively) were recorded in MT+R treatment. The per cent increase in the amount of organic C in macroaggregates was greater than in microaggregates. In all treatments, macroaggregates showed wider C/N ratio than in microaggregates. Soil microbial biomass C and N ranged from 235 to 427 and 23.9 to 49.7 mg kg⁻¹ in CT−R and MT+R treatments, respectively. Soil organic C, total N, and microbial biomass C and N were strongly correlated with soil macroaggregates. Residue retention in combination with tillage reduction (MT+R) resulted in the greatest increase in microbial biomass C and N (82–104% over control). These variables showed better correlations with macroaggregates than other soil parameters. Thus, it is suggested that the organic matter addition due to residue retention along with tillage reduction accelerates the formation of macroaggregates through an increase in the microbial biomass content in soil.     

Fertility of tropical soils under different land use systems—a case study of soils in Tabasco,Mexico

Increasing deforestation in Mexico in the past 40 years has led to significant land use changes. It is important to establish land use systems that allow for the necessities of an increasing population and the conservation of soil fertility in the long term. In this study, we investigated the influence of different land use forms on soil fertility in Tabasco, SE Mexico. We chose two different commonly used pastures (Cynodon plectostachyus and Brachiaria decumbens) and a succession forest. We characterised soil fertility by physico-chemical parameters (texture, density, pH, P, Corg., Ntot., cation exchange capacity (CEC)) as well as by biological parameters, such as litter decomposition, microbial biomass and earthworm community. To estimate litter decomposition we used leaves of Gliricidia sepium, a common fodder tree in the region. The three land use systems had very similar soil chemical characteristics. All three can be characterised as acidic (pH between 4.1 and 5.3) with a high content of organic matter and total nitrogen. However, the three land use systems differed significantly with respect to their soil biological characteristics. Earthworm density as well as litter decomposition were significantly lower under B. decumbens than in the other soils. In all land use systems, the participation of macrofauna and mesofauna accelerated litter decomposition rate significantly as compared with decomposition with microfauna and microflora alone.We extracted two components of the pool of data by main component analysis. The acidity component explained mainly the microbial litter decomposition rate. The rate of litter decomposition – with participation of soil meso- and macrofauna – could be explained by the humus component. We assume that biological parameters were more suitable to characterise differences between the different land use systems. The use of C. plectostachyus and succession forest showed a positive effect on soil fertility.     

不同土地利用方式土壤对铜、镉离子的吸附解吸特征

采用一次平衡法对Cu²⁺、Cd²⁺在城市及城郊农田、林地、草地3种土地利用方式土壤中的吸附解吸过程进行比较研究, 结果表明: Cu²⁺、Cd²⁺在3种土地利用方式土壤中的吸附量均随平衡液浓度的增加而增大, Cu²⁺、Cd²⁺在农田土壤上的吸附量均高于林地和草地土壤。分别用Langmuir和Freunlich两种等温吸附方程对吸附过程进行拟合, 3种土壤对Cu²⁺的吸附过程运用Langmuir方程拟合效果好, 而对Cd²⁺的吸附过程运用Freunlich方程拟合效果更好。Cu²⁺在3种土壤的解吸量大小顺序为农田>林地>草地, Cd²⁺在3种土壤的解吸量大小顺序为农田>草地>林地。两种离子在3种土壤中的动态吸附是个快速反应的过程, 随时间延长, 吸附反应趋于平衡。运用双常数函数方程和Elovich方程能较好地拟合重金属在土壤上的吸附动力学过程。Cu²⁺、Cd²⁺的吸附与土壤黏粒含量、有机质含量、CEC和pH均有关。     

Chemical fractionation of phosphorus in calcareous soils of Hamedan,western Iran under different land use

We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl‐P (labile P), NaOH‐P (Fe‐Al‐bound P), HCl‐P (Ca‐bound P), and residual P (Res‐P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca‐bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (< 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe‐Al‐bound P comprised < 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long‐term fertilization increased P allocation to inorganic fractions, as Ca‐bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe‐Al‐bound P (r = 0.534, p < 0.01), labile P and Ca‐bound P (r = 0.574, p < 0.01), Ca‐bound P and Fe‐Al‐bound P (r = 0.504, p < 0.01), Olsen‐P and CaCl₂‐P (r = 0.821, p < 0.01) was found. Principal‐component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.     

不同土地利用方式下紫色土中铵的容量和强度（Q/I）关系

研究了4种土地利用方式下(水田、旱地、林地、菜地)紫色土(紫色湿润雏形土)和紫色水稻土(紫色水耕人为土)NH4+的容量和强度(Q/I)关系。结果表明:紫色土和紫色水稻土NH4+Q/I曲线的曲线部分均出现在NH4+的活度比(ARNH4)较低时,表明土壤存在非交换性NH4+(或专性吸附的NH4+)的释放。紫色土和紫色水稻土NH4+的潜在缓冲容量(PBC)为71.47～203.7 cmol kg-1(mol L-1)-1/2;土壤活性NH4+(-ΔNH40)为0.029 5～0.089 7 cmol kg-1,NH4+的平衡活度比(AR0NH4)为0.187×10-3～1.255×10-3(mol L-1)1/2;土壤专性吸附位点(NH4-sas)为0.010 6～0.118 5 cmol kg-1。相关分析和通径分析表明,土壤小于0.002 mm黏粒含量与NH4+PBC及NH4-sas均呈极显著正相关(p<0.01),小于0.002 mm黏粒对PBC的影响主要是间接作用(间接通径系数为0.585),但对NH4-sas则有强烈的直接作用;有机碳与-ΔNH40和AR0NH4均呈极显著正相关(p<0.01),但是有机碳对-ΔNH40有较大的直接效应(直接通径系数为0.966),而对AR0NH4的影响主要以间接效应为主。土壤-ΔNH40与交换性NH4+数值接近且呈极显著相关(r=0.876 4,n=8,p<0.01),而AR0NH4与交换性NH 4+亦呈极显著相关(r=0.983 7,n=8,p<0.01)。土壤小于0.002 mm黏粒和有机碳的差异是导致不同土地利用方式下紫色土交换性NH4+以及Q/I参数的差异的主要原因,交换性NH4+标志的NH4+有效性指标与由Q/I关系得到的NH4+有效性指标类似。