Distribution Of Water-stable Aggregates Research Articles

Exogenous easily extractable glomalin-related soil protein promotes soil aggregation, relevant soil enzyme activities and plant growth in trifoliate orange

Studies on glomalin-related soil protein (GRSP) have focused on soil aggregation and fungal physiology, whereas it is not known how exogenous GRSP could positively impact on these processes, soil enzyme activity and plant growth. Easily extractable GRSP [EE-GRSP, 0.022 mg protein/mL citrate buffer (20 mmol, pH 7.0)] from a 26-year-old citrus orchard was exogenously applied into 5-month-old potted trifoliate orange ( Poncirus trifoliata ) for 3 months to evaluate effects on soil water-stable aggregate distribution, relevant soil enzyme activities and plant growth. Depending on the applied concentrations as 1/2, 1/4 or full strength, exogenous EE-GRSP generally significantly increased the distribution of soil water-stable aggregates and mean weight diameter (MWD, an aggregate stability indicator). Values of MWD and plant biomass production curvilinearly positively correlated with exogenous EE-GRSP applications. Exogenous EE-GRSP generally significantly increased the activity of rhizospheric polyphenol oxidase, peroxidase, acid and alkaline phosphatase. Both the 1/2-strength and 1/4-strength, but not the full-strength exogenous EE-GRSP, significantly stimulated plant growth performance. Our results firstly demonstrated the positive contribution of exogenous EE-GRSP to soil aggregation, relevant rhizospheric enzyme activities and/or plant growth, which has important implications for exploring GRSP in enhancing soil structure and/or plant performance.

Temporal variations of the distribution of water-stable aggregates, microbial biomass and ergosterol in temperate grassland soils with different cultivation histories

In grassland soils, the temporal dynamics in different fractions of soil organic carbon (SOC) is not completely understood. We investigated the temporal variations of water-stable aggregates, microbial biomass C (Cmic) and ergosterol concentrations (as a proxy for fungal biomass) in loamy sandy soils under grassland (north of Kiel, Germany). Samples were taken six times between October 2010 and October 2011 from i) a permanent grassland, ii) an arable plot converted to grassland and iii) a grassland with a one-time tillage operation (both in September 2010). Water-stable aggregate concentrations were determined by a wet-sieving procedure, Cmic concentrations by chloroform-fumigation-extraction and ergosterol concentrations by ethanol extraction. Temporal variation in aggregate distribution of soil samples from the permanent grassland was considerable: the large macroaggregate (>2000μm) concentrations (mean±standard error, n=3) in the surface soil (0–10cm) were highest in October 2011 (666±12gkg−1) and lowest in May (206±49gkg−1). The tillage operation in grassland led to lower concentrations of large macroaggregates, ergosterol and Cmic in the surface soil than in the permanent grassland. The conversion of arable land into grassland did not affect macroaggregate concentrations, despite an increase in Cmic (1.4-fold) and ergosterol concentration (3.3-fold) in the surface soil. Multiple linear regression analysis described the variations in the large macroaggregate concentration satisfactorily (R2=0.60) and indicated that the gravimetric moisture content and the Cmic concentration had positive effects and the pH a negative effect. While ergosterol concentrations (mean±standard error) showed some temporal variations (values for the surface soil in the grassland ranged from 0.5±0.1 to 1.5±0.1mgkg−1), Cmic concentrations varied much less, indicating a higher sensitivity of ergosterol to soil cultivation or changing environmental conditions.

Effect of Distillery Effluent (Spent Wash) Application on Aggregate Size Distribution and Stability in Sodic Soils

Sodic soils of sandy loam, silt loam and clay loam textures having exchangeable sodium percentage (ESP) classes of 20, 40, 60 and 80 were reclaimed with 0, 10, 20, 30 and 40 % solutions of distillery effluent (DE) and gypsum in columns. Soil texture, types of amendment and initial ESP had a larger impact on chemical properties, aggregate stability and size distribution. With increase in concentration of DE, a significant reduction in ESP, pH and insignificant increase in electrical conductivity (EC) of soil was observed for all three textures. Organic carbon (OC) content was also increased significantly in soils amended with DE. Size distribution of water-stable aggregates (WSA) of soils reclaimed using 40 % solution of DE and gypsum were found at par. Depending upon initial ESP and type of amendments used, mean weight diameter (MWD) of WSA varied from 0.51 to 1.14, 0.61 to 1.37 and 0.54 to 1.63 mm for sandy loam, silt loam and clay loam soils respectively. The percentage of water-stable macro-aggregates (WSMA) (>2 mm diameter) ranged from 2.2 to 18.2 in sandy loam, from 2.2 to 19.5 in silt loam and from 4.6 to 28.5 in clay loam soils. Combined as well as individual effects of initial ESP, EC, pH, and OC were found highly significant on WSMA and MWD of WSA in distillery effluent amended soils.

Dinâmica de agregação do solo em sistemas orgânicos mono e policultivados com culturas de milho, feijão e abóbora

The ability of plants to corn, beans and squash was studied in monocultures and polycultures with two and three species in macroagregacao regain ground after conventional tillage in organic production systems. The distribution of water-stable aggregates in diameter classes 8-4, 4-2, 2 to 0.25, <0.25 mm, and weighed wet (DMPU) average diameter, in the 0.00-0.10 layer m, were evaluated at three times t1) before conventional tillage; t2) after preparation, and t3) at the end of the crop cycle. Dynamics of aggregation in time showed the negative effect of soil tillage with disruption of macroaggregates in all treatments, decreasing the DMPU 2.44 mm before cooking to 2.14 after this, even without change occurs in carbon , observed the positive effect of the action of plants in the recovery of aggregation during the cycle of 94 days when the DMPU increased to 2.48 mm.

Aggregation and soil organic carbon fractions under different land uses on the tableland of the Loess Plateau of China

Land uses and cultivation are important factors controlling SOC storage on the Loess Plateau. These factors may also affect the relative importance of different mechanisms for the stabilization of organic matter in the soil. Easily oxidizable organic carbon (EOC), aggregation and aggregate C fractions in the soil were measured under different land uses. Aggregates were fractionated using a wet-sieving procedure to obtain the distribution of water-stable aggregates. The fractions of aggregates, aggregate SOC and aggregate EOC in grassland and forestland were generally higher than those in farmland. Furthermore, because conventional cultivation destroyed aggregates, the dominant aggregate size fractions were <0.5mm for farmland and >0.5mm for other land uses. Compared to the corresponding values in farmland, the mean weight diameter (MWD) in forestland and grassland increased by 808%–417%, and the stability ratio of water-stable aggregate (WSAR) increased by 920%–553%. Aggregate formation and its dominant size fraction were associated closely with its carbon fractions. SOC and EOC in farmland tended to be concentrated in smaller-sized aggregates, whereas SOC and EOC under other land uses tended to concentrate in larger-sized aggregates. EOC tended to concentrate in larger aggregates than SOC. The small fractions of the aggregates formed large fractions by combining with fresh organic matter. So converting slope farmland to forestland and grassland could improve the storage and quality of SOC, and the tendency of SOC transfer.

Soil aggregation and distribution of carbon and nitrogen in different fractions after 41 years long-term fertilizer experiment in tropical rice–rice system

Inorganic fertilizers and manure application can alter the aggregate distribution as well as aggregate associated organic carbon and nitrogen. It is not fully understood how long term addition of carbon (C) and nitrogen (N) through biomass, farm yard manure (FYM) and inorganic fertilizers are distributed in soil aggregates in a tropical rice–rice system. Therefore, the objectives of this study were to investigate the long-term effects of FYM and inorganic fertilizer in a rice–rice system on (i) distribution of water stable aggregates in the soil, and (ii) amount of total soil organic carbon (TOC), total N and C/N ratio in different aggregate fractions. The total water stable aggregates (WSA) ranged from 71.6% under control to 91.1% under NPK+FYM in the surface soil (0–15cm). The incorporation of FYM increased the macroaggregates (5–2mm) by 165.3% and mesoaggregates by 130.7% (2–1mm) and 282.8% (1–0.5mm) over control in 0–15cm soil layer. Mean weight diameter (MWD), varied from 0.43 to 0.78 in 0–15cm and from 0.40 to 0.72 in 15–30cm soil layer. MWD was higher under FYM treated plots than inorganic fertilizer alone and unfertilized control plots. Irrespective of treatment, macroaggregates (5–2mm) had the highest (4.13–14.03gkg−1) and microaggregate fraction (0.25–0.1mm) had the least (3.70–8.89gkg−1) TOC content in the 0–15cm soil layer. The application of FYM either alone or in combination with inorganic fertilizers significantly increased the accumulation of TOC in all aggregate fractions over control, however, the effect was more pronounced in macroaggregates fraction 5–2mm and microaggregate fraction 0.1–0.053mm. The combined application of inorganic fertilizers and FYM resulted in an increase in total N content which ranged from 0.43 to 1.0gkg−1 in 5–2mm and from 0.09 to 0.44gkg−1 in 0.25–0.1mm aggregate fractions. The highest C:N ratio was recorded in aggregate fraction of 0.1–0.053mm irrespective of treatment, whereas aggregate fraction of 0.5–0.25mm had the least C:N ratio. A higher C:N ratio was observed in 15–30cm than 0–15cm soil layer. Hence it was concluded that the long-term application of FYM resulted in C and N accumulation in bulk soil and aggregates, but the accumulation pattern was dependent on aggregate size.

Can occurrence of soil hydrophobicity promote the increase of aggregates stability?

Abstract The soil hydrophobicity can be understood as soil water repellency or difficulty in wetness. This phenomenon is associated with the covering soil particles and hydrophobic organic compounds reducing the soil sorptivity and hence infiltration of water. The objectives of this study were to determine the level of hydrophobicity in the soil and assess its relationship with resistance and size distribution of water stable aggregates, particle size distribution and organic matter content of different soils in southern Brazil. Undisturbed soil samples were collected in different soil layers, 0–5, 5–10 and 10–20 cm, to determine soil sorptivity, geometric mean diameter and aggregate stability index while granulometric composition and organic matter content were determined using disturbed soil samples. The sorptivity test was conducted using a tension micro-infiltrometer, with two different liquids, distilled water and ethanol (95% v/v). The proportions of sand, silt and clay did not correlate significantly with the occurrence of hydrophobicity. In the hydrophobic soils, hydrophobicity index is directly associated with high organic matter contents and did not correlate with the particle size distribution. For the hydrophobic aggregates, cohesive forces between the particles acted for long period as a result of slow wetting, which led to an increase in geometric mean diameter, stability index of water stable aggregates and consequently greater resistance to the disintegrating actions of associated agents.

耕作方式和秸秆还田对华北地区农田土壤水稳性团聚体分布及稳定性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 耕作方式和秸秆还田对华北地区农田土壤水稳性团聚体分布及稳定性的影响 DOI: 10.5846/stxb201207261062 作者: 作者单位: 作物生物学国家重点实验室,山东省水稻研究所,作物生物学国家重点实验室,作物生物学国家重点实验室,作物生物学国家重点实验室,作物生物学国家重点实验室,作物生物学国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家“十二五”科技支撑资助项目（2012BAD14B07，2011BAD21B06）；公益性行业（农业）科研专项经费资助项目（201103001）；国家自然科学基金资助项目（30900876，31101127）；山东省农业重大应用技术创新课题资助项目 Effects of different tillage and straw systems on soil water-stable aggregate distribution and stability in the North China Plain Author: Affiliation: Agronomy College of Shandong Agricultural University,State Key Laboratory of Crop Biology,Taian Shandong 271018,Institute of Rice, Shandong Academy of Agriculture Science,Agronomy College of Shandong Agricultural University,State Key Laboratory of Crop Biology,Taian Shandong 271018,Agronomy College of Shandong Agricultural University,State Key Laboratory of Crop Biology,Taian Shandong 271018,Agronomy College of Shandong Agricultural University,State Key Laboratory of Crop Biology,Taian Shandong 271018,Agronomy College of Shandong Agricultural University,State Key Laboratory of Crop Biology,Taian Shandong 271018,Agronomy College of Shandong Agricultural University,State Key Laboratory of Crop Biology,Taian Shandong 271018 Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于10a耕作措施的定位试验，利用湿筛法研究了不同耕作措施和秸秆还田条件下农田土壤水稳性团聚体的分布规律，并利用平均重量直径（MWD）和几何平均直径（GMD）评价了不同处理水稳性团聚体的稳定性。研究结果表明，不同耕作措施处理的水稳性团聚体在0-10cm，10-20cm和20-30cm土层表现出不同的分布趋势，随着土层的加深，各处理水稳定团聚体的分布呈粒径逐渐减小、分布范围逐渐扩大趋势，0-10cm土层的水稳性团聚体多集中于2-5mm粒径范围，10-20cm土层水稳性团聚体多集中在0.5-5mm粒径范围，以0.5-1mm最多，而20-30mm，则广泛分布在0.25-5mm粒径范围。通过MWD和GMD值可以看出，免耕、耙耕和旋耕措施更能有效地保护表层（0-10cm）土壤水稳定团聚体的稳定性，常规耕作和深松处理则显著降低了20-30cm水稳性团聚体稳定性。秸秆还田显著增加了土壤有机碳（SOC）含量，且显著影响了土壤表层水稳性团聚体的稳定性。作用力分析结果表明，在0-10cm表层，秸秆作用在土壤表层显著影响了水稳定大团聚体的数量及其稳定性（P < 0.001），多元回归分析说明其与土壤有机碳含量达到了极显著水平（P < 0.01），且同时也受到来自耕作和秸秆交互效应的影响（P < 0.01）；但在10-20cm土层，影响其数量分布的主要因素是不同的耕作措施及耕作和秸秆的交互效应（P < 0.001）；而在20-30cm，耕作措施、秸秆和两者的交互效应共同对水稳性大团聚体数量产生重要的影响，但主要作用力来自耕作措施（P < 0.001）和两者的交互效应（P < 0.001）。免耕秸秆还田措施能显著提高土壤的水稳性团聚体的比例和稳定性。 Abstract:Tillage and crop residue input are two important factors to effect on the distribution and stability of soil water-stable aggregation. The objective of this study was to evaluate the changes of soil water-stable aggregate distribution and stability after 10 years in response to long-term tillage and crop straw management experiment in winter wheat (Triticum aestivum Linn.) and maize (Zea mays L.) cropping system in the North China Plain. The experiment was laid out in a split-plot design, the main plots involved five tillage systems, which included no-till (NT), subsoiling (ST), harrow tillage (HT) and rotary tillage (RT), with the conventional tillage (CT) as the control; the subplots involved two residue management methods: straw returning (P) or straw removal (A). As a result, the distributions of soil water-stable aggregate revealed varied characters in the 0-10 cm, 10-20 cm and 20-30 cm layers under the different tillage and straw management treatments. The size class of soil water-stable aggregate decreased with the soil layers deepening, while the distribution range were increased, the main ranges in the 0-10 cm, 10-20 cm and 20-30 cm layers were 2-5 mm, 0.5-5 mm and 0.25-5 mm size classes, respectively. Suitable tillage combination with crop straw input increased the proportion and stability of water-stable macro-aggregate. The proportion and stability of water-stable macro-aggregate in the 0-10cm under the PS, PR, PH and PN treatments were significant higher than that of the straw removal treatments (P < 0.05), and they significant related with the straw input (P < 0.001) and the interaction between it and tillage (P < 0.01). Meanwhile, the stability of water-stable macro-aggregate also correlated with the soil organic carbon (SOC) content of these straw returning treatments according to the multiple regression analysis (P < 0.01). Crop straw input significant increased the content of SOC and more SOC accumulated at the top of soil under conservational tillage methods such as under PS, PR, PH and PN, their contents significant higher than that of AS, AR AH and AN, respectively, this result further impacted on the stability of aggregate in different treatments in the 0-10 cm layer, but the SOC level did not influence on the stability in the 10-20 cm and 20-30 cm layers. The highest proportions in the 10-20 cm and 20-30 cm layers were observed at the PS treatment, the main driving factor of this result in the 10-20 cm layer were the tillage (P < 0.001) and the interaction between tillage and straw (P < 0.001), while in the 20-30 cm layer were the straw (P < 0.001) and the interaction between tillage and straw (P < 0.001). No tillage combination with crop straw input could improve the proportion and stability of water-stability aggregate. 参考文献 相似文献 引证文献

Effects of field managements for soil organic matter stabilization on water-stable aggregate distribution and aggregate stability in three agricultural soils

The effect of different soil organic matter (SOM) managements on soil aggregate stability was evaluated in three agricultural sites in Italy. The field plots were treated with traditional deep tillage, minimum tillage, green manuring, mature compost, and iron-porphyrin as a biomimetic catalyst. Although the original soil texture exerted a strong influence on the overall soil physical quality, after 3years of field experiments, the soil additions with humified compost, under maize cropping, improved both, the yield of water stable macroaggregates and the soil aggregate stability, with a pronounced effect on the aggregate distribution of the coarse textured soil. Soil treatments with the biomimetic catalyst, under wheat cropping, promoted an initial stable incorporation of finer particle-sizes in water-stable macro-aggregates. This effect was progressively lost with increasing experimental time due to either loss or inactivation of the catalyst. Innovative management practices for SOM stabilization based on soil amendment of either humified mature compost or a water-soluble catalyst to promote in-situ photopolymerization of humic molecules, were found to improve distribution and stability of soil water stable aggregates, as compared to the conventional methods of SOM management.

Physical Properties of an Alfisol Under Biofuel Crops in Ohio

There is an increasing need to develop renewable energy sources from biofuel crops to replace fossil fuels. Biofuel crops may also enhance ecosystem functions such as soil quality, water availability, and nutrient reserves. Therefore, the effects of four biofuel crops (corn (Zea mays), switchgrass (Panicum virgatum), indiangrass (Sorghastrum nutans) and willow (Salix spp.) were evaluated on soil quality at three sites in Ohio to assess the effects of crop species on soil bulk density (ρb), soil moisture characteristics (SMC), water stable aggregate distribution (WSA), and aggregate tensile strength (TS) to 40 cm depth. Overall, results were site-specific, with most differences occurring for the clayey soil at the Northwest site. At the Jackson site, soil in the 0-10 cm layer under switchgrass had a higher moisture content (θ) between 0 and 100 kPa than that under indiangrass. At the Western site, θ under corn at 1500 kPa was higher at 30-40 cm depth. At the Northwest site, soils under corn in the 0-10 cm depth tended to have the lowest θ at 0 and 3 kPa, while soils under switchgrass and willow had 50% more large macroaggregates and fewer small microaggregates than that under corn. Soil TS in the 0-10 cm depth under corn was nearly 160% more than that under other perennial crops. These results suggest that management of perennial biofuel crops can improve soil physical quality. Changes over seven years occur first in the surface soil layers, but further differences may evolve in subsoil layers with increase in time.

Agregação de um argissolo sob pomar de goiabeiras após aplicação de resíduos da indústria processadora de goiaba

A utilização de resíduos da indústria de processamento de frutas na agricultura pode proporcionar melhorias à qualidade do solo. Dessa forma, objetivou-se com este estudo avaliar o efeito da aplicação de resíduos de sementes de goiaba na agregação e no estoque de carbono orgânico do solo (EC). O experimento esteve inserido em um pomar comercial irrigado de goiabeiras (cv. Paluma), com sete anos de idade, sobre um Argissolo Vermelho-Amarelo distrófico típico. O delineamento experimental foi em blocos casualizados e parcelas subdivididas, sendo cinco tratamentos (doses de: 0;9;18;27 e 36 Mg ha-1 de resíduo) e duas camadas de solo (0-0,10 e 0,10-0,20 m). Foi avaliado o mesmo tipo de solo sobre mata nativa adjacente à área experimental. As análises realizadas foram a distribuição do tamanho dos agregados estáveis em água, o diâmetro médio ponderado, o diâmetro médio geométrico, os agregados maiores que 2 mm e o EC. Os dados foram submetidos à análise de variância (Teste F), seguindo o delineamento em blocos casualizados com parcelas subdivididas (5 doses x 2 camadas). As médias dos tratamentos foram comparadas pelo teste de Tukey, a 5% de probabilidade, e as médias das camadas foram comparadas pelo teste F, a 5% de probabilidade. Os dados coletados no solo sob mata foram utilizados apenas como referência de um solo em estado natural e, portanto, não foram considerados como fator de variação nas análises de variância. Os valores dos índices de agregação com o estoque de carbono orgânico do solo foram submetidos à correlação de Pearson (p &lt; 0,05). O efeito das doses de resíduo de sementes de goiaba sobre o estoque de carbono orgânico, na camada de 0-0,20 m do solo, foi avaliado por análise de regressão. Os tratamentos não diferiram em relação à agregação do solo, contudo EC foi diretamente relacionado à quantidade de resíduo aplicado ao solo. Houve correlação positiva e significativa entre os índices de agregação e o EC. A aplicação de resíduos de sementes de goiaba proporcionou melhoria da qualidade do solo.

Effects of Long-Term Fertilization on the Distribution of Carbon, Nitrogen and Phosphorus in Water-Stable Aggregates in Paddy Soil

Abstract We investigated the size distribution of water-stable aggregates and the soil carbon, nitrogen and phosphorus concentration over aggregate size fractions based on a long-term (1990-2006) fertilization experiment in a reddish paddy soil. The results showed that the largest water-stable aggregate (WSA) (>5 mm) and the smallest WSA (<0.25 mm) took up the first largest proportion (38.3%) and the second largest proportion (23.3%), respectively. Application of organic materials increased the proportion of the large WSA (>2 mm) and decreased the proportion of the small WSA (<1 mm), resulting in an increase in the mean weight diameter of WSA, whereas application of chemical fertilizer had little effect. Application of organic materials, especially combined with chemical fertilizers, increased total carbon, nitrogen and phosphorus concentrations in all sizes of WSA, and total carbon, nitrogen and phosphorus were prone to concentrate in the large WSA. Further more, application of organic materials improved the supply effectiveness of available phosphorus, whereas had little influence on the labile carbon in WSA. Application of chemical fertilizers improved concentrations of total and available phosphorus in all sizes of WSA, whereas had little influence on total carbon and nitrogen contents. Economical fertilization model maintained the soil fertility when compared with full dose of chemical fertilizers, indicating that using organic materials could reduce chemical fertilizers by about one third.

Carbono total e δ13C em agregados do solo sob vegetação nativa e pastagem no bioma cerrado

Diferentes sistemas de uso e manejo alteram o teor de carbono no solo (C), porém diminuições no C do solo têm sido reportadas quando áreas de Cerrado nativo são convertidas em pastagem. Disso resulta a necessidade da realização de pesquisas em diferentes sistemas e condições edafoclimáticas, a fim de elucidar as tendências encontradas. O objetivo deste trabalho foi avaliar a agregação, os teores de C e a abundância natural de δ13C do solo em uma área cultivada há nove anos sob lavoura seguida de 20 anos sob pastagem, a qual atualmente apresenta sinais de degradação (PA), comparando-a a uma vegetação nativa no bioma Cerrado (CE) que ocorre em área adjacente. As áreas de estudo estão localizadas no município de Rio Verde (GO), em solo classificado como Latossolo Vermelho distrófico, de textura argilosa. Em amostras de solo coletadas nas camadas de 0-5, 5-10 e 10-20 cm de profundidade, foram determinados a distribuição de agregados estáveis em água (micro, meso e macroagregados), o diâmetro médio aritmético (DMA) e geométrico (DMG), os teores de C total e de δ13C, o tempo de residência média do C (TRM) e a fração da matéria orgânica leve livre (FLL). Os resultados indicaram que o uso sob lavoura seguido de pastagem reduziu em 21 % o estoque de C original, possivelmente devido ao menor aporte de material na FLL. O solo apresentou elevada agregação e não houve diferenças significativas entre as áreas avaliadas. No entanto, os teores de C nos macroagregados foram menores na PA em relação ao CE, enquanto nos microagregados não houve diferença entre os sistemas de uso, sugerindo, respectivamente, maior e menor sensibilidade ao manejo e menor e maior proteção do C por essas classes de agregados. Os valores de TRM e as análises isotópicas reforçaram esses resultados, mostrando, ainda, substituição de 83 % do C original durante os 29 anos de cultivo. O constante aporte de resíduos vegetais, assim como a manutenção do C no interior dos macro e mesoagregados, são importantes fatores para que ocorra o acúmulo de C nesse tipo de solo.

Effects of artificial soil surface management on changes of aggregate stability and other soil properties

Studies of size distribution, stability of the aggregates, and other soil properties are very important due to their influence on tilth, water infiltration, and nutrient dynamics and more importantly on accelerated erosion but are affected by soil surface management. Both chemical e.g. pH, organic carbon, (OC), exchangeable cations e.g. calcium (Ca), magnesium (Mg) and physical properties such as aggregate size and stability are dynamic properties, which vary in response to forces affecting soil environment. This study was carried out to have a long and detailed understanding of how artificial surface soil covering materials can protect the soil physical and chemical properties from the ravages of soil erosion. Such endeavor would allow us to make suitable modification to soil conservation practices to enhance soil stability and importantly soil productivity. Data measured for eight years on induced erosion experiments on a Ferralsol covered by artificial soil netting locally called sombrite at Campinas, Brazil, were used to examine the effects of accelerated soil erosion on soil chemical and physical properties. Each erosion plot had an area of 25 x 4 m. Four soil treatments were chosen: bare (control) and three artificially covered soils. Changes of soil properties observed in relation to aggregation were bulk density, total and aeration porosity, available water capacity and changes in soil chemical properties. From pooled data stepwise multiple regressions were done to find out the relationship of aggregate stability with pH, calcium, and organic matter. There were no significant differences (P=0.05) in mean weight diameters (MWD) and size distribution irrespective of whether samples were collected from the upper middle or lower parts of the erosion plots. There were very gradual decline in mean weight diameters (MWD) and size distribution of water-stable aggregates during the study period. Bulk density increased appreciably on bare soils but remained almost constant in artificially covered soils. However, using Duncan tests, the treatment differences were not significant (P=0.05). Non-significant correlation (P=0.05) between MWD and the soil chemical properties were observed. Coefficients of determination for pH, OC, MWD and Ca could not sufficiently assist in explaining changes in aggregate stability as a result of surface cover. Key words: artificial soil covers, soil surface management, soil properties, accelerated erosion, aggregate stability.

Impact of Land Use and Soil Fertility on Distributions of Soil Aggregate Fractions and Some Nutrients

The size distribution of water-stable aggregates and the variability of organic C, N and P contents over aggregate size fractions were studied for orchard, upland, paddy, and grassland soils with high, medium, and low fertility levels. The results showed that > 5 mm aggregates in the cultivated upland and paddy soils were 44.0% and 32.0%, respectively, less than those in the un-tilled orchard soil. Organic C and soil N in different size aggregate fractions in orchard soil with high fertility were significantly higher than those of other land uses. However, the contents of soil P in different size aggregates were significantly greater in the paddy soil as compared to the other land uses. Soil organic C, N and P contents were higher in larger aggregates than those in smaller ones. The amount of water-stable aggregates was positively correlated to their contribution to soil organic C, N and P. For orchard and grassland soils, the > 5 mm aggregates made the greatest contribution to soil nutrients, while for upland soil, the 0.25-0.053 mm aggregates contributed the most to soil nutrients. Therefore, the land use with minimum disturbance was beneficial for the formation of a better soil structure. The dominant soil aggregates in different land use types determined the distribution of soil nutrients. Utilization efficiency of soil P could be improved by converting other land uses to the paddy soil.

Long-term effect of fertilizer and manure application on soil-carbon sequestration and soil fertility under the wheat–wheat–maize cropping system in northwest China

Maintenance of soil organic carbon (SOC) is important for the long-term productivity of agroecosystems. An investigation was conducted to study the effects of long-term application of inorganic fertilizers and farmyard manure (FYM) on soil organic carbon (SOC), nitrogen, phosphorus, and potassium nutrient content, water-stable aggregate distribution, and aggregate-associated carbon in a field experiment started in 1982 in an arid region of northwest China. Application of inorganic fertilizer alone (N, NP, or NPK treatments) did not increase SOC concentrations compared with no application of fertilizers (CK) and SOC concentration was significantly reduced, by 18% on average, compared with the initial value at the beginning of the experiment. Application of imbalanced inorganic fertilizer (N and NP), especially, resulted in a significant decrease in available phosphorus and potassium nutrients at a depth of 20 cm. This indicates that long-term application of inorganic fertilizers were inadequate to maintain levels of SOC and nutrients under conventional management with no aboveground crop residues returning to the soil. Long-term application of FYM alone or combined with inorganic fertilizers (M (FYM), MN, MNPK, or MNPK treatments), however, improved SOC and total nitrogen concentrations from initial values of 12.1 and 0.76 g kg−1, respectively, to 15.46 and 1.28 g kg−1, on average, and also enhanced available nitrogen, phosphorus, and potassium concentrations by 47, 50, and 68%, respectively, during the 23-year period. Treatment with FYM resulted in a 0.48 mm greater average mean weight diameter (MWD) of aggregates and a higher percentage of macro-aggregates (>2 mm) and small macro-aggregates (2–0.25 mm) than treatment without FYM. The MWD increased with increasing SOC concentration (R 2=0.75). The SOC concentration was highest in small macro-aggregates, intermediate in macro-aggregates, and lowest in micro-aggregates (0.25–0.05 mm). Approximately 54–60% of total SOC was stored in micro-aggregates (0.25–0.05 mm) and sand+silt fractions ( 0.25 mm) after treatment with FYM. MNPK treatment had the greatest effect on improving the levels of SOC and NPK nutrients and in enhancing the formation and stability of macro-aggregates.

No-tillage and manure applications increase aggregation and improve nutrient retention in a sandy-loam soil

Soil aggregation plays a crucial role in soil physicochemical and biological processes, thus influencing soil nutrient retention. It is possible to improve soil aggregation by choosing appropriate agricultural practices. The objective of this study was to evaluate the effects of tillage, crops and fertilizer sources on size distribution of water-stable aggregates (WSA) and nutrient concentrations in aggregate fractions. Soil samples were collected from field sites involving sixteen factorial combinations of tillage [conventional tillage (CT) or no-till (NT)], crop rotations [continuous maize (CC) or soybean/maize (SC)] and fertilizer sources (0, 15, 30 and 45 Mg wet weight ha − 1 of composted cattle manure balanced with inorganic fertilizers). Aggregate fractionation was performed using a wet-sieving method. Four years after the treatments were established, the proportion of large WSA (WSA > 2 mm ) was greater in the NT system, suggesting that NT increased soil aggregation compared to the CT system. There was no difference in soil aggregation between continuous maize and soybean/maize rotations. The application of 30 and 45 Mg ha − 1 year − 1 of composted manure produced more WSA > 2 mm than inorganic fertilizers. The WSA > 2 mm had a higher total C concentration in CT than NT soils, indicating that WSA > 2 mm formed in CT systems contained more soil organic matter (SOM) than those in NT systems. However, the difference disappeared when the data were expressed on a sand-free aggregate basis, indicating a dilution effect due to more sand in WSA > 2 mm from the NT system than the CT system. Total C, N and P concentrations were at least 3 times higher in water-stable microaggregates (WSA 0.25–0.053 mm) than water-stable macroaggregates (WSA > 0.25 mm ). The WSA 0.25–0.053 mm fraction is considered to be a sink for these nutrients, but may also be susceptible to erosion. Transport processes that preferentially remove the WSA 0.25–0.053 mm fraction from agroecosystems could lead to nutrient loading in adjacent ecosystems. It was concluded that adopting no-tillage and applying composted manure increased soil aggregation and nutrient retention in a sandy-loam soil under maize production.

Tillage impacts on aggregate stability and crop productivity in a loam soil of a dryland in Turkey

Seedbed preparation is important for uniform crop emergence, plant growth and high yield under different soil and climatic conditions for any crop in drylands. A three-year study (2001–2003) was conducted to investigate the effects of three tillage systems on planting performance, aggregate properties, and crop yield of a loam soil (typic Xerofluvent) with a rotation system (sunflower (Helianthus annuus L.)-barley (Hordeum vulgare L.)-Hungarian vetch (Vicia pannonica Crantz) and triticale. Tillage treatments were chisel ploughing, chisel ploughing and disc harrowing, and chisel ploughing and combine harrowing. Planting performance was determined only for sunflower. The emergence percentage of seeds sown, the percentage of plants which have an acceptable seedling interval, the percentage of gaps, and the percentage of double seedlings were used as the characteristics of planting performance. The highest percentage of gaps was in the chisel ploughing treatment, and the highest percentage of double seedlings was in the chisel ploughing and combine harrowing treatment. The percentage of gaps was reduced, and the percentage of double seedlings was increased by secondary tillage operations. Soil samples were taken from 0–20 cm depth at four different periods of the experiment. A wet-sieving method was used to determine aggregate size distribution and mean weight diameter as indices of soil aggregate stability. The percentage of water-stable aggregates for the three tillage systems was not significantly different in all size classes. Data showed significant differences among the effects of time on water-stable aggregates and. The distribution of water-stable aggregates revealed that chisel ploughing and combine harrowing treatment caused an increase in the susceptibility of macroaggregates. While there was no difference among treatments for sunflower yield, barley and Hungarian vetch and triticale yields were lower in the chisel ploughing treatment. It is not recommended to dispense with secondary tillage operations in dry conditions, owing to the limited changes in aggregation among tillage systems and higher Hungarian vetch and triticale yields.

Effects of liming on void space and aggregation in an upland grassland soil

The aim of this paper is to study changes in water-stable aggregation and void space in an upland grassland soil following a surface application of calcium carbonate intended to increase the diversity of soil fauna. Samples of the H and Ah horizons were collected at the time of the first lime application (June 1999) and 1 and 2 years thereafter. Void space in both horizons was quantified by image analysis of thin sections and the size distribution of water-stable aggregates in the Ah horizon was determined by laser granulometry. The effect of liming was largely seen in the H horizon where pH in CaCl 2 increased from 3.4 to 4.1. Percentage void space and % voids >1000 μm 2 increased significantly in the H horizon between 1999 and 2001, and there was a significant liming effect. In the mineral Ah horizon, only the change in void space over time was statistically significant. There were no significant differences in aggregate stability following liming or over time, despite a significant reduction in organic carbon concentration between 1999 and 2001. The change in void space with liming was consistent with reported changes in the abundance of larger enchytraeid genera such as Fridericia and with changes in earthworm abundance. Changes in void space with time may be linked to the cessation of grazing at the experimental site.

Influence of dry–wet cycles on the interrelationship between aggregate, particulate organic matter, and microbial community dynamics

Aggregate dynamics and their relationship to the microbial community have been suggested as key factors controlling SOM dynamics. Dry–wet (DW) cycles are thought to enhance aggregate turnover and decomposition of soil organic matter (SOM), particularly in tilled soils. The objective of this study was to evaluate the effects of DW cycles on aggregate stability, SOM dynamics, and fungal and bacterial populations in a Weld silt loam soil (Aridic Paleustoll). Samples, taken from 250 μm sieved air-dried soil (i.e. free of macroaggregates > 250 μm), were incubated with 13C-labeled wheat residue. In one set of soil samples, fungal growth was suppressed using a fungicide (Captan) in order to discern the effect of dry–wet cycles on fungal and bacterial populations. Aggregate formation was followed during the first 14 d of incubation. After this period, one set of soil samples was subjected to four DW cycles, whereas another set, as a control, was kept at field capacity (FC). Over 74 d, total and wheat-derived respiration, size distribution of water stable aggregates and fungal and bacterial biomass were measured. We determined native and labeled C dynamics of three particulate organic matter (POM) fractions related to soil structure: the free light fraction (LF), and the coarse (250–2000 μm) and fine (53–250 μm) intra-aggregate POM fraction (iPOM). In the fungicide treated soil samples, fungal growth was significantly reduced and no large macroaggregates (> 2 mm) were formed, whereas without addition of fungicide, fungi represented the largest part of the microbial biomass (66%) and 30% of the soil dry weight was composed of large macroaggregates. During macroaggregate formation, labeled free LF-C significantly decreased whereas labeled coarse iPOM-C increased, indicating that macroggregates are formed around fresh wheat residue (free LF), which is consequently incorporated and becomes coarse iPOM. The first drying and wetting event reduced the amount of large macroaggregates from 30 to 21% of the total soil weight. However, macroaggregates became slake-resistant after two dry-wet cycles. Fine iPOM-C was significantly lower in soil after two dry–wet cycles compared to soil kept at FC. We conclude that more coarse iPOM is decomposed into fine iPOM in macroaggregates not exposed to DW cycles due to a slower macroaggregate turnover. In addition, when macroaggregates, subjected to dry–wet cycles, became slake-resistant (d 44) and consequently macroaggregate turnover decreased, fine iPOM accumulated. In conclusion, differences in fine iPOM accumulation in DW vs. control macroaggregates are attributed to differences in macroaggregate turnover.