An improved method for measurement of soil aggregate stability using laser granulometry applied at regional scale

Laboratory‐based aggregate stability (AS) tests should be applied to material wetted to a moisture content comparable with that of a field soil. We have improved our original laser granulometer (LG)‐based AS test published in this journal by including a pre‐wetting stage. Our method estimates disaggregation reduction (DR; µm) for a soil sample (1–2‐mm diameter aggregates). Soils with more stable aggregates have larger DR values. We apply the new technique to soils from 60 cultivated sites across eastern England, with ten samples from each of six different parent material (PM) types encompassing a wide range of soil organic carbon (SOC) concentrations (1.2–7.0%). There are large differences between the median DR values (rescaled to < 500 µm) for soils over the PM types, which when used as a predictor (in combination with SOC concentration) accounted for 53% of the variation in DR. There was no evidence for including an interaction term between PM class and SOC concentration for the prediction of DR. After applying the aggregate stability tests with the 60 regional soil samples, they were stored for 9 months and the tests were repeated, resulting in a small but statistically significant increase in DR for samples from some, but not all, PM types. We show how a palaeosol excavated from a site in southern England can be used as an aggregate reference material (RM) to monitor the reproducibility of our technique. It has been suggested that soil quality, measured by critical soil physical properties, may decline if the organic carbon concentration is less than a critical threshold. Our results show that, for aggregate stability, any such thresholds are specific to the PM.     

SOIL ORGANIC CARBON STOCK AND FRACTIONS IN RELATION TO LAND USE AND SOIL DEPTH IN THE DEGRADED SHIWALIKS HILLS OF LOWER HIMALAYAS

The proportional differences in soil organic carbon (SOC) and its fractions under different land uses are of significance for understanding the process of aggregation and soil carbon sequestration mechanisms. A study was conducted in a mixed vegetation cover watershed with forest, grass, cultivated and eroded lands in the degraded Shiwaliks of the lower Himalayas to assess land‐use effects on profile SOC distribution and storage and to quantify the SOC fractions in water‐stable aggregates (WSA) and bulk soils. The soil samples were collected from eroded, cultivated, forest and grassland soils for the analysis of SOC fractions and aggregate stability. The SOC in eroded surface soils was lower than in less disturbed grassland, cultivated and forest soils. The surface and subsurface soils of grassland and forest lands differentially contributed to the total profile carbon stock. The SOC stock in the 1.05‐m soil profile was highest (83.5 Mg ha⁻¹) under forest and lowest (55.6 Mg ha⁻¹) in eroded lands. The SOC stock in the surface (0–15 cm) soil constituted 6.95, 27.6, 27 and 42.4 per cent of the total stock in the 1.05‐m profile of eroded, cultivated, forest and grassland soils, respectively. The forest soils were found to sequester 22.4 Mg ha⁻¹ more SOC than the cultivated soils as measured in the 1.05‐m soil profiles. The differences in aggregate SOC content among the land uses were more conspicuous in bigger water‐stable macro‐aggregates (WSA > 2 mm) than in water‐stable micro‐aggregates (WSA < 0.25 mm). The SOC in micro‐aggregates (WSA < 0.25 mm) was found to be less vulnerable to changes in land use. The hot water soluble and labile carbon fractions were higher in the bulk soils of grasslands than in the individual aggregates, whereas particulate organic carbon was higher in the aggregates than in bulk soils. Copyright © 2012 John Wiley & Sons, Ltd.     

Soil Structural Stability and Water Retention Characteristics Under Different Land uses of Degraded Lower Himalayas of North‐West India

The lower Himalayan regions of north‐west India experienced a severe land‐use change in the recent past. A study was thus conducted to assess the effect of grassland, forest, agricultural and eroded land uses on soil aggregation, bulk density, pore size distribution and water retention and transmission characteristics. The soil samples were analysed for aggregate stability by shaking under water and water drop stability by using single simulated raindrop technique. The water‐stable aggregates (WSA) >2 mm were highest (17·3 per cent) in the surface layers of grassland, whereas the micro‐aggregates (WSA < 0·25 mm) were highest in eroded soils. The water drop stability followed the similar trend. It decreased with the increase in aggregate size. Being lowest in eroded soils, the soil organic carbon also showed an adverse effect of past land‐use change. The bulk density was highest in eroded lands, being significantly higher for the individual aggregates than that of the bulk soils. The macroporosity (>150 µm) of eroded soils was significantly (p < 0·05) lower than that of grassland and forest soils. The grassland soils retained the highest amount of water. Significant (p < 0·05) effects of land use, soil depth and their interaction were observed in water retention at different soil water suctions. Eroded soils had significantly (p < 0·05) lower water retention than grassland and forest soils. The saturated hydraulic conductivity and maximum water‐holding capacity of eroded soils were sufficiently lower than those of forest and grassland soils. These indicated a degradation of soil physical attributes due to the conversion of natural ecosystems to farming system and increased erosion hazards in the lower Himalayan region of north‐west India. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigating the effects of wettability and pore size distribution on aggregate stability: the role of soil organic matter and the humic fraction

Soil organic matter (SOM) is an important factor influencing aggregate stability. Interactions between SOM and soil structure are widely studied, although the subtle relationship between SOM content, pore size distribution and aggregate stability is not fully known. Here we investigate such a relationship by means of a long‐term experiment established in 1962 in northeastern Italy, which considers different fertilizer practices (organic, mineral and mixed) applied to a continuous maize crop rotation. We measured wet stability of 1–2 mm aggregates subjected to different pretreatments. Both soil physical properties (such as pore size distribution and hydrophobicity) and chemical properties (soil organic and humic carbon content) affecting aggregate stability were considered. The chemical structure of humic substances was characterized by thermal and spectroscopic analyses (TG‐DTA, DRIFT and ¹H HR MAS NMR). The Pore‐Cor network model was then applied to evaluate the contribution of hydrophobicity and porosity to aggregate wetting. Our study suggests that SOM and its humic fraction can affect aggregate wetting and consequently slaking by modifying the pore size distribution with a shift from micropores (5–30 µm) and mesopores (30–75 µm) to ultramicropores (0.1–5 µm); hydrophobicity was also increased as a result of different humic composition. Spectroscopic analysis showed that hydrophobic compounds were mostly associated with complex humic molecules. Models of fast wetting dynamics, however, suggest that the contribution that hydrophobicity makes to aggregate stability, especially to soils with large carbon inputs, may not be the most significant factor.     

A comparison of two methods for the isolation of free and occluded particulate organic matter

Various methods exist for the isolation of particulate organic matter (POM), one of the soil‐organic‐matter (SOM) fractions reacting most sensitive on land‐use or soil‐management changes. A combination of density separation and ultrasonic treatment allows to isolate two types of POM: (1) free POM and (2) POM occluded in soil aggregates. POM fractions are closely linked to their biochemical function for the formation and stabilization of aggregates, therefore methods using different aggregate sizes may result in different POM fractions isolated. We evaluated two physical fractionation procedures to reveal whether they yield different POM fractions with respect to amount and composition, using grassland and arable soils with sandy‐loam to sandy–clay‐loam texture and thus low macroaggregate stability. Method I used air‐dried aggregates of <2.0 mm size and a low‐energy sonication for aggregate disruption, method II used field‐moist aggregates <6.3 mm and a high‐energy–sonication procedure for aggregate disruption. POM fractions were analyzed by elemental analysis (C, N) and CPMAS ¹³C‐NMR spectroscopy. With both methods, about similar proportions of the SOM are isolated as free or occluded POM, respectively. The free‐ and occluded‐POM fractions obtained with method I are also rather similar in C and N concentration and composition as shown by ¹³C‐NMR spectroscopy. Method II isolates a free‐ and occluded‐POM fraction with significantly different C and N concentrations. NMR spectra revealed significant differences in the chemical composition of both fractions from method II, with the occluded POM having lower amounts of O‐alkyl C and higher amounts of aryl C and alkyl C than the free POM. Due to the use of larger, field‐moist aggregates with minimized sample pretreatment, two distinctly different POM fractions are isolated with method II, likely to be more closely linked to their biochemical function for the formation and stabilization of aggregates. High‐energy sonication as in method II also disrupts small microaggregates <63 µm and releases fine intraaggregate POM. This fraction seems to be a significant component of occluded POM, that allows a differentiation between free and occluded POM in sandy soils with significant microaggregation. It can be concluded, that microaggregation in arable soils with sandy texture is responsible for the storage of a more degraded occluded POM, that conversely supports the stabilization of fine microaggregates.     

A new approach to determining water stable aggregation

Abstract

A new method is introduced to measure water stability of soil aggregates. The wrist‐action shaker is a simple, inexpensive tool that provides highly accurate data for the assessment of soil erodibility. Three soils from Hawaii (two Oxisols and one Vertisol) with different mineralogies, management histories, and potassium (K)‐factors were examined in this study. Six indices of water stable aggregation were determined after rapid immersion of air‐dry aggregates, followed by gentle wet‐sieving. Single‐sieve indices of percent water stable aggregates (WSA) < 0.063 mm, > 0.25 mm, and > 1.00 mm, were highly correlated. Additionally, these indices were highly correlated with three multiple sieve indices, namely geometric mean aggregate diameter (GMAD), arithmetic mean aggregate mass diameter (MAMD), and the coarse‐to‐fine index (CFI = % WSA > 1.00 mm / % WSA < 0.063 mm). Analysis of WSA data indicated that the relative soil erodibility ranking, from high to low, would be: Lualualei Vertisol > Molokai Oxisol > Kaneloa Oxisol. Discriminant analysis using GMAD and % WSA > 1.00 mm correctly classified 55 of 56 soil samples into their respective soil series.     

祁连山区主要植被类型下土壤团聚体变化特征

土壤团聚体是反映土壤结构稳定性、肥力和质量状况的重要指标,与侵蚀过程、水土流失、环境质量密切相关,研究土壤的理化性质,对保护土壤资源、提高生产率、维护土壤生态系统平衡具有重要意义。以青藏高原北缘的祁连山区为研究对象,采集该区4种主要植被类型——荒漠、草原、草甸及灌丛的土壤,分析了不同植被类型的土壤团聚体指标,水稳定性团聚体质量百分数(percentage of water-stable aggregates,WSA)、平均质量直径(mean weight diameter,MWD)、几何平均直径(geometric mean diameter,GMD)、结构体破坏率(aggregate destruction rate,PAD)、平均重量比表面积(mean weight soil specific area,MWSSA)和分形维数随海拔高度和土壤深度的变化趋势。结果表明:0~30 cm土层WSA、MWD、GMD、MWSSA依次:荒漠<草原<草甸<灌丛,>30~40 cm土层植被类型对团聚体无显著影响(P>0.05);随土壤深度的增加,土壤团聚体稳定性和团聚度逐渐降低,土壤结构趋于恶化,草甸带表层土壤团聚体稳定性显著高于深层土壤(P<0.05);随海拔高度增大,在海拔1692~2800 m土壤团聚体逐渐稳定,土壤结构改善,在海拔2800~3639 m土壤团聚体稳定性逐渐降低,土壤结构趋于恶化。WSA、MWD和GMD受1~4 mm粒级主导作用,分形维数主要受0.038~0.25 mm粒级的影响,MWSSA不能准确分析该地区的团聚体水稳性。     

季节性冻融对色季拉森林土壤团聚体稳定性的影响

为分析季节性冻融对土壤团聚体稳定性的影响,以藏东南色季拉山森林土壤为研究对象,通过野外控制性试验利用湿筛法测定团聚体组成,分析了0—10 cm, 10—20 cm, 20—30 cm深度土层各粒径团粒结构变化,以及土壤含水量(SWC),0.25 mm水稳性团聚体含量(WSA)、平均质量直径(MWD)、平均几何直径(GMD)、分形维数D、可蚀性K值各指标之间的关系。结果表明：(1)季节性冻融导致大团粒含量减少,小团粒含量增加,土壤结构失调。(2)含水量是影响团聚体稳定性的重要因素之一。(3)季节性冻融作用整体上导致MWD,GMD变小,D值与K值变大,降低了土壤团聚体稳定性。(4)当土壤冻融次数在一定范围内STF-One中,WSA有所增加,土壤稳定性有所增强。(5)土壤团聚体WSA,MWD和GMD均与D值和K值呈负相关。(6)在SFT-Ys类型土壤中土壤结构变化,0.5 mm粒级是重要临界点。综上,研究为季节性冻融对土壤稳定性的影响提供数据支持,为冻土潜在受侵蚀情况提供理论依据。     

Clay mineralogy differs qualitatively in aggregate‐size classes: clay‐mineral‐based evidence for aggregate hierarchy in temperate soils

Clay minerals have a major role in soil aggregation because of their large specific surface area and surface charges, which stimulate interactions with other mineral particles and organic matter. Soils usually contain a mixture of clay minerals with contrasting surface properties. Although these differences should result in different abilities of clay minerals regarding aggregate formation and stabilization, the role of different clay minerals in aggregation has been seldom evaluated. In this study, we took advantage of the intrinsic mineral heterogeneity of a temperate Luvisol to compare the role of clay minerals in aggregation. First, grassland and tilled soil samples were separated in water into aggregate‐size classes based on the aggregate hierarchy model. Then, clay mineralogy and organic C in the aggregate‐size classes were analysed. Interstratified minerals containing swelling phases accumulated in aggregated fractions compared with free clay fractions under the two land‐uses. The accumulation increased with decreasing aggregate size from large macroaggregates (> 500 µm) to microaggregates (50–250 µm). Carbon content and carbon‐to‐nitrogen ratio followed the opposite trend. This fully supports the aggregate hierarchy model, which postulates an increasing importance of mineral reactivity in smaller aggregates than in larger aggregates in which the cohesion relies mostly on physical enmeshment by fungal hyphae or small roots. Consequently, differences in the proportion of the different 2:1 clay minerals in soils can influence their structure development. Further research on the links between clay mineralogy and aggregation can improve our understanding of mechanisms of soil resistance to erosion and organic matter stabilization.     

Organic Carbon Dynamics along a Toposequence in a Peri‐urban Site

Abstract

The pattern of carbon (C) storage in soils has implications for agriculture and the environment. Dynamics of organic C, in the 0‐ to 20‐cm soil depth along a toposequence in a peri urban site in Sierra Leone, West Africa, were studied. Organic C was determined by the dry‐combustion method on the following aggregate size fractions: whole soil (<2000 µm), 250–2000 µm, 53–250 µm, and <53 µm.

Mean organic C content of whole soil ranged from 4.8% on the backslope to 9.3% on the toeslope. Organic C content of aggregate size fractions increased with decreasing aggregate size. The amount of soil and organic C present in aggregate size fractions, at all positions on the toposequence, decreased with decreasing aggregate size. In general, convex upper slopes had lower contents and amounts of organic C compared to lower concave areas. This study provided benchmark levels and patterns against which changes resulting from imminent urbanization can be measured.     

Aggregate breakdown dynamics under rainfall compared with aggregate stability measurements

Aggregate breakdown due to rainfall action causes crusting and interrill erosion. Erodibility is seemingly determined by the capacity of surface aggregates to resist the effects of rainfall. In this paper, we evaluated the relevance of an aggregate stability measurement, which comprises three treatments, in order to characterize aggregate breakdown dynamics. Two cultivated soils were studied: a clay loam slightly sensitive to erosion and a more susceptible silt loam. We compared the size distributions of microaggregates produced by the three aggregate stability treatments with the results from a rainfall simulation. The behaviour of four initial aggregate size classes (< 3 mm, 3–5 mm, 5–10 mm and 10–20 mm) was also compared to study the influence of the initial aggregate size on the nature of resulting aggregates. The mean weight diameter was from 200 to 1400 µm for the silt loam and from 600 to 7000 µm for the clay loam. The two experiments – aggregate stability measurements and aggregate breakdown dynamics under rainfall – yielded similar results. Qualitative analysis showed that for both soils the sizes of fragments produced by breakdown with the aggregate stability tests and under rainfall were similar and seemed to be qualitatively independent of the size of initial aggregates. We first schematized the structural organization of aggregates in cultivated horizons with a simple hierarchical model at two levels: (i) < 250 µm microaggregates and (ii) > 250 µm macroaggregates made by the binding together of microaggregates. We then developed a model of aggregate breakdown dynamics under rainfall which gives, for various rainfall durations, the size distributions of resulting fragments on the basis of aggregate stability measurements. We obtained a correlation coefficient, r, of 0.87 for the silt loam and of 0.91 for the clay loam, showing that the experimental and predicted mass percentages were linearly related for each size fraction.     

Contributions of incorporated residue and living roots to aggregate-associated and microbial carbon in two soils with different clay mineralogy

We conducted a study to investigate the role of aggregates in the stabilization of residue‐ and root‐derived C in an illitic Mollisol and a kaolinitic Oxisol under the following treatments: (i) incorporated residue, (ii) growing plants, and (iii) both incorporated residue and growing plants. Residue‐C dynamics were followed in soils incubated with ¹³C‐labelled wheat residue with and without unlabelled growing wheat plants. Root‐C was traced by growing wheat plants with and without unlabelled wheat residue in a ¹³CO₂‐labelling chamber. After 46 and 76 incubation days, residue‐ and root‐C were measured in four aggregate size classes and in microbial‐C. Both soils had greater residue‐derived than root‐derived total aggregate‐associated C at day 76, which we attributed to the larger residue‐C than root‐C inputs at the start of the experiment. On an aggregate basis, the ratio of residue‐derived over root‐derived C decreased in most size fractions over time, indicating a greater potential for longer‐term root‐C than residue‐C stabilization by aggregates in both soils. At both sampling days, all aggregates > 53 µm had greater residue‐C concentrations in the illitic soil than in the kaolinitic soil and this difference increased with increasing aggregate size. This suggested a greater affinity of illite clay than kaolinite clay to bind with fresh residue‐derived compounds into larger aggregates and hence a greater importance of aggregates in stabilizing residue‐C in illitic compared with kaolinitic soils. The stabilization of root‐C by aggregates was less affected by clay mineralogy and thus less dependent on the affinity of clay minerals to bind with root‐derived compounds.     

利用地统计学技术预测流域尺度土壤团聚体稳定性及团聚体结合有机碳含量空间分布

The association of organic carbon with secondary particles (aggregates) results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of soil water-stable aggregates (WSA), mean weight diameter (MWD) of aggregates and organic carbon (OC) content in macro- (> 2 mm), meso- (1-2 mm), and micro-aggregate (< 1 mm) fractions, using geostatistical methods. One hundred and eleven soil samples were collected at the 0-10 cm depth and fractionated into macro-, meso-, and micro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates (9 g kg?1), followed by micro-aggregates (7 g kg?1), while the least OC content was found in macro-aggregates (3 g kg?1). Although a significant e?ect (P = 0.000) of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant e?ect (P = 0.073) on aggregate OC content. The coe?cients of variation (CVs) for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable (CV = 71%). Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. The mean content of WSA ranged from 15% for macro-aggregates to 84% for micro-aggregates. Geostatistical analysis showed that the measured soil variables exhibited di?erences in their spatial patterns in both magnitude and space at each aggregate size fraction. The relative nugget variance for most aggregate-associated properties was lower than 45%. The range value for the variogram of water-stable aggregates was almost similar (about 3 km) for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about 6.5 km for meso-aggregates. Kriged maps of predicted WSA, OC and MWD for the three studied aggregate size fractions showed clear spatial patterns. However, a close spatial similarity (co-regionalization) was observed between WSA and MWD.     

Fate of airborne metal pollution in soils as related to agricultural management: 2. Assessing the role of biological activity in micro‐scale Zn and Pb distributions in A,B and C horizons

This work assesses relationships between characteristic aggregate microstructures related to biological activity in soils under different long‐term land use and the distribution and extractability of metal pollutants. We selected two neighbouring soils contaminated with comparable metal loads by past atmospheric deposition. Currently, these soils contain similar stocks, but different distributions of zinc (Zn) and lead (Pb) concentrations with depth. One century of continuous land use as permanent pasture (PP) and conventional arable (CA) land, has led to the development of two soils with different macro‐ and micro‐morphological characteristics. We studied distributions of organic matter, characteristic micro‐structures and earthworm‐worked soil by optical microscopy in thin sections from A, B and C horizons. Concentrations and amounts of total and EDTA‐extractable Zn and Pb were determined on bulk samples from soil horizons and on size‐fractions obtained by physical fractionation in water. Large amounts of Zn and Pb were found in 2–20‐µm fractions, ascribed to stable organo‐mineral micro‐aggregates influenced by root and microbial activity, present in both soils. Unimodal distribution patterns of Zn, Pb and organic C in size‐fractions were found in horizons of the CA soil. In contrast, bimodal patterns were observed in the PP soil, because large amounts of Zn and Pb were also demonstrated in stable larger micro‐aggregates (50–100‐µm fractions). Such differing distribution patterns characterized all those horizons markedly influenced by earthworm activity. Larger earthworm activity coincided with larger metal EDTA‐extractability, particularly of Pb. Hence, land use‐related biological activity leads to specific soil microstructures affecting metal distribution and extractability, both in surface and subsurface horizons.     

三峡库区坡地脐橙园保护性措施对土壤团聚体结构及碳、氮、磷含量的影响

依托三峡工程生态与环境秭归实验站的8 a长期试验,对5种保护性管理措施下坡地脐橙园土壤团聚体结构与团聚体碳、氮、磷含量分布特征进行了研究。结果表明,脐橙套种多年生白三叶草(CM)和脐橙园地面农作物秸秆覆盖(SM)处理表层土壤(0～5 cm)大于0.25 mm水稳性团聚体含量、团聚体平均重量直径(MWD)值、大于0.25 mm水稳性团聚体氮含量及SM处理表层土壤大于0.25 mm水稳性团聚体磷含量显著高于其他处理;脐橙套种黄花菜等高植物篱(CH)处理和脐橙园沿等高线埋设防渗膜(MM)处理表层土壤大于0.25 mm水稳性团聚体含量及CH处理的MWD值显著高于常规脐橙栽植(CK)和脐橙套种小麦-花生(PC)处理;与CK处理相比,PC处理大于0.25 mm水稳性团聚体含量、MWD值、团聚体碳含量和表层土壤团聚体氮含量没有显著变化,但5～20 cm土壤团聚体磷含量有升高趋势。团聚体MWD与大于0.25 mm水稳性团聚体和团聚体氮含量有极显著相关关系。     

退化花岗岩植被恢复对团聚体及其有机碳的影响

研究退化红壤不同治理措施对土壤水稳性团聚体及其有机碳的影响。结果表明,恢复林地提高了0-20cm、20-40cm土层>0.25mm水稳性团聚体(WSA)含量和平均重量直径(MWD),显著提高土壤水稳性。表土中,大体上侵蚀林地WSA含量及其有机碳含量随粒径减小而增大,恢复林地随粒径增大而增大,并向>5mm、5～2mm两粒径富集,且侵蚀地、不同年代治理的林地、次生林间差异达显著水平(P<0.05);底土中,次生林、黑荆治理的林地WSA分布及有机碳含量变化与其表层的变化趋势相似,其他林地大体上向5～2mm、1～0.5mm两粒径富集。WSA含量及密度具有表聚性,且主要取决于治理年限、治理措施。     

Nomographic estimation and evaluation of soil erodibility under simulated and natural rainfall conditions

To evaluate soil erodibility under different land uses and to study the applicability of nomograph for estimation of soil erodibility a field experiment was conducted under both natural and simulated rainfall conditions under four land uses viz. barren, cultivated, grassland, and forest in the sub‐mountainous tract of Punjab (India). Measured soil erodibility (K) values varied from 0·33 to 0·67 under natural rainfall conditions and from 0·23 to 0·40 under simulated rainfall conditions. Among different land uses, measured K was in the order of barren > cultivated > grassland > forest soils. The values of the K estimated by nomograph were very low as compared to the observed values. The trends were also in contrast to these observed values of K under simulated and natural rainfall conditions. To modify nomograph equation, different ranges of aggregate sizes were correlated with soil loss. It was observed that water stable aggregates (WSA) <2 mm size had a significant correlation with soil loss under both natural (r = 0·88) and simulated (r = 0·76) rainfall conditions. So the nomograph equation was modified to include the M parameter based on WSA <2 mm size. The value of K estimated from the modified nomograph had a significant correlation with measured values of K under both the natural and simulated rainfall conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of Artificial Zeolite and Hydrated Lime Amendments on the Erodibility of an Acidic Soil

In this study, the effectiveness of artificial zeolite and hydrated lime, as amendments, to reduce surface runoff and soil loss from acidic soil taken from Yamaguchi prefecture in Japan was assessed. Air‐dried soil aggregates (?2 mm) were amended with zeolite at 10% and with lime at 0.5%. The amended aggregates were packed to an average dry‐bulk density of 1.30 Mg m^?3 in small soil trays and subjected to simulated rain intensities of 30 and 60 mm h^?1. Two pretreatments were used before subjecting them to simulated rainfall: (a) soil incubated for 2 weeks and (b) soil kept for 5 months, irrigated every two days. The data indicated that surface runoff was characterized by three phases. The amendments' impact was most significant during the first two phases as the amendments induced the formation of particles sized ? 106 µm, which are mostly responsible for the crusting. Amendments decreased soil losses, and the magnitude of reduction became higher when the irrigation pretreatment was applied before simulated rainfall. The amendment led to increase in soil organic carbon, wet aggregate stability, saturated hydraulic conductivity, and the large particle size in the sediment. The results suggest that surface runoff and soil loss in acidic soils can be substantially reduced by application of zeolite or lime, and this is attributed to the increase in wet aggregate stability and the large particle size in the sediment because of the amendments, and in this regard zeolite is more effective than lime.