Prescribed burning effects on soil physical properties and soil water repellency in a steep chaparral watershed, southern California, USA

Chaparral watersheds associated with Mediterranean-type climate are distributed over five regions of the world. Because brushland soils are often shallow with low water holding capacities, and are on slopes prone to erosion, disturbances such as fire can adversely affect their physical properties. Fire can also increase the spatial coverage of soil water repellency, reducing infiltration, and, in turn, increasing overland flow and subsequent erosion. We studied the impacts of fire on soil properties by collecting data before and after a prescribed burn conducted during Spring 2001 on the San Dimas Experimental Forest, southern California. The fire removed the litter layer and destroyed the weak surface soil structure; leaving a thin band of ash and char on top of, and mixed in with, an unstable, granular soil of loose consistency. Median litter thickness and clay content were significantly decreased after fire while soil bulk density increased. At 7 d post-fire, soil surface repellency in the watershed was significantly higher than prior to the burn. At 76 d post-fire, surface soil water repellency was returning to near pre-fire values. At the 2 and 4 cm depths, 7 d post-fire soil repellency was also significantly higher than pre-fire, however, conditions at 76 d post-fire were similar to pre-fire values. Variability in soil water repellency between replicates within a given 15 × 15 cm site was as large as the variability seen between sites over the 1.28 ha watershed. The increase in post-fire persistence of water repellency was largest beneath ceanothus (Ceanothus crassifolius) as compared to a small increase beneath chamise (Adenostoma fasciculatum). However, pre-fire persistence was higher under chamise than for ceanothus. Post-fire changes to soil properties may increase the watershed hydrologic response, however the mosaic distribution of water repellency may lead to a less severe increase in hydrologic response than might be expected for a spatially more homogenous increase in repellency.     

Temporal variation in topsoil water repellency in two recently burnt eucalypt stands in north-central Portugal

The aim of this study is to improve our knowledge of the temporal and spatial variations of soil water repellency following wildfire, in particular for the eucalypt stands that now dominate the landscape of north-central Portugal.     

Thermal destruction of soil water repellency and associated changes to soil organic matter as observed by FTIR spectroscopy

The heat generated during wildfires often leads to increases in soil water repellency. Above a critical heating threshold, however, its destruction occurs. Although the temperature thresholds for repellency destruction are relatively well established, little is known about the specific changes in the soil organic matter that are responsible for repellency destruction. Here we report on the analysis of initially water repellent surface soil samples (Dystric Cambisol, 0–5 cm depth) by transmission Fourier Transform Infrared (FTIR) spectroscopy analysis before and after destruction of its water repellency by heating to 225 °C in order to investigate heating-induced changes in soil organic matter (SOM) composition. Although assignment of absorption bands is made difficult by overlapping of some bands, it was possible to distinguish bands relevant for hydrophobicity of SOM in the soil before heat treatment. The most significant decrease in absorbance following water repellency destruction took place in the frequency area corresponding to stretching vibrations of aliphatic structures within SOM. The results suggest that besides a general decrease of SOM content during heating, the loss of soil water repellence is primarily caused by the selective degradation of aliphatic structures.     

两种常用方法测定土壤斥水性结果的相关性研究

土壤斥水性不利于农业生产和环境的可持续性发展,引起了很多土地利用问题。为了合理地选择土壤斥水特性的测定方法,该文采用常用的滴水穿透时间法与酒精溶液入渗法两种方法测定了内蒙古锡林浩特羊草草原土壤的斥水性,并分析了两种方法的相关性。结果表明：两种方法测定的土壤斥水性具有较强的相关性,在一定范围内可以通过文中提出的多项式进行转换,并获得了中度斥水性等级以下的酒精溶液入渗法的土壤斥水性等级指标。     

Occurrence and hydrological effects of water repellency in different soil and land use types in Mexican volcanic highlands

Little is known on the hydrological behavior of the volcanic ash soils, which are characterized by extremely high porosities and hydraulic conductivities. In this study the occurrence and hydrological effects of water repellency were investigated at a plot scale for different types of land use and volcanic soils in Mexican volcanic highlands from Michoacan, Mexico: [1] fir, pine and oak mixed forest soils developed from lavas, [2] soils developed from volcanic ashes and pyroclastic sediments under sparse fir, pine and oak forest and shrubland, [3] pine and oak forested soils developed from lavas and pyroclastic sediments, and [4] bare soils on recent ash sediments in plain surfaces. Soil water repellency was assessed using the water drop penetration time test and rainfall simulations were performed on circular plots (50 cm in diameter) during 30 min and at an intensity of 90 mm h^− 1 in order to study the hydrological response of each area. The return period for storms with a similar intensity in the area is 10 years. The shape and depth of the wetting front after simulated rainfall was also analyzed. Soil water repellency showed a high variability among the different studied zones. Organic matter content, soil texture and acidity were the most important factors for developing hydrophobicity. A wide range of soil water repellency classes (hydrophilic to severely water-repellent soils) has been found in soils under dense fir, pine and oak mixed forests or shrubland, while inexistent or slight water repellency has been observed in soils under sparse forest or at bare ash-covered areas. At a plot scale, marked differences in the hydrological behavior of the studied land use and soil zones were observed after the rainfall simulations. Soil water repellency contributes to fast ponding and runoff generation during the first stages of rainstorms. Runoff was enhanced in water-repellent forested soils (average runoff coefficients between 15.7 and 19.9%), in contrast to hydrophilic or slightly water-repellent soils, where runoff rates were lower (between 1.0 and 11.7%). Shallow and irregular wetting fronts were observed at water-repellent zones, reducing the soil water storage capacity. The implications of soil water repellency in soil hydrology and erosion risk in the area shed light on the soil hydrology of the studied ecosystems, and can contribute to develop better management policies.     

Fire-induced soil water repellency under different vegetation types along the Atlantic dune coast-line in SW Spain

The distribution and variation with soil depth of water repellency has been studied in fire-affected sand dunes under three different vegetation types (pine forest, shrubland and sparse herbaceous vegetation) in SW Spain. The persistence and intensity of water repellency at the exposed surface of soil was measured using the water drop penetration time test and the contact angle method, respectively, in surface samples (0–3 cm) collected at burned and unburned areas. The variation of water repellency with depth in burned areas was studied in soil profiles every 5 cm between 0 and 40 cm depth. None or slight soil water repellency was observed at unburned soil sites, whereas burned soil sites showed a high degree of repellency, especially under pines and shrubland. The spatial pattern of fire-induced soil water repellency was found to be associated to vegetation types, although it was modulated by soil acidity and the soil organic carbon content. Soil water repellency was generally higher at the soil surface, and decreased with depth. Dense pine forests and shrublands showed strong and/or severe water repellency in depth, but it was rare and limited to the first five centimeters under sparse herbaceous vegetation. The heterogeneity of moisture patterns under dense pine forests or shrublands showed the existence of wetting and water repellent three-dimensional soil patches.     

沂蒙山区桃园棕壤斥水性对理化性质的空间响应

以沂蒙山区典型土地利用桃园棕壤为例,在分析降雨前后桃园棕壤斥水性与理化性质空间变异的基础上,探讨了棕壤斥水性对土壤含水量、有机质含量和土壤质地的空间响应特征。按照1 m×1 m网格等间距测定降雨前后土壤实际斥水性与含水量,同时采集表层0~3 cm土壤样品,分析其有机质含量与砂粒、粉粒、黏粒含量,并借助经典统计学、地统计学与空间自相关理论对土壤斥水性及理化性质进行空间格局与空间相关性分析。结果表明:沂蒙山区桃园棕壤的斥水程度强烈,雨后斥水性显著降低;降雨前后棕壤斥水性均具有中等变异水平和较强的空间自相关性,且呈指数模型分布,各向异性显著。受结构变异和随机变异作用,斥水性空间格局沿耕作方向呈条带状分布,在其垂直方向上最小变程为1.4 m。土壤质地是影响棕壤斥水性空间变异的主要因素,斥水性与粉粒含量呈空间正相关,与砂粒和黏粒含量呈空间负相关,相关程度粉粒砂粒黏粒;棕壤斥水性与含水量呈空间负相关,相关度雨前较弱,雨后显著。     

盐渍化农田土壤斥水性与理化性质的空间变异性

通过对新疆玛纳斯县盐渍化土壤三个不同尺度(间距分别为50 m、5 m及0.5 m)的284个样点取样分析测定,采用经典统计学、空间自相关、地统计学和分形理论对土壤斥水性与理化性质进行空间格局分析。结果表明:1)土壤斥水性和pH符合正态分布,其余土壤属性符合对数正态分布。三尺度下土壤各属性绝大多数表现为中等变异水平。2)三尺度下土壤各属性的Moran s I系数变化具有相似性,在-0.8~0.6范围内波动。3)三尺度下土壤各属性的半方差函数理论模型大多数能用球状模型来拟合。4)在一定范围内,土壤各属性具有一定的分形特征,分形维数变化幅度为1.75~1.96。分析表明不同尺度下土壤斥水性与理化性质具有一定的差异。     

Influence of different plant species on water repellency in Mediterranean heathland soils

It is established that soil hydrophobicity reduces soil infiltration rates, and enhances runoff flow and soil erosion. Water repellency has been studied with special interest in coniferous and eucalyptus forests, particularly after burning, but the number of studies concerning Mediterranean heathlands is still very low. In this paper, we study the occurrence and persistence of water repellency in soil samples collected under different plant species susceptible to induce soil hydrophobicity (Erica arborea, Erica australis, Calluna vulgaris, Quercus lusitanica and Rhododendron ponticum) in a natural protected area in southern Spain. Great attention has been paid to the relationships between soil water repellency and environmental factors as organic matter content and soil acidity. The largest hydrophobicity was measured in soil samples collected under E. australis, E. arborea and C. vulgaris. For these species, the organic matter content and pH showed positive and negative correlations with the persistence of water repellency, respectively. The hydrophobicity originated by humic substances in the soil seems to be the only explanation for slight soil water repellency under Q. lusitanica or R. ponticum. The patchy patterns of occurrence and persistence of soil water repellency is governed by the spatial distribution of the studied species and modulated by other factors. Soil surface water repellent layers reduce the infiltration rates and limit the water storage capacity. However, the macropore flow can be enhanced on non-repellent layers, cracks or roots such us the wetting's front shown. The vegetation effects on soil hydrology should be considered for afforestation works and flooding control.     

Soil water repellency in an old and young pasture in relation to N application

Ageing of pastures is likely to affect the degree of potential water repellency in the long term, whereas seasonal variation on a shorter term affects the actual repellency of soils. A 1-year study on two pastures of different ages was conducted on a sandy soil to assess changes in the degree of potential and actual water repellency in relation to different levels of applied nitrogen (N). Sampling was carried out on four dates (April, June, August and October) to determine soil moisture content and both potential and actual water repellency at three depths (0–25, 25–50 and 50–75 cm). The relative number of potentially wettable samples for the young pasture (5 years) ranged from 64% (0–25 cm) to 96% (25–50 cm) to 100% (50–75 cm). For the old pasture (38 years) this ranged from 29 to 66 to 94%. The transition zone in which topsoil samples could be either wettable or water repellent ranged from 18 to 23% (v/v) for the young pasture compared with a range from 29 to 32% (v/v) for the old pasture. Thus, ageing pastures may result in both moving as well as decreasing transition zones over time. A positive relationship between increased inputs of fertilizer N, higher DM yields, lower soil water contents and higher degrees of water repellency was found for the old pasture for the August series. This suggests that seasonal variation in water repellency can be further re-enforced through nutrient management.     

Water repellency and moisture content spatial variations under Rosmarinus officinalis and Quercus coccifera in a Mediterranean burned soil

Variations in the distribution pattern of soil water repellency (SWR) and soil moisture are of major importance for the hydrological and geomorphological processes in Mediterranean burned areas, and also for their ecological implications concerning to re-establishment of the vegetation cover. This paper studies the influence of Rosmarinus officinalis L. and Quercus coccifera L. vegetated patches on SWR and their relationships with soil moisture content (SMC) and soil organic matter (SOM) in burned and unburned calcareous soils of a Mediterranean shrubland ecosystem, considering the first rainfall event occurred after the wildfire in Les Useres (Castellón, eastern Spain).     

盐渍化农田土壤斥水性与理化性质的空间变异性

通过对新疆玛纳斯县盐渍化土壤三个不同尺度（间距分别为50m、5m及0.5m)的284个样点取样分析测定,采用经典统计学、空间自相关、地质统计学和分形理论对土壤斥水性与理化性质进行空间格局分析。结果表明：1）土壤斥水性和pH符合正态分布,其余土壤属性符合对数正态分布。三尺度下土壤各属性绝大多数表现为中等变异水平。2）三尺度下土壤各属性的Moran’s I系数变化具有相似性,在-0.8～0.6范围内波动。3）三尺度下土壤各属性的半方差函数理论模型大多数能用球状模型来拟合。4）在一定范围内,土壤各属性具有一定的分形特征,分形维数变化幅度为1.75～1.96。分析表明不同尺度下土壤斥水性与理化性质具有一定的差异。     

Mycelium of arbuscular mycorrhizal fungi increases soil water repellency and is sufficient to maintain water-stable soil aggregates

Using an in vitro bioreactor system in which the arbuscular mycorrhizal (AM) fungus Glomus intraradices was grown in a soil devoid of detectable living microbes, we could show that the mycelium of this fungus contributed to the maintenance of water-stable soil aggregates and increased soil water repellency, as measured by water drop penetration time. This is to our knowledge the first demonstration of a causal link between AM fungal growth and water repellency of soil aggregates. Our results also place AM fungal contributions to soil aggregation on a firm mechanistic footing by showing that hyphae are sufficient to produce effects, in the absence of other soil biota, which have always been included in previous studies.     

Effect of fire severity on water repellency and aggregate stability on Mexican volcanic soils

A field study was conducted in order to study the effects of different wildfire severities on [1] soil organic matter content, [2] soil water repellency, and [3] aggregate stability; [4] the distribution of soil water repellency in aggregate sieve fractions (1–2, 0.5–1, 0.25–0.5 and < 0.25 mm) was also studied. Five similar burned sites and two long-unburned control sites were selected under mixed fir and pine forests in volcanic highlands from Michoacán, Mexico. Soil water repellency was observed in soil samples from all sites, although changes were influenced by fire severity. Sites affected by low severity fires did not show important changes in burned soils in comparison with controls, while high severity fires caused different responses: water repellency was increased or destroyed probably due to temperatures below or above 200–250 °C during burning. The degree of wettability/repellency from the fine earth fraction of burned soils seems to be conditioned by < 0.5 mm aggregates, more than coarser aggregates which always showed a higher degree of wettability. It is suggested that destruction of organic matter during burning occurs principally in coarse aggregates, where combustion can be more intense. Aggregate stability (measured using pre-wetted aggregates between 4 and 4.8 mm) did not change under low severity burning but it was considerably reduced in the case of a high fire severity. Losses of organic matter and destruction of water repellency seem to be the reasons for that reduction in this type of soil in contrast to previous studies, where aggregate stability increased after burning. Changes in both properties (water repellency and aggregate stability) are expected to induce modifications in runoff and soil loss rates at the hillslope scale.     

Water repellency reduction using soil heating in infiltration ponds of a wastewater soil aquifer treatment (SAT)

Reuse of treated wastewater (TWW) for irrigation in agriculture is a common alternative water source in arid regions suffering from fresh water (FW) shortage. Soil aquifer treatment (SAT) is frequently used for advanced TWW purification. Infiltration rates of water through the soil can decrease as a consequence of organic matter (OM) accumulation and the consequent induction of water repellency. In this research, soil heating to high temperatures was examined for its efficiency in OM content reduction and increased infiltration. In a laboratory experiment conducted using a hand burner and a combustion oven, water repellency was found to be reduced following increased heating temperature or heating duration, directly resulting in reduction of OM level. Chemical analysis of OM extracted from the heat treated soils revealed reduction in hydrophobic substances as a consequence of increased temperatures by soil heating and heating duration. In model ponds built to simulate large infiltration basins, OM content was reduced as a result of intensive and moderate soil heating in comparison to the untreated pond. However, no reduction in water repellency and only slight changes in infiltration rate were found as a consequence of soil heating. The differences in results obtained in the laboratory and the field experiments were probably related to the fact that the soil in the field experiment has been continuously reloaded with TWW containing OM.     

水分和有机物料对镉污染土壤的改良效应

通过室内培养和盆栽试验相结合的方式,系统研究了3种土壤水分含量条件下,添加不同有机物料对镉(Cd)污染土壤的改良效应。研究结果表明:淹水、田间持水量和65%相对含水量条件下添加有机物料均有利于污染土壤中可交换态Cd含量的降低,铁锰氧化物及有机结合态Cd含量的增加。随土壤中水分含量的增加,影响程度增加,即淹水>田间持水量>65%相对含水量。3种水分条件下,添加蚯蚓粪处理Cd活性降低明显,其次为猪粪处理,草炭处理相对较差。淹水条件下,油菜体内Cd的含量最低,田间持水量和65%相对含水量条件下油菜部分发育指标差异不显著。添加不同有机物料各处理促进油菜生长的顺序大致为:蚯蚓粪>草炭>CK>猪粪。     

野葛及百喜草对红壤坡地水土保持及土壤改良的效应

试验研究红壤坡地野葛水土保持和土壤改良效应结果表明,横峰野葛和百喜草可有效增大土壤持水量、土壤孔隙度和降低土壤容重,提高土壤pH值、有机质和N、P、K含量,减少土壤侵蚀量和径流量,水土保持和改良土壤效果明显,且野葛综合效果优于百喜草。