J. Albaladejo

Factors regulating spatial distribution of soil water content in small semiarid catchments

Abstract The factors which control soil moisture patterns in a semiarid area are determined in two different locations: a burnt zone with little vegetation and an unburnt zone with a greater vegetal cover. In the burnt area, the factors affecting the spatial variability of the soil water content are those considered as local controls such as soil texture and slope. These factors are able to explain a significant part of the spatial distribution of soil moisture in this zone independently of the soil moisture state. In the unburnt area, the factors affecting soil moisture were those related with the presence or absence of vegetation in semiarid environments. The upslope contributing area, aspect, soil profile curvature and soil depth best explained the spatial variability of the soil moisture content in the vegetated zone. The actual influence of these factors showed marked seasonal variations due to changes in the physiological activity of the vegetal cover. These factors, which are in part responsible for the distribution of soil moisture, are not commonly integrated in traditional topographic wetness indices. The topographic index of Beven and Kirkby (Beven, K.J., Kirkby, M., 1979. Hydrological Sciences Bulletin 24, 43–69) is extended to account for the interstorm soil water losses. The new indices incorporating the hillslope aspect improve the prediction power of soil water content patterns in semiarid areas.

Spatial patterns and temporal stability of soil moisture across a range of scales in a semi-arid environment

The antecedent soil moisture status of a catchment is an important factor in hydrological modelling. Traditional Hortonian infiltration models assume that the initial moisture content is constant across the whole catchment, despite the fact that even in small catchments antecedent soil moisture exhibits tremendous spatial heterogeneity. Spatial patterns of soil water distribution across three transects (two in a burnt area and one in an unburnt area) in a semi-arid area were studied. At the transect scale, when the factors affecting soil moisture were limited to topographical position or local topography, spatial patterns showed time stability, but when other factors, such as vegetation, were taken into account, the spatial patterns became time unstable. At the point scale, and in the same areas, topographical position was the main factor controlling time stability. Scale dependence of time stability was studied and local topography and vegetation presence were observed to play an important role for the correlation between consecutive measures depending on the scale. Copyright

Factors influencing surface runoff generation in a Mediterranean semi-arid environment : Chicamo watershed, SE Spain

A deeper knowledge of the hydrological response of semi-arid Mediterranean watersheds would be useful in the prediction of runoff production for assessing flood risks and planning flood mitigation works. This study was conducted to identify the runoff generation mechanisms and their controlling factors at the hillslope scale in a Mediterranean semi-arid watershed. Four zero-order microcatchments were selected to measure rainfall and runoff for a three-year period. Two groups of soil were differentiated with respect to the hydrological response. The fine textured, poorly permeable soils of low organic carbon content had a greater runoff coefficient (9%) and lower runoff threshold (3·6 mm) than more permeable, coarser textured soils of medium organic carbon content ( 5 mm h−1); and (ii) a saturation-excess overland flow in the less degraded areas with a high organic carbon content (>2%), high infiltrability (>8 mm h−1) and covered by a dense plant cover (>50%).

Aggregate stability changes in a semiarid soil after treatment with different organic amendments

Structural stability of soils is one of the most important characteristics related to soil degradation in semiarid areas. Organic additions can considerably improve soil structure and prevent soil degradation. In this experiment the effectiveness was compared of four types of organic amendments on the improvement of soil structure. The four treatments are sewage sludge, fresh uncomposted urban refuse, composted urban refuse, and horse manure. The uncomposted urban refuse was the most effective in increasing soil stable aggregates. The higher doses of sewage sludge and compost also improved aggregation of soil particles. Horse manure did not significantly improve soil aggregation. A significant correlation (r = 0.955, ρ < 0.01) was found between fungal populations and stable aggregates. No significant correlations were found between stable aggregates in soil and the other parameters assessed. The organic treatments increasing soil microbial populations and promoting their activity appear to be very effecti...

Soil water availability improved by site preparation in a Pinus halepensis afforestation under semiarid climate

This work was funded by the Spanish Comision Interministerial de Ciencia y Tecnologia (CICYT), Projects FOR-91-0352, AGF-95-0097 and AGF-99-1132.

Formation of stable aggregates in degraded soil by amendment with urban refuse and peat

Soil structure has been destroyed over large areas of arid and semi-arid regions by soil degradation processes. This study was conducted to investigate the effects of two organic amendments, urban refuse and peat, on the improvement of soil structure and to analyse correlations between organic carbon content, fungal and bacteria populations and aggregate stability. Two series of five plots were established in the southeast of Spain, in typical Mediterranean semi-arid to arid conditions. To one series different initial doses of urban refuse (0, 6.5, 13, 19.5 and 26 kg m−2) were added, whereas to the other series different doses of peat (0, 10, 20, 30 and 40 kg m−2) were added. The average percentage of stable aggregates showed a significant increase (31.6, 41.1, 53.7, 63.2%) with increased levels of urban refuse with respect to the control. On the other hand, peat was not effective in improving stable aggregates. The beneficial effect which appeared with urban refuse remained in the soil two years after application, probably due to the growth of natural vegetal cover in the treated plots. A marked increase in fungal and bacterial populations and a decrease in extractable organic carbon was observed in the plots into which urban refuse was incorporated. This, together with the high correlation coefficients between the percentage of stable aggregates and the microbial population, suggested that the combined action of polysaccharides from the urban refuse and the increase in microbiological activity was responsible for the initial formation of soil aggregates.

Organic amendment and mycorrhizal inoculation as a practice in afforestation of soils with Pinus halepensis Miller: effect on their microbial activity.

Soil amendment with organic materials prior to afforestation as well as the use of mycorrhizal inoculation, are advisable practices in afforestation of semiarid areas. In this work, the effect of both organic amendment and mycorrhizal treatment on the microbial activity of a soil afforested with Aleppo pine (Pinus halepensis Miller) was studied. Labile carbon fractions (water soluble carbon and water soluble carbohydrates), microbiological parameters (microbial biomass carbon, basal respiration and metabolic quotient), and enzyme activities such as oxydoreductases (deshydrogenase and catalase activities) and hydrolases (urease, protease and phosphatase) were determined. All these parameters were found positively influenced by organic amendment and mycorrhizal treatment of plant roots by inoculation of fungi or forest soil addition. The best result was obtained when mycorrhizal inoculation with fungi was supplemented by organic amendment.

Relations between interrill erosion processes and sediment particle size distribution in a semiarid Mediterranean area of SE of Spain

This research was supported by the EC Environment and Climate Research Programme (Contract no. ENV4-CT97-0687).Abstract Erosion and sediment characteristics were measured using simulated rainfall on two cultivated soils of contrasting lithology (Quaternary calcareous colluvium and Tertiary marls) in a semiarid Mediterranean area of SE Spain. Two rainfall intensities, high (56.0±2.4 mm h −1 ) and medium (31.4±1.4 mm h −1 ), were used in order to know the mechanisms involved in each selected condition. For each simulated event, runoff and sediment were sampled at 1-min intervals on a 1-m wide by 2-m long erosion plot. The erosion rate was calculated as the total amount of soil lost divided by the time period of the test. The duration of the test was that needed to reach steady state runoff, an average time of 24.5 min for Quaternary calcareous colluvium and 17.7 min for Tertiary marls. The size distribution of the transported sediment in the field (effective size distribution) was compared with equivalent measurements of the same samples after chemical and mechanical dispersion (ultimate size distribution) to investigate the detachment and transport mechanisms involved in sediment mobilisation. The results showed that the soil type determined the hydrological response, regardless of the rainfall intensity. The erosional response was, however, determined by the rainfall and soil surface characteristics. In Quaternary calcareous colluvial soils, the predominant erosion process depended on the rainfall intensity, with a prevailing detachment-limited condition in high-intensity events and prevailing transport-limited conditions in those events of medium intensity. These differences in the main erosion processes were reflected in the size of the transported material and in the change in sediment size within the storm. Thus, a time-dependent size distribution of the eroded material (decreasing coarse fractions and increasing fine fractions with runoff time) was observed for high-intensity events. In medium-intensity events, on the other hand, the time-independent size distribution of the eroded material indicated transport-limited erosion. Due to the rapid surface crusting on the Tertiary marl soil, no differences in the main erosion processes or in the sediment size distribution occurred for the different rainfall intensities tested. The erosion of marl soils was determined mainly by the limited quantity of available sediment. The effective size of material was a more sensitive parameter than the ultimate size of the sediment to study the way in which the sediment was transported.

Land rehabilitation by urban refuse amendments in a semi-arid environment: effect on soil chemical properties

Abstract The constituents of urban refuse may have potential chemical benifits in reclaiming degraded soils and improving plant growth, but this may be offset by chemical problems such as increased soil salinity and the accumulation of heavy metals. A series of experiments was conducted in the Fortuna Basin in semi-arid south-east Spain on a Xeric Torriorthent to investigate changes in soil properties with urban refuse amendments varying from 6.5 to 26 kg·m−2. Soil chemical properties were monitored during three years after the application of solid, largely organic, urban refuse. Changes in the contents of potassium, phosphorus, nitrogen, organic carbon, exchangeable sodium, electrical conductivity, and the sodium, chlorine and sulphates in the saturation extract, as well as a number of heavy metals are reported. Salts are quickly leached out, whereas essential plant nutrients are retained. There is a clear medium-term benefit to soil fertility with the use of urban refuse. Potential off-site impacts of diluted toxic contaminants are discussed

Growth response of Pinus halepensis to inoculation with Pisolithus arhizus in a terraced rangeland amended with urban refuse

A field experiment was carried out to evaluate the growth response of Pinus halepensis seedlings inoculated with Pisolithus arhizus and planted in a terraced rangeland amended with urban solid refuse. The application of the organic amendment mediated a significant increase in soil fertility and soil water content. Twenty seven months after planting seedling survival rates did not differ significantly among treatments and were above 95% in all cases. Growth of P. halepensis was significantly (p<0.01) enhanced by the refuse application independently of their mycorrhizal status at the beginning of the experiment. A multiple regression analysis including available soil P concentration and sorptivity as independent variables explained up to 60% of the variance in pine growth observed across treatments. Inoculation with P. arhizus also significantly (p<0.01) enhanced pine growth with repect to the controls grown in both amended and nonamended plots. It was conduded that the combination of soil terracing, refuse amendment and P. arhizus inoculation significantly improved the performance of Pinus halepensis, and this methodology could be successfully applied in afforestation programmes in semiarid and degraded sites.