Nature And Properties Of Soils

This is a review of worldwide land degradation problems. Four themes are emphasized: delineating and estimating the magnitude of soil erosion, quantifying erosion and sedimentation impacts on land productivity, establishing quantitative values for erosion-causing parameters, and implementing global and regional soil and water conservation programs. Papers deal with both developing and developed countries and illustrate how erosion control techniques used in developed countries can or cannot be applied in developing countries.

https://gendocs.ru/docs/29/28948/conv_1/file1.pdf

Soil Erosion and Conservation

Assessing the impacts of climatic and, in particular, land use changes on rates of soil erosion by water is the objective of many national and international research projects. However, over the last decades, most research dealing with soil erosion by water has concentrated on sheet (interrill) and rill erosion processes operating at the (runoff) plot scale. Relatively few studies have been conducted on gully erosion operating at larger spatial scales. Recent studies indicate that (1) gully erosion represents an important sediment source in a range of environments and (2) gullies are effective links for transferring runoff and sediment from uplands to valley bottoms and permanent channels where they aggravate off site effects of water erosion. In other words, once gullies develop, they increase the connectivity in the landscape. Many cases of damage (sediment and chemical) to watercourses and properties by runoff from agricultural land relate to (ephemeral) gullying. Consequently, there is a need for monitoring, experimental and modelling studies of gully erosion as a basis for predicting the effects of environmental change (climatic and land use changes) on gully erosion rates. In this respect, various research questions can be identified. The most important ones are: (1) What is the contribution of gully erosion to overall soil loss and sediment production at various temporal and spatial scales and under different climatic and land use conditions? (2) What are appropriate measuring techniques for monitoring and experimental studies of the initiation and development of various gully types at various temporal and spatial scales? (3) Can we identify critical thresholds for the initiation, development and infilling of gullies in different environments in terms of flow hydraulics, rain, topography, soils and land use? (4) How does gully erosion interact with hydrological processes as well as with other soil degradation processes? (5) What are appropriate models of gully erosion, capable of predicting (a) erosion rates at various temporal and spatial scales and (b) the impact of gully development on hydrology, sediment yield and landscape evolution? (6) What are efficient gully prevention and gully control measures? What can be learned from failures and successes of gully erosion control programmes? These questions need to be answered first if we want to improve our insights into the impacts of environmental change on gully erosion. This paper highlights some of these issues by reviewing recent examples taken from various environments.

Gully erosion and environmental change: importance and research needs

The Analysis of Variance.

Sampling and analysis or visual examination of soil to assess its status and use potential is widely practiced from plot to national scales. However, the choice of relevant soil attributes and interpretation of measurements are not straightforward, because of the complexity and site-specificity of soils, legacy effects of previous land use, and trade-offs between ecosystem services. Here we review soil quality and related concepts, in terms of definition, assessment approaches, and indicator selection and interpretation. We identify the most frequently used soil quality indicators under agricultural land use. We find that explicit evaluation of soil quality with respect to specific soil threats, soil functions and ecosystem services has rarely been implemented, and few approaches provide clear interpretation schemes of measured indicator values. This limits their adoption by land managers as well as policy. We also consider novel indicators that address currently neglected though important soil properties and processes, and we list the crucial steps in the development of a soil quality assessment procedure that is scientifically sound and supports management and policy decisions that account for the multi-functionality of soil. This requires the involvement of the pertinent actors, stakeholders and end-users to a much larger degree than practiced to date.

Soil quality – A critical review

Estimation of long term soil loss using copper as a tracer.

Soil erosion by water is a severe problem in the eastern loess belt of Northern China, particularly on agricultural land. The erosion problems are to a large extent associated with improper soil tillage practices. Changing the current tillage practices could therefore reduce soil loss. This will, however, also affect the water balance and hence the available water for crop growth, particularly in dryland farming systems. A field study was carried out on five plots on a slope field near Luoyang, Henan province, China, in order to compare the water balance under different soil tillage practices. The terms of the water balance were determined from August 1999 until April 2001. From October to June all plots were under winter wheat. After harvesting, four soil tillage practices were applied: conventional tillage, no tillage, subsoiling and reduced tillage. A two-crop rotation of winter wheat and summer corn or peanuts was applied as well. Analysis of the different components of the soil water balance enabled to determine the most suitable practice for crop growth. The results, though preliminary at this stage of the study, show that subsoiling resulted in the highest increase in moisture storage and lowest evaporation during the fallow period. The two-crop rotation with peanuts also showed promising results, mainly due to decreased evaporation of the soil surface. The no-tillage and conventional tillage gave intermediate results, whereas the reduced tillage was the worst alternative. Keyworks: dryland, loess soil, slope land, conservation tillage, water balance

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The Water Balance as Affected by Conservation and Conventional Tillage Practices on Slope Fields in the Drylands of North China

Monotemporal assessment of the population structure of Acacia tortilis (Forssk.) Hayne ssp. raddiana (Savi) Brenan in Bou Hedma National Park, Tunisia: A terrestrial and remote sensing approach

To gain additional knowledge and better understand forest soil management on a small scale, geostatistical analytical tools were employed to examine the spatial distribution in dry aggregate mean weight diameter (MWD) and other selected soil properties and to assess the possible relationships between MWD and other soil properties. Selected properties of forest soils collected along a 300-m transact in the Nimbia Forest Reserve of Nigeria exhibited moderate to high variability in distribution with sodium ion displaying the greatest variability [coefficient of variation (CV, 91.2%)] and principal component analysis revealed the exchange complex cluster as influencing total variation of field soil properties. The autocorrelation function showed significant spatial correlation from 1 lag in soil organic carbon up to 17 lags (51 m) in soil moisture content (θ). The spherical and Gaussian semivariogram models described the spatial structure of most soil properties; however, for clay, cation exchange capacity (C...

Assessment of Spatial Distribution of Selected Soil Properties using Geospatial Statistical Tools

Recent studies of soil loss by the integrated action of raindrop impact and wind transport have demonstrated the significance of this mechanism. This paper presents data obtained during wind-tunnel experiments examining the ‘Raindrop Detachment and Wind-driven Transport’ (RD-WDT) process to investigate average sand particle trajectory and the spatial extent at which the process operates. In the experimental design, at the same time as the horizontal wind velocities of 6·4, 10, and 12 m s–1 passed through the tunnel, rainfall was simulated falling on very well sorted dune sand. The aspect and slope of the sand bed was varied to reproduce both windward (Ww) and leeward (Lw) slopes of 4o and 9o with respect to the prevailing wind direction. The average sand particle trajectories by the RD-WDT process () were estimated by a mass-distribution function, which was integrated over a 7-m uniform slope segment. The results showed that depended statistically upon the wind shear velocity (u*), and the effect of the slope gradient (θ) was insignificant on . This was different from that of the windless rain process (), ‘Raindrop Detachment and Splash-driven Transport’ (RD-ST), the spatial range of which relies strongly on θ. Additionally, was approximately 2·27 ± 2·2 times greater than the average path of a typical saltating sand particle of the rainless wind (), ‘Wind Erosion Saltation Transport’ (WE-ST). Copyright © 2009 John Wiley & Sons, Ltd.

Donald Gabriëls

Papers

Estimation of long term soil loss using copper as a tracer.

The Water Balance as Affected by Conservation and Conventional Tillage Practices on Slope Fields in the Drylands of North China

Monotemporal assessment of the population structure of Acacia tortilis (Forssk.) Hayne ssp. raddiana (Savi) Brenan in Bou Hedma National Park, Tunisia: A terrestrial and remote sensing approach

Assessment of Spatial Distribution of Selected Soil Properties using Geospatial Statistical Tools

Average sand particle trajectory examined by the Raindrop Detachment and Wind‐driven Transport (RD‐WDT) process