Soil degradation by accelerated erosion is a serious problem and will remain so during the 21st century, especially in developing countries of the tropics and subtropics. Yet, its extent, severity, and economic and environmental impacts are debatable. Estimates of global and regional land area affected are tentative and subjective. Results of field measurements are often technique-dependent. Considerable progress has been made in modeling soil erosion, yet field validation of these models remains to be done for principal soils and ecoregions. Similar to the land area affected, estimates of erosional impacts on crop yield, productivity and soil quality are tentative and subjective. Further, erosion-induced losses on crop yield are scale-dependent because of the compensatory beneficial effects on yields from depositional sites, and technology-dependent because of the masking effects of input such as fertilizers and irrigation. Erosion caused changes in soil carbon dynamics and non-point source water pollution are important environmental impacts. While erosion (e.g., detachment and transport) can lead to emission of trace gases into the atmosphere, deposition can bury and sequester some of the carbon. In addition to improving the database on the land area affected, there is also a need to assess erosional impacts on productivity and soil C balance at the watershed, regional, and global scale. Copyright © 2001 John Wiley & Sons, Ltd.

http://tinread.usarb.md:8888/jspui/bitstream/123456789/1139/1/soil_degradationRA.pdf

Soil degradation by erosion

In this study we analyze the scope and potential impact of reservoir construction on the world's river systems. Water storage behind the global population of large dams represents a 700% increase in the standing stock of natural river water, with residence times for individual impoundments spanning less than one day to several years. The imprint of such storage persists downstream. The mouths of several large rivers show a reservoir-induced aging of continental runoff that exceeds three months. Globally, the mean age of river water has likely tripled to well over one month. From both case studies and global synthesis, we find that this aging can lead to significant changes in net water balance, flow regime, reoxygenation of surface waters, and sediment transport. The pandemic construction of large reservoirs represents an important component of the terrestrial water cycle and one that merits due consideration in future global change studies.

https://www.jstor.org/stable/pdfplus/4314590.pdf

The storage and aging of continental runoff in large reservoir systems of the world

Amazonian dark earths: Origins, properties, management

There is a strong link between desertification of the drylands and emission of CO2 from soil and vegetation to the atmosphere. Thus, there is a strong need to revisit the desertification process so that its reversal can lead to C sequestration and mitigation of the accelerated green- house effect. Drylands of the world occupy 6.31 billion ha (Bha) or 47% of the earth's land area distributed among four climates: hyper-arid (1.0 Bha), arid (1.62 Bha), semi-arid (2.37 Bha) and dry sub-humid (1.32 Bha). Principal soils of drylands are Aridisols (1.66 Bha), Entisols (1.92 Bha), Alfisols (0.38 Bha), Vertisols (0.21 Bha) and others (1.27 Bha). Drylands occur in all continents covering 2.01 Bha in Africa, 2.00 Bha in Asia, 0.68 Bha in Australia, 1.32 Bha in the Americas and 0.30 Bha in Europe. Desertification, degradation of soil and vegetation in drylands resulting from climatic and anthropogenic factors, affects about 1.137 Bha of soils and an additional 2.576 Bha of rangeland vegetation. The rate of desertification is estimated at 5.8 million hectares (Mha) per year. Desertification is a biophysical process (soil, climate and vegetation) driven by socio-economic and political factors. The principal biophysical processes involved, accelerated soil erosion by water and wind and salinization, reduce soil quality and effective rooting depth, decrease vegetal cover, reduce biomass productivity, and accentuate vagaries of climate especially low and variable rainfall. Major consequences of desertification include reduction in the total soil C pool and transfer of C from soil to the atmosphere. Total historic loss of C due to desertification may be 19 to 29 Pg. The rate of C emission from drylands due to accelerated soil erosion is estimated at 0.227 to 0.292 Pg C y −1 . Therefore, desertification control and restoration of degraded soils and ecosystems would improve soil quality, increase the pool of C in soil and biomass, and induce formation of secondary carbonates leading to a reduction of C emissions to the atmosphere. Desertification control and soil restoration are affected by establishing vegetative cover with appropriate species, improving water use efficiency, using supplemental irrigation including water harvesting, developing a strategy of integrated nutrient management for soil fertility enhancement, and adopting improved farming systems. Adoption of these improved practices also have hidden carbon costs, especially those due to production and application of herbicides and nitrogen fertilizers, pumping irrigation water etc. Restoration of eroded and salt-affected soils is important to C sequestration. Total potential of C sequestration in drylands through adoption of these measures is 0.9 to 1.9 Pg C y −1 for a 25- to 50-year period beyond which the rate of sequestration is often too low to be important. In addition to enhancing productivity and food security, C sequestration in soils and ecosystem has numerous ancillary benefits. Therefore, identification and implementation of policies is important to facilitate adoption of recommended practices and for commodification of carbon.

http://tinread.usarb.md:8888/tinread/fulltext/lal/potential_of.pdf

Potential of desertification control to sequester carbon and mitigate the greenhouse effect

Lead, cadmium, arsenic, and zinc were quantified in mine wastes and in soils mixed with mine wastes. Metal concen- trations were found to be heterogeneous in the wastes. Iceberg lettuce, Cherry Belle radishes, Roma bush beans, and Better Boy tomatoes were cultivated in mine wastes and in waste-amended soils. Lettuce and radishes had 100% survival in the 100% mine waste treatments compared to 0% and 25% survival for tomatoes and beans, respectively. Metal concentrations were determined in plant tissues to determine uptake and distribution of metals in the edible plant parts. Individual soil samples were collected beneath each plant to assess metal content in the immediate plant environment. This analysis verified heterogeneous metal content of the mine wastes. The four plant species effectively accumulated and translocated lead, cadmium, arsenic, and zinc. Tomato and bean plants contained the four metals mainly in the roots, and little was translocated to the fruits. Radish roots accumulated less metals compared to the leaves, whereas lettuce roots and leaves accumulated similar concentrations of the four metals. Lettuce leaves and radish roots accumulated significantly more metals than bean and tomato fruits. This accumulation pattern suggests that consumption of lettuce leaves or radish roots from plants grown in mine wastes would pose greater risks to humans and wildlife than would consumption of beans or tomatoes grown in the same area. The potential risk may be mitigated somewhat in humans, as vegetables grown in mine wastes exhibited stunted growth and chlorosis.

Accumulation of heavy metals by vegetables grown in mine wastes.

The Arid Ecosystem Elements of the Climate Classification of the Earth to Climatic Regions Natural Vegetative Cover in Arid Ecosystems Soils of the Arid Ecosystems References Salt-Affected Soils Introduction The Size of the Problem Characteristics of Salt-Affected Soils Studies Required for Predicting Salinization Due to Upward Movement of Groundwater and its Subsequent Evaporation Effect of Salinity on Plant Growth and Composition References Calcareous Soils Introduction Morphology Physical Properties Chemical and Fertility Properties Gypsic Soils Management of Calcareous Soils References Sandy Soils Introduction Formation of Sandy Soils The Sandy Soils in Soil Classification Systems Physical Characteristics Management of Sandy Soils References Water Management in Arid Ecosystems Introduction Technologies for Increasing Water Resources Management of Rain-Fed Agriculture Irrigation Drainage Use of Low-Quality Water for Irrigation References Desertification Introduction Soil Degradation Degradation Versus Desertification Desertification Due to Sand Movement Desertification of Rangeland Desertification Due to Irrigation and Waterlogging Combating Desertification in Rain-Fed Croplands Complementary Measures for Combating Desertification Soil Erosion Water Erosion Wind Erosion Desertification, a Global Challenge References Index

Management of problem soils in arid ecosystems

One seedling of tomato was planted in each pot containing 3 1.c. of either clay, CaCO3-rich, sandy soils or washed sand. Increments of Pb(NO3)2 were added to the soil or sprayed on the plants of the washed sand pots. Burning of leaves' margins were noticed on the sprayed plants. The fruits' fresh and dry weights significantly decreased with Pb increments and exponential equations were used to express this relationship. Comparing the slopes of the equations indicated that the Pb effect on yield of plants grown on clay: CaCO3-rich sandy soils is equivalent to 1:0.63:0.66, respectively. The correlation coefficients between Pb concentration in the shoots and the weight of tomato fruits were −0.869, −0.944, −0.911 and −0.845 for the plants grown on the three soils and washed sand, respectively. Straight line equations were established to express the relation between Pb concentration in the shoots and in the fruits.

Effect of lead increments on the yield and lead content of tomato plants

The composition of Nile River water was examined to show the effect of the Asswan High Dam on the fertility and salinity of the water for irrigation. The Nile water contains about 110 x 10/sup 6/ metric tons/year of suspended materials as it crosses the Egyptian border. Before the Asswan High Dam was constructed, 24 x 10/sup 6/ metric tons/year of solids were deposited, mainly on the Egyptian flood plains. After the dam was finished, only 2.1 x 10/sup 6/ metric tons/year of solids were present in the Nile water to be deposited on the Egyptian soils; the remainder, 21.9 x 10/sup 6/ metric tons/year of solids, settled out in Lake Nasser. The loss of nutrients in the sediments which settled out in Lake Nasser, and the gain in soluble cations which resulted from construction of the Dam, were calculated from sediments and water analyses. The loss of 12,000 metric tons/year of sediment N is probably not significant for Egyptian agriculture. The loss of P, including a maximum of 6000 metric tons/year of soluble P, will probably require a significant increase in the use of P fertilizers. The quality of the Nile water for irrigation, as determined by values formore » electrical conductivity, sodium adsorption ratio, adjusted sodium adsorption ratio, residual carbonate, and pHc, did not change significantly after construction of the dam.« less

Evaluation of Changes in the Nile Water Composition Resulting from The Asswan High Dam

Polynomial quadratic equations were established to express effects of zero, one, and two plowings on the efficiencies and contributions of soil nitrogen (Ns) and 0, 1, 2, 3, 4, and 5 units of fertilizer nitrogen (NF) to wheat grain yield. Ns was evaluated by: (a) K2SO4 extraction and found 1.7, 1.9, and 2.0 units of M (I unit = 100 kg N ha‐1) at TO, T1, and T2, respectively; (b) B0/exs‐the intercept divided by the efficiency of soil nutrient‐and found 1.31, 1.48, 1.70, 1.99, and 2.4 units at each NF rate of application from zero to four, respectively, and increased with tillage treatment; and (c) solving the polynomial equation for X when Y = 0 and found 1.10, 1.32, and 1.42 units of NF at To, T1, and T2, respectively. The efficiency of applied NF, (ex.) along the range of its application was found as ex = B1 + B2Xi and decreased with an NF rate from 2.44 at NF1 to 1.51 Mg unit‐1 ha‐1 at NFi at To and from 2.55 and 2.62 at T1 and T2 to 1.50 and 1.51 Mg unit‐1ha‐1 respectively. The efficiencies of soil N w...

A. Monem Balba

Papers

Management of problem soils in arid ecosystems

Effect of lead increments on the yield and lead content of tomato plants

Evaluation of Changes in the Nile Water Composition Resulting from The Asswan High Dam

Soil and fertilizer‐N efficiencies using wheat grain response equations to N and tillage

New Fields for the Application of the Mitscherlich Equation