Edition 7 of July, 2007

NOTE: This file contains only Sections (5-A) and (5-B) of Chapter 5. The other Section (5-C) is found in another file.

- TABLE OF CONTENTS

(5-A) - Asia - [A1] Central Asia, [A2] Far East, [A3] Asian Sub-Continent, [A4] Southeast Asia, [A5] Middle East,

(5-B) - Africa - [B1] Africa Overall, [B2] North Africa, [B3] Eastern Africa, [B4] Western Africa, [B5] Southern Africa, [B6] Sahel,

(5-D) - South and Central America - [D1] Southeastern South America, [D2] Brazil, [D3] Northwestern South America, [D4]~Central America, [D5] Andean Mountain Region,

(5-E) - Europe and Australia - [E1] Eastern Europe, [E2] Southern Europe, [E3] Northern Europe, [E4] Europe in General, [E5]~European USSR, [E6] Australia,

NOTE: The notation (su1) means that the data is used in the document analyzing the sustainability of the productivity of the world's food, fiber and water supply systems. (See elsewhere in this website.)
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SECTION (5-A) - Erosion and Organic Matter Loss - Asia - [A1] Central Asia, [A2] Far East, [A3] Asian Sub-Continent, [A4]~Southeast Asia, [A5] Middle East,

Asia's land degradation: loss of topsoil (71% of degraded area), terrain deformation (16%); salinity buildup (7%). (China, India, Thailand and Vietnam are the most affected countries.) (96M3).

Kazakhstan, the former Soviet Republic was the site of the Virgin Lands Project launched in the 1950s. To expand grain production, the Soviets plowed an area of virgin grasslands that exceeded the wheat area of Australia and Canada combined. It dramatically boosted production, but by 1980 soil erosion was undermining productivity. During the 24 years since then, half of Kazakhstan's grain land area has been abandoned (04B1).

[A1a] - Erosion and Organic Matter Loss - Central Asia - Armenia -
Erosion in Armenia removes productive soil at 12 million tonnes/ year ((71R1), p.86).

[A1b] - Erosion and Organic Matter Loss - Central Asia - Azerbaidzhan -
Half of total available (agricultural?) land in Azerbaidzhan is eroded and low in productivity (83S2).

26,000 km² (72% of Kazakhstan's wind-eroded cropland) have suffered severe erosion (93M2). Conversion of grazing land to cropland, and removal of straw from fields for use as fodder have severely diminished soil fertility and humus content (4.1% to 2.9% in the past 22 years (a loss of 4500 tonnes/ km²)) (93M2).

In Kazakhstan (largest grain producer in central Asia), the Institute of Soil Management projects a loss of 30% of grain-land because of severe soil erosion (97B3).

In Kazakhstan, over-plowing of marginal land and soil erosion has led to abandonment of 250,000 km² of grain land (03E1). Comments: This might be referring to the former USSR's "Virgin Lands" incursion of croplands into what should have remained grazing lands back in the 1960s - the land area is about the same - see below.

Russia's "Virgin Lands" disaster (late 1950s-early 1960s) is documented in detail on pp. 53-57 of (76E1).

Excess topsoil loss from Soviet croplands is nearly 2.1 Gt./ year (84B2). (85B3), p.19, gives an erosion rate of 2.3 Gt./ year. 5000 km² of Russian croplands are abandoned annually because they are so severely wind-eroded that they are no longer worth farming ((84B3), p. 18) (84B2).

A discussion of Russian agriculture, soils, climate, history, and their inter-relationships is found in (56B1). Soil humus has been lost on almost 25% of Russian land available for agriculture (92F1). Comments: The contention that soil erosion merely moves soil a ways down-wind, and doesn't really destroy croplands seems to be at odds with the Russian data.

The Environmental Ministry reports that half of Russia's arable land is not useable for farming (94H1).

Soil degradation was not widespread before 1860. Degradation was observed on 70% of the Russian Plain during 1860-1917 (91K1).

Increased use of chemical fertilizers and heavy machinery brought increased soil degradation on the Russian Plain since 1917, particularly since 1960. Up to 60% of arable land is affected by erosion in some areas of forest and forest-steppe zone. 25% of Chernozem soils eroded (18% slightly, 5% moderately, 2% severely) (91K1).

Nearly 50% of the 6.1 million km² of cultivated land in the former Soviet Union is imperiled by erosion and other ills. 1.6 million km² are saline, 1.1 million km² are eroded, 0.25 million km² are waterlogged or swampy, 13% more are rocky, hilly or over-grown. Farming has extended into highly marginal rainfall areas, so prospects for expanding the cropland base are not good ((78B2), p. 34).

Pravda reports that the Soviet Union is suffering from a catastrophic decline in soil fertility (90B2). 1000 km² of croplands are lost to gullies yearly. 1.52 million km² (2/3 of arable land) has lost fertility as a result of water- and wind erosion (90B2).

Topsoil erodes away in the former Soviet Union at a rate of at least 1.4 Gt./ year (91F1).

The former Soviet Union abandoned roughly 10,000 km²/ year since 1977, shrinking grain area by 13% (88B4) (89B2).

The greatest degree of erosion is in northern sub-zone of the steppe (Dnepropetrovsk, Donetsk, and Lugansk oblasts; northern parts of Odessa, Nokolayev and Zaporozh'ye oblasts) where 30-54% of the land has been eroded, 10-20% to medium- or heavy degree. Soil loss: 500-2500 m³/ km²/ year (64V1). Comments: 1000-5000 tonnes/ km²/ year)

There is considerable sheet erosion on Turkey's wheat lands (Ref. 34 of (92D1)).

China loses 1200 km²/ year of farm and pasture land to drifting sand dunes (86W2).

Topsoil loss via water and wind in China: 5 Gt./ year (Ref. 17 of (94W3)).

In Shaanxi Province north of Wei River Valley, soil erosion is extremely serious. It affects 130,000 km² (67% of Shaanxi Province). Soil loss estimate: 850 million tonnes/ year. Average erosion rate: 6500 tonnes/ km²/ year in the Loess Plateau of Shaanxi (84L2).

Mizhi County in Yulin Prefecture, China, in middle of Wuding River catchment): Topsoil loss is up to 17,600 tonnes/ km²/ year. (60% of land there has slopes over 35%.) (84L2).

On the southern margin of China's Ordos Plateau, shifting sands in the Mu Us Sandy Land moved over 100 km southward over the past 1000 years. Especially during last 300 years, due to accelerated removal of natural vegetation. A belt of shifting sand 60 km. wide has appeared along the Great Wall (89H4).

Total area of eroded land in China: over 1.5 million km², 15.6% of total land area of 9.6 million km². About 25% of cropland lost half of black earth topsoil after 100 years of cultivation (89H4).

5 billion tons/ year of soil wash to sea from China. Soil erosion affects 1.5 million km². 30% of this occurred after the Revolution (89C3).

Yellow River Basin: 1.6 billion tons/ year of silt moves to Yellow Sea through Yellow River. 40% (720,000 km²) of basin suffers from erosion (89C3).

In China's Sichuan Province, eroded area covers 44%. 20,000 km² of sloped cropland lose 11,000 tonnes/ km²/ year (89C3).

On China's Loess Plateau, the average erosion rate is 5100 tonnes/ km²/ year. Total area: 530,000 km². Population: 70 million. Cultivated area: 133,000 km² (25%). Average erosion rate on cultivated land: 6000 tonnes/ km²/ year. One-third of total soil erosion on Loess Plateau is from cultivated land (93W3).

430,000 km² of China's total Loess Plateau area of 530,000 km² are eroded (84U5). Loess thickness: 30-200 m. "Index of soil erosion" is 2,000-20,000 tonnes/ km²/ year. Areas where water loss and soil erosion occur make up 70-80% of China's Loess Plateau. Soil losses: 2.4-2.5 billion tons/ year. Yellow River carries 1.6 billion tonnes/ year of silt (equivalent to 1 cm over the eroded area of the loess plateau). In Dungzhi Yuan (area 32 km wide x 42 km long, north-south - in Tang Dynasty - 618-907 AD), (cropland?) area believed to have been reduced from 1,344 km² to 756 km² in the last 11 centuries by gully erosion.

The loess plateau in the Huang He's middle reaches is among the most water-eroded areas on Earth. 430,000 km² of deep gullies erode at 5900 tonnes/ km²/ year (89P2). 1.3 million km² of China's land is subject to severe wind- and water erosion. Much dry-farmed cropland lacks sufficient plant cover to protect soil during the wind-erosion season (82B2).

China's loess plateau's wind-deposited soils are 80-100 m. deep. They are 6% sand, 60% silt, 34% clay. They are highly calcareous, with little organic matter (Ref. 2 of (81R1)).

Sediment concentrations in the middle reaches of the Yellow River in China (the loess plateau) approach 700 kg/m³ (about 50% by weight) (81R1). The middle reaches of China's Yellow River are China's most serious source of erosion and sediment. The area is a loess plateau (500,000 km²) of which 110,000 km² produce about 80% of the sediment (81H1). Soil loss in the 4.5 million km² region is 5-112 tons/acre/ year (1100-25,000 tonnes/ km²/ year). On 134,000 km² of farmland, erosion exceeds 30,300 tonnes/ km²/ year (84H1).

China's Yellow River is 5,000 km long; watershed of 680,000 km². Bottom 3-10 m above surrounding plain in North China Plain. River bottom is rising 5-30 cm/ year. Largest sediment load in world (40 kg/ cubic meter). Soil loss in Big Bend loess averages 10,000 tonnes/ km²/ year. (2000-20000 tonnes/ km²/ year). Loess plateau constitutes about 60% of Yellow River watershed. 20% of plateau cultivated. Loess 80-100 m. thick. 6% sand, 60% silt, 34% clay. Highly calcareous. Low in organic matter. 1/3 of plateau is now destroyed or badly damaged by erosion (84H1).

Sediment load of Yellow River is 2800 tonnes/km²/ year over watershed. Gross upstream erosion much higher because of deposition en route to sea. Maximum sediment concentration in middle section of river is 700 kg/ m³, about 50% by weight. Loess sediment becomes plastic when weight exceeds 56%. 50% sediment makes liquid mud (81R2).

Yellow River's bed rises 10 cm/ year in lower reaches (plains). There, the bed 3-8 m above surrounding land. In Henan, the bed is above the level of city walls of Haifeng. The bed is sometimes 12 m above adjoining land (89F1).

An introduction to the history of Indian agriculture is found in (56A1), pp. 324-335. A map of India's erosion rates is in (92S1).

Some Erosion Rate Data for India (92S1)

Siwaliks (India): Estimated soil loss: 16,800 tonnes/ km²/ year (77M1). Comments: This sort of loss is probably purely from cultivated land. It exceeds soil formation rates by a factor of about 15.

Shivalik (Siwalik) Hills located below Himalayas and above Indo-Gangetic Plain in Punjab, Haryana, Himachal Pradesh, and Uttar Pradesh covers over 19000 km². These foothills are sparsely populated and severely eroded (90S5). Severe erosion, frequent landslides, gullies, and flash flooding are attributed to over-grazing and tree-cutting (90S5). Erosion from hilly land in Shivalik (Siwalik) hills is estimated at 10,000-15,000 tonnes/ km²/ year from over 19,000 km² (90S5).

Aravalli Hills divide Rajasthan India into arid (west) and semiarid (east) sections. Over 50% of Rajasthan (350,000 km²) is wasteland due to degradation associated with over-grazing and deforestation (90S6).

India's croplands lose 6 Gt./ year of soil ((84B2), p. 59).

In Himachal Pradesh, Uttar Pradesh, Assain, Jarumu and Kashmir in India, tens of thousands of km² have no more soil covering the rocky substrata (75E1).

In the Deccan black soil region of India, soil erosion rates are 4000-10,000 tonnes/ km²/ year ((86P1), Ref. 5).

India's wastelands - areas affected seriously by salinity, alkalinity, wind- and water erosion - cover one million km², of which 420,000 km² are still being cultivated. Ravines have swallowed 40,000 km² (87U1). (la)

1980 data on degraded land give a total degraded, non-forest land area of 940,000 km² out of India's national land area of 3,290,000 km² (88B1). Water erosion accounts for 74000, wind erosion accounts for 13000, and salinity and alkalinity account for 7000 of the 94,000 km² of degraded land (88B1). (la)

Erosion associated with shifting cultivation has denuded 27,000 km² east of Bihar, India (96G2).

Gullies in India are especially extensive in the Chambral, Yamuna, and Maki River watersheds of north-central and west-central India (Refs. 8 and 15 of (92D1)), and in the state of Bikar (Ref. 49 of (92D1)). Deep gullies occupy even the broad flood plains in Rajasthan, Uttar Pradesh, Madhya Pradesh, Gujarat, and Bihar. These gullies can extend 2-3 km. from river channels in nearly level topography. These gullies form networks that make large sections of flood plain useless (Refs. 13 and 53 of (92D1)). Erosion due to shifting cultivation has denuded 27,000 km² in the states and union territories east of Bihar (Ref. 41 of (92D1)).

In Uttar Pradesh, nearly 55,000 km² are affected by soil erosion: 9000 by wind; 1500 by glacial; 29,400 by sheet/ rill; 15300 by gully-erosion (85P1). Comments: What is "glacial" erosion? (la)

A chapter in (75T1) has maps showing ravined lands in India.

Chandigarh Siwalik Hills between Satluj and Ghaggar Rivers in northwest India cover 302.55 km². These hills suffer from soil loss averaging 367.5 tons/ha/ year due to high rates of development in Chandigarh (02S1). Comments: This is well into the gully erosion range.

Sukhna Lake (Reservoir) in Chandigarh in northwest India experienced siltation right from its completion in 1958. It has a dam 12.8 m high. The lake's initial storage capacity of 1074 ha-m of water. The total catchment area is 40.27 km². The catchment area has rugged terrain, steep slopes, gullies, deep water table and the soils are predominantly alluvial sandy embedded with layers of clay and are highly susceptible to soil erosion. Hill denudation due to deforestation and grazing caused soil erosion (02S1).

In the Annapurna region (central Nepal), erosion on grazing land and croplands is 2000-5000 tonnes/ km²/ year (Ref. 51 of (95D1)).

Bed levels of many Terai rivers in Nepal are rising by 6-12"/ year - causing wider floods and more river meanders that destroy prime farmland ((76E1), p. 80). An Indian study of the silt load threatening a dam- and irrigation project on the Kosi River near the India-Nepal border reported that the Kosi catchment (which includes most of eastern Nepal) was "one of the worst-eroded in the world", and that slopes quickly lose their topsoil and ability to grow crops. Hill slopes are generally cultivated perpendicular to the contour ((76E1), p. 81).

Grain yields per unit area have declined steadily for more than a decade as agriculture has moved onto marginal land, and as soil erosion has worsened ((78B1), p. 51). Ref. (75E1) refers to the Terai region of Nepal (an extension of the Indo-Gangetic Plain of northern India).

Nepal's National Planning Commission reported in 1974 that "Soil erosion is almost to the point of no return. Continuation of present trends may lead to development of a semi-arid type of ecology in hilly regions" (75E1). Nepal may have the (world's) most acute erosion problem, caused primarily by deforestation (92D1).

38% of Nepal's eastern hills consist of fields abandoned due to soil erosion (85J1). Comments: Abandonment of cropland usually reflects gully erosion.

Sheet/ gully erosion affect 36% of Pakistan, notably the rain-fed croplands of the north (Ref.14 of (92D1)).

Soil erosion is a serious threat to 76% of Pakistan's land area (796,000 km² total, 204,000 km² cultivated). Rainfall erosion and gullying affect 36% of the (crop?) land, notably in barani areas. Barani (rain-fed) areas comprise over 25% of cultivated land. Government estimates barani lands lose soil at 1 Gt./ year (89H5). Pakistan (Pothwar Plateau) precipitation = 38-150 cm/ year.

Gullies occupy 60%, which is mantled by a thick cover of loess (90H4). One-third of the area used for agriculture. Barani (rain-fed) lands occupy 25% of 204,000 km² of cultivated land in Pothwar Plateau (90H4). (Note inconsistency with 18,200 km² figure.) Erosion rates: 3800 tonnes/ km²/ year (5-6 mm/ year) (90H4).

Pothwar Plateau (between the Indus- and Jhelum Rivers in Pakistan) is mantled by loess and loess-derived soils. Gullies occupy 60% of Pothwar Plateau, leaving 1/3 suitable for agriculture (89H5).

Gullies occupy 60% of the 18,000 km² Pothwar Plateau, where rain-fed cropping is practiced on uplands between the Indus and Jhelum Rivers (Ref. 14 of (92D1)) (96G2).

[A4] - Erosion and Organic Matter Loss - Southeast Asia - [A4a] Indonesia, [A4b] Java, [A4c] Philippines, [A4d] Tonkin Delta, [A4e]~Thailand, [A4f] Viet Nam,

In contrast to Java's rich volcanic soils, soils of Indonesia's outer islands quickly deteriorate once rain forest is cleared and farmed (Ref. 14 of (88B4)).

There has been a 7-fold increase in silt load in the Citarrum River over a recent 3-year period (76E1) (p. 132). Indonesia's largest reservoir downstream at Jatiluhur is filling rapidly. 13 watersheds in Java have critical erosion problems. "Critical" lands outside of forests cover 5690 km². Soil erosion rates are 990 to 4040 tonnes/ km²/ year and are increasing (90H2).

Indonesia's main island of Java must be one of the most eroded places in Asia, if not the world. Indonesia's government classifies more than 10,000 km² (8% of croplands) as critically eroded (Ref. 56 of (92D1)). The land is said to be so badly degraded that it already is, or soon will be, unable to sustain even subsistence agriculture. Some small fields are losing 5 cm. of soil/ year (150,000 tonnes/ km²/ year) (92D1).

In Java's uplands, the eroded part expands by 1-2%/ year and covers about one third of the cultivated area (96M1).

(Desel River catchment of central Java): Erosion on maize and/or cassava sites: 0.6 mm/ year. Bare soils erodes at 8.2 mm/ year. These data differ from those of other authors by up to 500% (83V1).

Java's Government classifies over 10,000 km² of Java (about 8% of Java's arable area) as "critical" land (so degraded that it is or soon will be unable to sustain even subsistence agriculture). Some fields, practically all small, lose as much as 5 cm. of soil/ year (85U1).

[A4c] - Erosion and Organic Matter Loss - Southeast Asia - Philippines (total land area: 300,000 km²)

170,000 km² of Philippine forestland; 90,000 of 130,000 km² (total) of cropland is eroded. 13 Philippine provinces have over 50% of total area eroded: Batangas (83%), Cebu (76%), Ilocos Sur (73%), La Union (70%), Batanes (68%), Bohol (66%), Masbate (66%), Abra (65%), Iloilo (63%), Cavite (60%), Rizal (56%), Capiz (55%), and Marinduque (51%) (85C5).

58% of Philippine cropland has slope over 11% and is therefore at risk (85C5). (la)

90,000 of 130,000 km² of Philippine croplands are eroded (Ref. 7 of (92D1)). In 13 of the 73 provinces of the Philippines, over 50% of the total area, is eroded (Ref. 38 of (92D1)). As much as one meter of soil has eroded away since WWII, exposing a boulder/ stone substratum (in the Province of Zamboanga del Sur) (92D1). (1 meter/ 46 years = 2 cm/ year) (la)

(Central Luzon region - Pantabangan Dam watershed) 46% of watershed at least severely eroded (75% of A horizon to 25% of B horizon has been removed) (83R1).

In Zamboanga del Sur Province of the Philippines, farmers testify to 80% decline in corn yield over 15 years. Cumulative soil loss has been up to 1 meter. over boulders and core stones (85O2).

Tonkin Delta's 15,000 km² area has 600 people/ km² of cultivated land. All available land in the Tonkin Delta is cultivated, and 50% of the land yields two crops/ year. Population growth rate is high (56G1). An analysis of agriculture of the Tonkin Delta is in (56G1).

1/3 of Thailand is moderately- to severely eroded. Water erosion became a serious problem in the 1950s when forestland increasingly was cleared for cultivation (Ref. 50 of (92D1)). Comments: 1/3 of Thailand in total or 1/3 of agricultural lands?

Thailand (northwest): (precipitation = 95-175 cm/ year). 28% of northwest Thailand is eroded, most of it severely or very severely (90A4). Comments: 28% of all land or 28% of all agricultural land?

Farmed area in northwest Thailand increased 50% during 1980-89 as yields declined (90A4).

Erosion in Thailand (87R1) (All areas in km²)

More than 40% of steep-sloped croplands (62% of Viet Nam) suffer severe erosion (Ref. 26 of (92D1)). Comments: "Steep-sloped" needs a definition.

31% Of Viet Nam's total land area is degraded, including 21% strongly or severely degraded (96M1).

Gullying is severe on, and below, abandoned terraces in Oman (Ref. 57 of (92D1)). Terraced land is being abandoned as people migrate out of rural areas (Ref. 51 of (92D1)).

Gullying is severe on and below abandoned terraces in Yemen (Ref. 57 of (92D1)). Terraced land is abandoned as people migrate out of rural areas (Ref. 51 of (92D1)).

In North Yemen the main problem is destruction of terraces in highlands. (Not enough labor to repair terrace walls.) Rural population has migrated to cities and overseas (89S4).

SECTION (5-B) - Africa - [B1] Africa Overall, [B2] Northern Africa, [B3] Eastern Africa, [B4] Western Africa, [B5] Southern Africa, [B6]~Sahel,

Africa's main type of degradation is loss of topsoil (76% of degraded area) followed by loss of soil nutrients (9%). (Burkina Faso, Burundi, Ethiopia, Madagascar, Lesotho, Morocco and Rwanda are particularly affected.) (96M3).

In Africa, poor land management results in water erosion (46% of soil losses), wind erosion (38%), improper chemical use (12%) and soil compaction due to overgrazing (4%). Good farming practices like allowing land to lie fallow and inter-cropping cereals with legumes and mixed crop/livestock farming - have broken down due to the desperate demand for arable land of a growing population. (10/15/99 ENN Direct)".

Africa's soil loss rate has increased 20-fold during the past 3 decades (80T1). Comments: Is this net rate or gross rate?

Tropical Africa has one of the world's worst soil-erosion problems on arable land (87L1).

The UN-FAO says agricultural production in Africa could drop 25% between 1975-2000 if conservation measures are not adopted (90B2). Comments: The land suffers chemical degradation as well, since fertilizers do not replace mineral losses due to agriculture.

Shifting cultivators of Africa now return to the same plot every 5-10 years instead of waiting 20-30 years as was done earlier (Ref. 8 of (90B2)) (Section (4-C)). Comments: Since it takes 20-30 years for tropical soil to recover from several years of cultivation, the cycle time can be expected to decrease over time, even if population is held constant.

Erosion by wind and water accounts for nearly 86% of total degradation of dryland areas in Sub-Saharan Africa. The remaining 14% is primarily due to the loss of nutrients from excessive cultivation and lack of fertilization (95M1).

About 73% of the total agriculturally used dryland in Africa is affected to some degree by various forms of land degradation (UNEP 1991 data). About 74% of Africa's rangelands, 61% of the rain-fed croplands and 18% of its irrigated lands are affected by desertification at a moderate or higher degree (25+% fertility-loss). In parts of the Sudano-Sahelian region, soil erosion as high as 45,000 tons/ km²/ year are not unusual (97D1). (la)

In sub-Saharan Africa, 72% of arable land and 31% of pastureland is degraded (10/15/99 ENN Direct). (la)

Studies from many African countries show that cropland soil erosion removes far more nutrients than are being added via fertilizer applications (90C1).

0.1-0.4 Gt./ year of wind-borne North African soil are carried out over the Atlantic Ocean ((84B3) p. 16).

Laterized soils occupy 2.5 million km² in West Africa's Savanna (Ref. 46 of (88L1)).

The agricultural outlook for the arid zones of North Africa is grim, owing to the population explosion and the archaic system of production. Rangelands are depleting rapidly, and deserts gain over 1000 km²/ year on average, and soil is lost at 1 mm/ year (1330 tonnes/ km²/ year) by erosion ((70L1), p. 273) ((78B1), p.47).

Deforestation and expansion of cultivation higher up on the sub-humid Tell Atlas Mountains of Algeria have resulted in extensive productivity loss (Ref. 5 of (90D1)).

The coastal range of Morocco and Tunisia is eroding at 3,000 tonnes/ km²/ year. (4 mm./ year). Government stopped terrace building in 1975 (85H3).

Morocco's average soil loss is 3500 tonnes/ km²/ year. Crops are grown on slopes up to 80% (81H3).

In Morocco's Rif region, 50% of lands have slopes over 50%. 60% of retention terraces have been destroyed by gullies and landslides (77B3).

Northwest Tunisia: (Total area: 11,543 km²) Tree-cover in humid regions has been replaced by maquis due to charcoal production and cultivation. Cropped area is expanding up slopes. Mass movement appears to be common on steep slopes. Collecting zones = 24.18%.

Moderate- to severe gully erosion is 33.86% of area affected by sheet erosion (80D1).

Wind erosion in the south, and water erosion in the north, have wrought permanent damage over large areas of Tunisia. Wind erosion damage is greatest in arid grazing lands in the vicinity of Medenine. There, much of the land has a repeating sequence of blowouts between shrubs and hummocks around shrubs. Land productivity probably has been reduced at least 50%, primarily because of the hardness of the subsoil exposed in blowouts (90D1).

Water erosion has severely degraded many soils in the semi-arid and sub-humid western half of Tunisia (Ref. 9 of (90D1)). Sheet erosion has eroded to bedrock in some formerly cultivated land. Gully erosion has devastated much wheat land around El Kef and elsewhere. Evidence of erosion is especially widespread south of the Tell Mountains (90D1).

[B3] - Erosion and Organic Matter Loss - Eastern Africa (Ethiopia, Kenya, Somalia, Sudan, Tanzania) (Note: Eritrea is now part of Ethiopia. It bordered on the Red Sea.) -

In the early 1960s, an American research team and a top-level soil conservation advisor reported: "Even to the casual visitor to Ethiopia, the extent of soil erosion seen in many parts of the country will leave a lasting impression of desolation and impending disaster". In southern Ethiopia's Gamu Highlands, agricultural system was observed to be in a state of collapse around 1968 (Ref. 26 of (75E1)). In northern Ethiopia, "stone deserts" have replaced nearly 40,000 km² of what once was fertile farmland ((88J1), p. 9).

0.9 Gt./ year of topsoil flow from Ethiopia's highlands (area:______) according to a 1978 US AID mission to Addis Ababa ((78B2), p. 25) ((84B2), p. 61) (89B2). "Jagged, intricate and fantastic, Ethiopia's Highlands share with the Himalayas and the Andes, the distinction of being the most erosion-prone areas on earth" (75E1).

In Ethiopia, soil erosion rates as high as 41,000 tonnes/ km²/ year are not unusual (87E2).

Five million acres (20,000 km²) of former, or current, cropland in Ethiopia's highlands have reached the point of no return (Ref. 16 of (90D1)).

Much land in Ethiopia's highlands was eroded to bare rock after less than two decades of cropping ((27) of (90D1)).

40,000 km² of northern Ethiopia have become irreversibly degraded stone desert (90D1).

Reconnaissance soil surveys covering 6000 km² in Ethiopia's Central Plateau region, at elevations of 2000-2800 m. found that all land physically cultivable is now cultivated. The only lands not cultivated are in depressions and on steep rocky slopes (78V1).

USLE indicates erosion of 40,000 tonnes/ km²/ year on Vertisols and 20,000 tonnes/ km²/ year on Cambisols. Most steep slopes are devoid of cover. Gully erosion drains depressions, so cultivation is expanding (78V1). Comments: Erosion rates of 20,000-40,000 tonnes/ km²/ year are strongly indicative of gully erosion - and abandonment.

50% of land area (270,000 km²) of Ethiopia's Highlands is significantly eroded, and 25% (140,000 km²) is seriously eroded. Estimate 20,000 km² of former- or present farmlands have reached "point-of-no-return". Much is now bare rock. Estimate 100,000 km² (18% of highlands) will be bare rock in 2035. By 2010, 38,000 km² of the highlands are predicted to be down to bare rock, and 60,000 km² will be down to a topsoil depth of 10 cm or less (86H2).

Gullies can be seen all over Ethiopia's Highlands (84G2).

In Ethiopia's Wollo Highlands, at present erosion rates, 18% of farmland will be useless for crops by 2010 (87M2).

Ethiopia's Ministry of Agriculture, says Ethiopia's Highlands lose 3 billion tons of soil/ year. Half of farmland (140,000 km²) in Ethiopia's highlands is severely degraded. On 20,000 km², soil lost forever (means "land" lost forever) (87M3). (la)

[B3d] - Erosion and Organic Matter Loss - Eastern Africa -Kenya -
A major, fairly successful national soil conservation program in Kenya is described in ((84B3), p.37-38).

Severe water erosion has permanently damaged much grazing land along the Kenya-Uganda border where the Karamojong, Turkana and Samburu people live (Refs. 1, 33 of (90D1)).

In Kenya's Kiambu and Murang'a districts: row-crop erosion is 1100-5500 tonnes/ km²/ year in both long and short rains (85L1).

In Kenya's central Baringo, estimated soil losses in 2 areas (in the 1930s) were 13,800 tonnes/ km²/ year and 7200 tonnes/ km²/ year (88B6).

In Kenya's Machakos Hills (Total area: 10,000 km²) erosion rates of 5-10 mm/ year are common on poorly conserved, cultivated/ grazed land. USLE erosion on cultivated land (corn): 4900 tonnes/ km²/ year (79M4). Comments: A 1-cm/ year erosion rate implies a topsoil lifetime of a few decades.

A UNESCO study from Sudan reports that the Sahara has expanded southward an average of 90-100 km. during the past 17 years ((78B1), p. 47). Comments: Since then there has been northward movement of the Sahara's southern edge.

Soil erosion rates in Sudan as high as 41,000 tonnes/ km²/ year are not unusual (87E2). Comments: Typical gully erosion rate: 40,000 tonnes/ km²/ year (SECTION (3-H-h)).

In Tanzania's Kondoa Province, nearly 1500 km² are so badly damaged by gully erosion that they cannot be rehabilitated (Ref. 13 of (87E2)). (la)

In Ethiopia and Tanzania, soil erosion rates of 41,000 tonnes/ km²/ year are not unusual (87E2). Comments: Typical gully erosion rate: 40,000 tonnes/ km²/ year (See (3-H-h)).

[B4] - Erosion and Organic Matter Loss - Western Africa (Benin, Cameroon, Cape Verde, Cote D' Ivoire, The Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Nigeria, Sierra Leone) -

Elimination of savanna forest in Ghana raised soil erosion rates from under 100 tonnes/ km²/ year to over 10,000 tonnes km²/ year (90R1). In an area in Ghana's Nangodi State, much land has been stripped of topsoil (Ref. 15 of (90D1)). Nangodi land destruction is said to be representative of northeast Ghana and other parts of West Africa's savanna (90D1).

Ghana's state of Nangodion (along the northeast border): Many areas have been stripped of topsoil. Maximum sustainable population density about 108/ km². Present population density is 386/ km² in parts of Nangodi (72H1).

Nigeria was losing 500 km² of cropland to desertification per year in 2001 (announcement by Nigeria's Minister of Environment, Jan. 2001).

Grain yields/ unit-area have declined steadily for over a decade in Nigeria as agriculture has moved onto marginal lands, causing soil erosion to worsen ((78B1), p. 50). Comments: This could be due to soil nutrient mining - insufficient fertilizer.

Before Nigeria's civil war (late 1960s), geographer Bury Floyd wrote: "The eastern region of Nigeria has some of the most spectacular examples of soil erosion and "badlands" topography in West Africa. Erosion gullies attain a degree of severity and destructiveness seldom experienced in other parts of the continent. Soil deterioration and degradation in terms of progressive loss of nutrients and breakdown of structure is well nigh universal, due largely to over-farming and primitive destructive methods of cultivation ((76E1), p. 142).

A 1974 World Bank study reported that, in Nigeria, fallow periods under shifting cultivation have become too short to restore fertility in some areas. In some locales the original cropping cycle of 10-15 years has been reduced to 5 years ((84B3), p. 13).

Degradation of land and soils among the Tiv people of northeastern Nigeria is described on p. 143-144 of (76E1). The problems apparently were caused by practicing shifting cultivation with too short a fallow period ((76E1), p. 143).

Nigeria shows strong indications of irreversible soil erosion damage on plateaus and escarpments around Enugu in the south, around Jos and Bauchi in the center, and in the vicinity of Zario and Sokoto in the north (Refs.11, 19, 28, 29 of (90D1)).

20-50% of soils in (croplands of) one watershed in northern Nigeria are seriously gullied (77L2).

Gullies have destroyed vast areas in eastern Nigeria (77L2).

Of 78,612 km² in southeastern Nigeria, 70% are affected by sheet and gully erosion. 1,300 km² are affected by gully erosion ((88G1) (Cites Oformata, 1981)). (la)

[B5] - Erosion and Organic Matter Loss - Southern Africa (Angola, Botswana, Lesotho, Madagascar, Mauritius, Mozambique, South Africa, Swaziland, and Zimbabwe (formerly Rhodesia)) -

3-4% of Madagascar is able to support inundated rice fields (Merina and Betsileo lands, with 30-100 people/ km²). The part of Madagascar where ladang (shifting cultivation) must be practiced has no more forest, and supports only scattered, impoverished populations ((56G1), p. 339).

Madagascar is often called the most eroded country in the world. Slash-and-burn rice agriculture on steep forested hillsides ("tavy") is partly to blame - as is cattle raising using procedures that produce large-scale gullying ("lavaka") (89U4).

Natal Province of South Africa (including Kwazulu) loses topsoil at 0.18 Gt./ year (84B2).

Soil loss rate in South Africa is 0.3-0.4 Gt./ year (about 3000 tonnes/ km²) (M.Rampkele, C. McDowell, eds., "Restoring the Land: Environment and Change in South Africa", Panos, London, 1991) Comments: 3000 tonnes/ km² probably refers to croplands. South Africa's total area:?? km²; Cropland area: ?? km².

Striking decline in yields occurred in an area of Lesotho cropland (3640 km²) where population pressure have reduced fallow periods (75W1).

Yield decline in Lesotho during 1950-70 (75W1):
Maize - 57% Sorghum - 22% Wheat - 47% Peas - 60%.
Comments: This could be due to soil nutrient mining - insufficient fertilizer use.

About 150 km² of gullies in the main agricultural regions of Lesotho's plateau (high veld, western Lesotho) alone. Mountain slopes are heavily eroded due to over-grazing (81R3).

The worst soil erosion in Swaziland is in a heavily populated north-south strip in the center of the country (Ref. 23 of (90D1)) where soil productivity loss probably exceeds 20% (of original productivity?) (90D1).

An FAO study concluded that well-managed maize-growing land loses 900 tonnes/ km²/ year; small community farms lose 3600 tonnes/ km²/ year; already-degraded rangeland loses up to 9100 tonnes/ km²/ year in Zimbabwe. The same pattern prevails throughout sub-Saharan Africa (Section (4-H)). A study of 30 countries showed that farmlands in all those countries were losing far more nutrients through erosion than they could afford to apply as fertilizer (90C1). Comments: Fertilizer is far more expensive in Africa than in Europe due to lack of roads and other infrastructure - see elsewhere in this review for details.

An aerial survey of severe soil erosion in Zimbabwe found 18,000 km² severely degraded. 15,300 km² of this is in "Communal Lands", while 2,700 km² of this severe erosion was in lands of large-scale farming enterprises (88W1). Half of African subsistence agricultural land in Zimbabwe could be suffering irreparable erosion damage (Ref. 24 of (90D1)). The degradation problem is aggravated by land tenure policies that concentrate black Africans on marginal land (Ref. 39 of (90D1)).

Topsoil erosion of "communal" (black-owned) lands (42% of Zimbabwe) = 4090 tonnes/ km²/ year (90B3).

Soil survey based on detailed analysis of 8500 aerial photographs, show 18,000 km² of Zimbabwe's land degraded. Figure is conservative because only obvious erosion shows on photos. Most extensive and severe erosion in Communal Lands (peasant farming areas). 15,300 km² affected there. Only 2710 km² of commercial farm land (European-owned farms) are affected (88W2). Comments: Peasant (black) farming areas are on hill-slopes, while commercial farmland is on level plains.

Distribution of Erosion Categories in Zimbabwe (92T2)
15% is very severely eroded.
13% is severely eroded.
19% is moderately eroded.
53% is in relatively good condition (92T2).

Simple model is presented based on estimates of rates of soil loss, existing depths of productive soil, and minimum soil depth required for acceptable crop yields. This model predicts that one area of granitic sand is good for 10 years for maize, and 30 years for sorghum (84E1).

Soil life span 10-20 years under a current loss rate of 6000 tonnes/ km²/ year (35-50 years in communal lands where erosion 5000 tonnes/ km²/ year) (86D2).

Average soil loss: 5400 tonnes/ km²/ year (92T2).

Topsoil loss near Gania in the Inland Delta: as much as 22-31 cm/ year. Average topsoil loss in rice-growing areas of the Inland Delta due to wind erosion: 10 cm/ year (78B5).

[B6b] - Erosion and Organic Matter Loss - Sahel - Sahelian- and Sudanian Zones -
(Burkino Faso, Chad, Gambia, Mali, Mauritania, Niger, Senegal).

82% of rain-fed cropland in Burkino Faso, Chad, Gambia, Mali, Mauritania, Niger, Senegal is at least moderately degraded (89P2). (la)

Average soil erosion in Niger's Majjia Valley = 2000 tonnes/ km²/ year ((88P1), p. 93).