Formation, Fertility and Loss

1. Soil Formation, Fertility and Loss

2. Soil Formation There are several factors that interact to bring about soil formation. These include:

3. 1. Soil Formation: weathering Weathering: The break down of rock, which does not involve transport. Weathering creates the mineral particles that will form the soil. There are several different types: • Chemical weathering • Physical weathering • Biological weathering

4. 2. Soil Formation, humification Humification: the formation of humus from dead organic matter by decomposers and saprobionts. Humus contributes to the soil in several ways: • It sticks together the mineral particles together reducing erosion. • It holds water. • As part of the cation exchange complex (along with clay) it improves the soils ability to hold water

5. 3. Soil Formation, organic sorting Organic sorting: Living organisms such as earthworms literally eat the soil particles and leaf litter. As a consequence this turns over the soil in effect ploughing it.

6. 4. Soil Formation, chelation leaf litter leaf litter Chelation: Living organisms create organic compounds which release acids.Water passing through the leaf litter on the top of the soil carries these acids through the soil which breaks down and mobilise mineral particles and organic matter. Some types of vegetation eg. Pine needles release more organic acids than others and thus create more chelation. Soils under coniferous trees such as pine tend to be acid as a consequence.

7. 5. Soil Formation, translocation Translocation: the movement of material in solution or suspension from one soil horizon to another.

8. Eluviation The process by which the mineral particles and nutrients are leached out of the upper layers of the soil. 5. Soil Formation, eluviation and illuviation Soil surface Illuviation The process by which the mineral particles and nutrients are washed into the lower layers of the soil. Water table

9. 5. Soil Formation, aggregation Aggregation: When soil particles cluster and stick together to form a single unit such as a crumb ped.

10. 6. Soil Formation, time Time: Soils develop over long periods of time. In sand dune as succession proceeds the organic content of the soil increases and, as it does so, the water retention increases and there are changes in pH, nutrient content and the diversity of living organisms. The rate of soil loss in many parts of the world greatly exceeds the rate of formation

11. Organisms Topography Soil Parent Material Climate Soil Formation Weathering Precipitation, temperature, etc Leaching, hydrolysis, Rate of formation etc. Depth of soil, drainage and runoff. Microclimatic effects of vegetation cover Weathering Resistance to weathering Available mineral nutrients and water Humidity, temperature, light Chemical composition and particle size Amount and type of humus, soil, mixing and aeration

12. Soil Fertility

13. Soil Fertility High Fertility Low Fertility Component Clay soils will be be harder for plant roots to penetrate and be more poorly aerated. Sandy soils although well aerated lack the ability to retain nutrients and water A soil with a mixture of about 1/3 clay, 1/3 silt and 1/3 sand, (Loam), will give the right balance of drainage, nutrient retention, aeration etc. Texture A function of texture, structure, depth, aeration, pH, moisture and nutrient content A crumb ped gives the best arrangement of particles and DOM to allow water/nutrient retention, aeration etc. Blocky and platy peds are harder for plant roots to penetrate Structure A soil may be shallow for a variety of reasons e.g. angle of slope, age erosion, etc. Shallow soils are less capable of anchoring plants and tend to have fewer nutrients, water A deep soil will inevitably have a greater capacity for anchoring plants and supplying them with the water and nutrients they require. Depth

14. Soil Fertility High Fertility Low Fertility Component Waterlogged soils tend to lack oxygen. As a consequence there is less decomposition of DOM by decomposers and saprobionts. Nitrates undergo denitrification to nitrogen gas. A fertile contains air. Which provides oxygen for aerobic respiration by plant roots, decomposers, saprobionts and nitrifying bacteria Aeration In Soils with extremes of pH some nutrients become less available. Acid soil leaching of minerals and nutrients occurs. A soil with a pH 6-7, (neutral) nutrients are accessible to plant roots pH Too little water will limit plant growth partly by limiting nutrient avalability. Too much water will reduce aeration and may cause leaching. Moisture Plants require water for growth.

15. Soil Fertility High Fertility Low Fertility Component Plants require nutrients such as nitrates , phosphates and potassium (N, P and K). Nutrient retention will be affected by texture, ped, aeration, water content, pH etc, Humans may modify these factors to improve retention. Humans may add nutrients by using inorganic/organic fertilizers or by rotating with legumes such as clover Without nutrients plant growth will be stunted. There are several possible reasons low nutrient levels. Poor texture e.g. sandy soils, Poor structure, translocation of minerals/nutrients, waterlogged soil, extremes of pH, harvesting of crops which removes nutrients from a field. Nutrients

16. Soil Fertility, pH 6.5 pH: The pH of soil effects the availability of plant nutrients and thus soil fertility. A pH of 6.5-7.0 is optimum for the majority of nutrients. Farmers adjust the pH of the soil by adding lime to raise the pH of acid soils and thereby increasing the availability of nutrients such as phosphorus and potassium.

17. Soil Loss

18. Soil Loss Why are soils important? What are the many causes of soil loss?

19. Soil Loss, erosion Erosion: those processes which wear away the surface of the land

20. Soil Loss Soil erosion can be divided into three types: i. Sheet erosion: the removal of surface material by water flowing over the surface usually on low gradient slopes ii. Rill: The removal of surface material by running water down a gradient with the formation of small channels, rills. iii. Gully: The formation of large deep channels from smaller ones (rills) by the rapid movement of water down a gradient. Produces severe soil erosion

21. Soil Loss There are several possible causes of soil erosion 1.Rain splash 2.Surface runoff 3.Wind blow 4. Deforestation 5. Overgrazing 6. Reduced dead organic matter 7. Soil exhaustion 8. Ploughing of vulnerable soils

22. Soil Lossrain splash Rain Slope Rain Splash: On a slope the impact of raindrops causes soil particles to be carried down the slope. Movement of soil down slope Soil accumulating at the bottom of the slope

23. Soil Losssurfacerun off Rain Rain Slope Surface runoff: The water flowing over the land surface will carry soil particles with it which will then accumulate at the bottom of the slope. Surface runoff Movement of soil down slope Soil accumulating at the bottom of the slope

24. Soil Loss, windblow Windblow: Soils exposed to the wind may be picked up and carried long distances. The greater the windspeed the larger the particle that can be moved.

25. Soil Loss, exhaustion Exhaustion: Harvesting of crops removes nutrients and organic matter from the soil. As a consequence the soil may lose its structure and this will increase the rate of erosion. The loss of nutrients will reduce the crop yield.

26. Soil Loss, deforestation Deforestation: The removal of the tree cover leads to less interception and more surface run off. The consequent greater speed and amount of water flowing over the surface increases the rate of erosion.

27. Soil Loss, overgrazing Overgrazing: The consequences of overgrazing are impaction of the ground and removal of covering vegetation. The results are increased surface runoff and increased soil erosion.

28. Soil Loss, reduced DOM Reduced DOM: Dead organic matter binds the soil particles together, contributes to the soil ped and helps retain soil nutrients. Harvesting reduces the amount of DOM entering the soil. Fertilisers speed up the decomposition of the DOM. The consequence is the soil gradually losses its structure and erosion will increase.

29. Soil Loss, ploughing of vulnerable soils Ploughing: ploughing removes plant cover which is largely responsible for holding the soil in place. Shallow soils on slopes, particularly those with a sandy texture are likely to erode easily after ploughing. Contour ploughing reduces the movement of the soil down down the slope.

30. Soil Loss, sediment traps To measure the amount of soil erosion sediment traps can be equally placed down a slope and the amount of soil carried down the slope by surface run off can be measured. By weighing the sediment trapped at regular intervals

31. Soil and Civilization 3500 BC: Wheat and barley are nearly equal in occurrence in southern Iraq. 2500 BC: The less-salt-tolerant wheat accounts for 1/6 of the crop. 2300 BC: Wheat is no longer grown in the Sumarian city-state of Agode 2200 BC: Wheat accounts for 2% of the crop in Girsu. 2100 BC: The city of Ur abandons wheat production. Wheat now just 2% of the crop in the Sumerian region. 2000 BC: Isin and Larsa no longer grow wheat. 1700 BC: Wheat abandoned completely in the south. The Fertile Crescent 1 In the Western world agriculture began in an area of land called the fertile crescent at the western end of the Mediterranean about 7000 to 6000 years ago. This led to the development of settled civilizations such as the the Sumerians who developed the first writing cuneiform. Poor agricultural techniques led to deforestation, salination and erosion. Without food to support their populations these civilizations collapsed.

32. Soil and Civilization The Fertile Crescent 2 Crop yields were recorded in cuneiform tablets in the region of Girsu: 2400 BC: yields 253.7 m3/ km2 2100 BC: yields 146. m3/ km2 1700 BC: yields 89.7 m3/ km2 Deforestation and over-grazing in the eastern Turkey led to widespread erosion and is thought that this is the source of the silt load which destroyed and the irrigation system on which the population depended. This is believed to be the root cause of the decline of the Mesopotamian civilization. Between 700 BC and the 20th century AD the coastline at the mouth of the Tigris and Euphrates Rivers changes due to siltation. The Persian Gulf is shortened by 150 miles by the silt load of these rivers. A Cuneiform Tablet

33. Soil and Civilization Rome and North Africa In Roman times as many as 15,000,000 bushels of grain were transported annually from North Africa and Egypt to Rome, where now their is only desert. North Africa had a large, prosperous agriculture during 200 BC-600 AD, as much evidence shows. Erosion largely caused by deforestation is thought to be the reason for the decline. The land was probably already more-or-less ruined by erosion when Arabs conquered the area near the end of the 7th century AD. By the 10th century the situation was said to have become even worse. No more than 10% of the original forests that once stretched from Morocco to Afghanistan as late as 2000 BC still exist . A Roman African

34. Soil and Civilization Easter Island Easter Island, off the coast of Chile has, fertile volcanic soils. Archaeological finds and ancient pollen show that when Polynesians arrived on Easter Island, it was covered with a lush subtropical forest of palm trees and giant sunflowers, inhabited by land birds and breeding sea birds. Easter Island sustained a population of 58 people/ km2. But the population stripped the forests bare and killed the native animals. By 1500, all that was left was grassland. "People turned to the largest protein source around-cannibalism. Easter Island society collapsed in an epidemic of warfare. When the first Europeans reached the island in 1722, two-thirds of its population had died. 1550: Population of Easter Island 7000. 1722: Population of Easter Island 2333 1850: Population after deforestation and collapse of natural and agricultural systems: 100

35. Soil and Civilization The Dust Bowl Poor agricultural practices and years of sustained drought caused the Dust Bowl. Plains grasslands had been deeply ploughed and planted to wheat. During the years when there was adequate rainfall, the land produced bountiful crops. But as the droughts of the early 1930s deepened, the farmers kept ploughing and planting and nothing would grow. The ground cover that held the soil in place was gone. The Plains winds whipped across the fields raising billowing clouds of dust to the skies. The skies could darken for days, and even the most well sealed homes could have a thick layer of dust on furniture. In some places the dust would drift like snow, covering farmsteads

36. Soil and Civilization The Grapes of Wrath:John Steinbeck wrote in his 1939 novel "And then the dispossessed were drawn west- from Kansas, Oklahoma, Texas, New Mexico; from Nevada and Arkansas, families, tribes, dusted out, tractored out. Car-loads, caravans, homeless and hungry; twenty thousand and fifty thousand and a hundred thousand and two hundred thousand. They streamed over the mountains, hungry and restless - restless as ants, scurrying to find work to do - to lift, to push, to pull, to pick, to cut - anything, any burden to bear, for food. The kids are hungry. We got no place to live. Like ants scurrying for work, for food, and most of all for land."

37. Soil and Civilization Scientists say impoverishment of the soil is a major threat to the Earth's ability to feed itself. They have found that nearly 40% of the world's agricultural land is seriously degraded. The damage has already had "a significant impact" on the productivity of about 16% of the planet's farmland. The economic and social effects are currently having a greater impact in developing countries than in rich ones. However loss of soil is still significant in developed countries. In California it is estimated that it takes 2000 years for one inch of topsoil to be created. Currently one inch is being lost every 25 years. It is being lost 80 times faster than it is made .

38. Ozymandias I met a traveler from an antique landWho said: Two vast and trunkless legs of stoneStand in the desert. Near them, on the sand,Half sunk, a shattered visage lies, whose frown,And wrinkled lip, and sneer of cold command,Tell that its sculptor well those passions read,Which yet survive, stamped on these lifeless things,The hand that mocked them, and the heart that fed,And on the pedestal these words appear:"My name is Ozymandias, King of Kings:Look upon my works, ye Mighty, and despair!"Nothing beside remains. Round the decayOf that colossal wreck, boundless and bareThe lone and level sands stretch far away. -Percy Bysshe Shelley1792-1822