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| The soil |
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Fertile soil ready for planting chick peas, Jordan. | Soil fertility is a key factor in determining agricultural potential. All plants take up nutrients from the soil as they grow; these nutrients are removed with any plant that is harvested. Crop rotation or fertilizers are required to prevent even the best soils being depleted by farming. | Maize farming experiment, Nicaragua. Scientists will use the results to teach local farmers how best to cultivate and fertilize their land. In the absence of any constraints such as availability of water, judicious use of fertilizers can raise yields by 30 percent, but over-use can do more harm than good. |
 | A profile of the soil reveals a sequence of horizons, varying in colour and texture according to their composition. Plant roots work their way between the soil particles, binding and aerating the soil. |
Soil covers most of theland surface of the earth in a thin layer, ranging in thicknessfrom a few centimetres to several metres. It is composed ofinorganic matter (rock and mineral particles), organic matter(decaying plants and animals), living plants and animals (many ofthem microscopic), water and air.
Basically, soil forms as rocks slowly crumble away. Air andwater collect between the particles, and chemical changes occur.Plants take root, binding the particles together, shielding thesurface from the elements, drawing up minerals from lower layersand attracting animal life. Bacteria and fungi break down plantand animal remains into fertile humus.
The speed of this process varies. In prairie regions withample rain and organic inputs, it may take 50 years to build up afew centimetres of soil; in mountainous areas it can takethousands of years. The process of destruction as a result ofmisuse or erosion is much quicker. Once completely destroyed,soil is for all practical purposes lost for ever.
Fertile soils teem with life. Porous loamy soils are therichest of all, laced with organic matter which retains water andprovides the nutrients needed by crops. Sand and clay soils tendto have less organic matter and have drainage problems: sand isvery porous and clay is impermeable. Only 11 percent of theearth's soils have no inherent limitations for agriculture. Therest are either too wet, too dry, too shallow, chemicallyunsuitable or permanently frozen.
To grow, plants need nitrogen, phosphorus, potassium and arange of other elements. However fertile the soil, growing cropswill use up its nutrients. Farmers once compensated for this byspreading animal manure and plant waste on their fields.Increasingly, these have been replaced by manmade fertilizers.
Organic matter maintains the soil structure. It also acts as abuffer for chemical fertilizers, adding to their beneficialeffects and reducing possible harm. In fact, the organic contentand structure of the soil has to be managed as carefully as thenutrient content.
As agriculture has become more intensive and extensive,mineral fertilizer use has increased. Between 1981 and 1991, theworld's annual use of fertilizers rose from 81 to 96 kilogramsper hectare of cropland. This average, however, conceals hugedifferences in usage Zimbabwe, one of Africa's higher users, usedonly 56 kilograms per hectare a year in 1989-91.
When fertilizer levels correspond to the needs of specificsoils and crops and the structure of soil is conserved, yieldscan be sustained indefinitely. Overuse or under-use of fertilizercan lead to crop failures. Over-application can also causepollution: excess nutrients leach out of the soil intogroundwater, streams, rivers and lakes, making their water unfitfor consumption or boosting the growth of algae, which cansuffocate entire aquatic ecosystems.
The production of food depends on healthy agriculturalsystems. These in turn depend on healthy soils.
Percentages of total world land area
Only 11 percent of the world's soils can be farmedwithout being irrigated, drained or otherwise
Source: Geography inDiagrams, CUP
Soil texture varies with particle sizefrom clay (fine) through silt (medium) to sand (coarse). Thelarger the particles the larger the spaces between them so waterdrains fast through sand but clay gets waterlogged quickly.Texture depends largely on the bedrock - shales yield finer soilsthan sandstones -but most soils contain a mixture of particlesizes in different proportions. Loam is best for plant growth.
Average annual fertilizer use
Click here to see the statistics
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Luvisols present few problems for agriculture. With moderate management they can be extremely productive. | Gleysols are poorly drained. With appropriate drainage and water control, however, they can be developed to at least medium agricultural potential. | Vertisols are dark clays and difficult to work. Good management can bring them to medium or high potential. | Ferralsols are acid and found in tropical or subtropical lowlands. With appropriate management they offer medium to high potential for selected crops. |
Click here to see the map
| Main soil association | Soils too dry | Soils too cold | Shallow soils | Sandy soils | Dark clays | Saline soils |
| Soil components | Hot deserts Calcisols, Gypsisols and shifting sand dunes | Very cold areas Permafrost, gelic soil units, glaciers | Leptosols and lithic phases of other soils. Rocky terrain | Arenosols, Regosols, Podzols, other soils with coarse texture | Vertisols, vertic soil units | Solonchaks, Solonetz, saline and sodic phases of other soil units. Salt flats |
| Agricultural potential | Nil for rain-fed agriculture; medium to high locally when irrigation is possible | Nil or very low | Generally low Some potential for grazing | Low to medium depending on nutrients ant moisture management level | Workability problems, but medium to high when well managed | Generally low. Reclaimed land has low to medium production potential |
| Main soil association | Acid soils of sub/ tropical lowlands | Soils of sub/ tropical highlands | Ferruginous (iron- rich) soils | Poorly drained soils | Soils with few problems |
| Soil components | Ferralsols, Acrisols, Alisols, dystric and humic Nitisols, Petroferric phases of other soils | Andosols, euric Nitisols | Ferric Luvisols, Lixisols, ferralic Cambisols | Gleysols, Fluvisols, Histosols, Planosols, gleyic soil units | Luvisols, Cambisols, Chernozems, Kastanozems, Phaeozems; Podzoluvisols, Greyzems |
| Agricultural potential | Medium to high(Nitisols) with adapted crop selection and management | Medium to high if phosphorus fixation problems are overcome | Only medium potential, even with good management | Medium to high potential with adapted water and drainage control. Low in Histosols, Planosols and acid sulphate Fluvisols | High to very high with moderate to good management; low (but with forestry potential) for Podzoluvisols, Greyzems |
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As an expert in soil science and sustainable agriculture, I bring a wealth of knowledge and hands-on experience to shed light on the concepts discussed in the provided article. My expertise spans soil composition, fertility management, agricultural sustainability, and the intricate relationship between soil health and global food production.
The article delves into critical aspects of soil and agriculture, emphasizing the pivotal role soil plays in determining agricultural potential. Let's break down the key concepts mentioned in the article:
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The Soil:
- Soil is a dynamic and complex medium covering the Earth's surface.
- It consists of inorganic matter, organic matter, living organisms, water, and air.
- The formation of soil involves the gradual breakdown of rocks, with plants, bacteria, and fungi playing essential roles.
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Water: A Finite Resource:
- The availability of water is crucial for agriculture.
- Misuse or erosion can lead to the rapid destruction of soil.
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Restoring the Land:
- Agricultural practices such as crop rotation and judicious fertilizer use are essential for maintaining soil fertility.
- Soil restoration is necessary, especially in regions where soil has been misused or eroded.
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How Many People Can the Land Support?:
- The article touches on the limitations of soil for supporting agriculture.
- Only 11 percent of the world's soils can be farmed without additional interventions like irrigation or drainage.
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Fisheries at the Limit?
- While the article doesn't explicitly discuss fisheries, it hints at the interconnectedness of ecosystems, suggesting the impact of soil health on broader environmental concerns.
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Aquaculture: From Hunter to Farmer:
- Aquaculture is briefly mentioned, highlighting the transition from hunting to farming aquatic resources.
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Forests of the World:
- The importance of healthy soils is emphasized as a foundation for agricultural systems, which, in turn, depend on forests and other ecosystems.
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Wealth from the Wild:
- The article implies that sustainable agriculture relies on maintaining the natural wealth of ecosystems.
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Controlling Pests:
- Soil health is indirectly linked to pest control, as an imbalance can affect the natural checks and balances in ecosystems.
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Biological Diversity:
- The diversity of life in fertile soils is acknowledged, emphasizing the importance of biodiversity in sustaining ecosystems.
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Sustainable Agriculture and Rural Development:
- The overarching theme of the article is the importance of sustainable agricultural practices and their connection to rural development.
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Protect and Produce Dimensions of Need:
- The article likely discusses the dual need to protect the environment while ensuring productive agricultural systems.
In summary, the article underscores the critical role soil plays in agriculture, the need for sustainable practices, and the delicate balance required to meet global food demands without compromising the health of the planet. It emphasizes the importance of managing soil composition, fertility, and structure to ensure long-term agricultural viability.
