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Agriculture defines and sustains our modern lives, but it often leads to ecosystem destruction.These factors are especially critical for plants, animals, soil systems, and water resources.As human efforts are made to sustain and improve human well-being, understanding, evaluating, and balancing agricultural disturbances of soil and water resources is crucial.The knowledge discussed here influences our emerging ethical and responsible approach to human populations and ecosystems in the future.

The evolution of modern humans has been largely based on small, mobile, kin-based social groups, such as bands and tribes, even as agriculture is essential to human food and stability (Diamond 1999, Johanson & Edgar 2006).The majority of our food was derived from wild plant and animal sources before we began relying on agriculture and soil management.The Agricultural Revolution has accelerated our social evolution and been facilitated by our dependence on domesticated plants and animals grown in highly managed soils and water systems as we have grown.

An anthropogenic influence on the environment was first seen through the early use of fire as a method of flushing out wildlife and clearing forest land. .In addition to these and other factors (such as population pressures, climate changes, and encouraging/protecting desirable plants), these helped lay the foundation for the Agricultural Revolution and changed the relationship between humans and the earth forever.As hunter-gatherer societies became agrarian, the course of human history radically changed and natural nutrient cycles within soils irreversibly changed.In the dawn of the Neolithic Period, humans planted the first crop seeds in the soil, which provided the necessary nutrients for plants and served as the foundation for human agriculture.


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It is generally accepted that 17 elements are required for a healthy plant (Troeh & Thompson 1993).Table 1 shows how a lack of any one of the essential nutrients listed there may severely limit crop yields - an example of the principle of limiting factors.Among the mineral elements, the primary macronutrients (N, P, and K) are needed in the greatest quantity and are the ones that may be in short supply in agricultural soils.Typically, secondary macronutrients are present in sufficient amounts in soil and, therefore, do not often limit crop growth.In miniature amounts, micronutrients, or sometimes called trace nutrients, are crucial to plants, but if too much is consumed, they can be toxic.The ubiquitous presence of silicon (Si) and sodium (Na) in soils means that neither are ever in short supply (Epstein 1994, Subbarao et al. 2003).

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The natural cycle of nutrients in soil is altered by agriculture.Plant nutrients can be effectively mined from the soil when crops are intensively cultivated and harvested.In order to maintain sufficient crop yields, soil amendments are typically needed.During the early days of mankind, humans used animal manure, charcoal, ash and lime (CaCO3) to improve soil fertility.Farmer addition of numerous soil amendments increases soil fertility today, including chemical fertilizers and organic sources of nutrients, such as manure or compost, which often result in an excess of primary macronutrients.A fertiliser application or use by crops is often not optimized, and excess nutrient, especially N and P, can be carried by surface runoff or leach from agricultural fields and pollute surface- and groundwater (Moss 2008, Sharpley et al. 2002).


While soil is often described as a "fertile substrate," not all soils are suitable for growing crops.Mineral components contribute to the ideal soil composition (sand 0.05–2 mm, silt 0.002–0.05 mm, clay 0.002–0.05 mm, inorganic soil components clay: inorganic soil components)

Soil Organic Matter (SOM)