Mason1_1 - Soils Introduction The thin layer of soil at the...

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Soils Introduction The thin layer of soil at the earth's surface is essential for maintaining life. This layer of soil is the basis of most agriculture around the globe. If soil is lost or degraded, the potential of an area to support both plant and animal life is greatly reduced. Whilst the actual definition of sustainable farming varies somewhat, conservation and rejuvenation of agricultural soils are essential elements of any sustainable agricultural system. It is important to understand that soil is not the property of the land owner, the lease holder or the tenant of the site. It is the property of everyone, now and in the future. It may take many thousands of years for a soil to form, but only a few years for it to be degraded or lost due to poor management practices. For this reason it is critical that the techniques we use to manage our soils will maintain them in a manner that ensures that they are at least as productive for future generations as they are now, and hopefully are even improved. Growing media The growing medium is the material (or space) in which plant roots grow. This has tradi- tionally been soil, but with the application of modern technology, we are provided with other options for growing media. There are three main options: 1. Sustained Organic Soils. In nature, the best soils contain at least 510% organic matter. Organic matter influences soil and water systems which in turn modify organic matter turnover and nutrient cycling. Maintaining the levels of organic matter in soils is a vital element of sustainable agricultural production. 2. Technologically Supported Soils. By adding fertilisers and soil ameliorants (eg lime) and by irrigating heavily, technology enables us to grow almost anything in almost any soil. Unfortunately, this is an inefficient use of resources and can result in serious degradation of soils, as well creating further problems, such as excess nutrients entering our waterways and causing problems such as algal blooms.
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24 1 Sustainable Agriculture 3. Hydroponics. Despite being an 'artificial' way of growing plants, hydroponics can be sustainable if it is well managed and relatively environmentally friendly. It allows you to take full control over the root zone: excess nutrients are not 'lost' and washed into surrounding areas chemical residues can be collected, treated and disposed of properly water loss can be minimised, and water use maximised Of the three options above, the least sustainable is the most commonly practised (ie technologically supported soils). This is probably because it is the easiest approach in the short term to overcome existing problems. However, what usually occurs is that this method develops its own problems. Soils Plant growth is directly affected by the type of soil the plants are grown in. The majority of plants depend on soil to provide nutrition, physical support (ie a place for roots to anchor), water and air. The exceptions to this are those plants known as epiphytes. These grow in such places as tree trunks, on rocks, or on fallen logs. The quality and quantity of plant
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This note was uploaded on 10/24/2011 for the course POLS POLS 333 taught by Professor Evans during the Winter '11 term at Cal Poly.

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Mason1_1 - Soils Introduction The thin layer of soil at the...

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