Soils
Published on Nov 18, 2015
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PRESENTATION OUTLINE
Quick facts
Clay soils are heavy, high in nutrients, wet and cold in winter and baked dry in summer
Sandy soils are light, dry, warm, low in nutrients and often acidic
Silt soils are fertile, light but moisture-retentive, and easily compacted
Loams are mixtures of clay, sand and silt that avoid the extremes of each type
Peat soils are very high in organic matter and moisture
Chalky soils are very alkaline and may be light or heavy
Photo by blmiers2
The different soil types
Soils vary enormously in characteristics, but the size of the particles that make up a soil defines its gardening characteristics:
Clay: less than 0.002mm
Silt: 0.002-0.05mm
Sand: 0.05-2mm
Stones: bigger than 2mm in size
Chalky soils also contain calcium carbonate or lime…
Photo by james_gordon_losangeles
Clay soils have over 25 percent clay. Also known as heavy soils, these are potentially fertile as they hold nutrients bound to the clay minerals in the soil. But they also hold a high proportion of water due to the capillary attraction of the tiny spaces between the numerous clay particles. They drain slowly and take longer to warm up in spring than sandy soils. Clay soils are easily compacted when trodden on while wet and they bake hard in summer, often cracking noticeably. These soils often test the gardener to the limits, but when managed properly with cultivation and plant choice, can be very rewarding to work with
Photo by A Guy Taking Pictures
Sandy soils have high proportion of sand and little clay. Also known as light soils, these soils drain quickly after rain or watering, are easy to cultivate and work. They warm up more quickly in spring than clay soils. But on the downside, they dry out quickly and are low in plant nutrients, which are quickly washed out by rain. Sandy soils are often very acidic
Photo by blavandmaster
Silt soils, comprised mainly of intermediate sized particles, are fertile, fairly well drained and hold more moisture than sandy soils, but are easily compacted
Photo by jenny downing
Loams are comprised of a mixture of clay, sand and silt that avoid the extremes of clay or sandy soils and are fertile, well-drained and easily worked. They can be clay-loam or sandy-loam depending on their predominant composition and cultivation characteristics
Photo by Sprengben [why not get a friend]
Peat soils are mainly organic matter and are usually very fertile and hold much moisture. They are seldom found in gardens
Photo by nosha
Chalky or lime-rich soils may be light or heavy but are largely made up of calcium carbonate and are very alkaline
Photo by milena mihaylova
Where building or landscaping has mixed up different soils, it can be very difficult to tell what type of soil you have, and it may change markedly over a short distance.
Photo by blmiers2
Identifying your soil type
Photo by angela7dreams
Sandy soil has a gritty element – you can feel sand grains within it, and it falls through your fingers. It cannot be rolled to make a sausage shape. If it is not a coarse sand and perhaps a sandy loam it may stick together better
Photo by Massimo Valiani
Clay soil has a smearing quality, and is sticky when wet. It is easily rolled into a long thin sausage and can be smoothed to a shiny finish by rubbing with a finger. If is it not a heavy clay it won’t get quite as shiny and be as easy to make a shape.
Photo by Stuck in Customs
Pure silt soils are rare, especially in gardens. They have a slightly soapy, slippery texture, and do not clump easily
If soil froths when placed in a jar of vinegar, then it contains free calcium carbonate (chalk) or limestone and is lime rich.
Photo by marcp_dmoz
Another important aspect of soil type, is the pH (acidity or alkalinity). This will also affect the type of plants you can grow and how you manage your soil.
Photo by Stuck in Customs
Red soil
Red soil is any of a group of soils that develop in a warm, temperate, moist climate under deciduous or mixed forests and that have thin organic and organic-mineral layers overlying a yellowish-brown leached layer resting on an illuvial (see illuviation) red layer. Red soils generally form from iron-rich sedimentary rock. They are usually poor growing soils, low in nutrients and humus and difficult to cultivate. Red soils denote the second largest soil group of India covering an area of about 6.1 lakhs sq. km (18.6% of India's area) over the Peninsula from Tamil Nadu in the south to Bundelkhand in the north and Rajmahal hills in the east to Kachchh in the west. They surround the black soils on their south, east and north.
Photo by VinothChandar
BLACK SAND
Photo by Justin Mclean
Black sand is sand that is black in color. One type of black sand is a heavy, glossy, partly magnetic mixture of usually fine sands, found as part of a placer deposit. Another type of black sand, found on beaches near a volcano, consists of tiny fragments of lava.
While some beaches are predominantly made of black sand, even other colour beaches (e.g. gold and white) can often have deposits of black sand, particularly after storms. Larger waves can sort out sand grains leaving deposits of heavy minerals visible on the surface of erosion scarps.
Photo by Claudio.Ar
Traditional techniques in Lanzarote use the properties of the natural black Sand to help trap water.
Photo by marcp_dmoz
Despite a climate comparable to the nearby Sahara desert, Lanzarote farmers produce a wide variety of food (fruit, maize, wheat, onions, potatoes, goat fodder etc.) using only a meager average annual rainfall of 150mm. This is made possible by the use of stone mulch, a protective soil covering at least 1.0cm deep. Most commonly this consists of lapilli’s. This is lightweight volcanic gravel known locally as picon. In one region a layer of coarse sand is exploited with similar results.
Photo by kevin dooley
PREVENTING EVAPORATION
Photo by Λլȩҗற୦ட™ (Alexandre Moleiro)
Canary Island geographies and tourist guides often suggest that picon works by somehow extracting dew from the air and adding it to the soil. This is unlikely, as the theoretical maximum dewfall is far less than the minimum daily evaporation. What I believe to be the true explanation of picon’s remarkable effects is a little more complex (but at least conforms to the laws of thermodynamics).
Photo by tim caynes
The theoretical dew Is theory the max amount of water that will precitate from the atmosphere.
Photo by drbob97
Picon aids infiltration of a heavy rain but afterwards forms a capillary break which almost eliminates subsequent evaporation from the soil. This is so effective that a worthwhile crop can be grown in a prepared (i.e. weeded and leveled) stone mulched field even if the rains fail, using water stored in the soil from the year before.
Photo by Alyssa L. Miller
In Lanzarote’s climate, no other type of mulching material compares in terms of preventing evaporation, high soil temperatures and erosion. Although picon adds no new minerals directly to the soil, it improves soil conditions, preserving soil life and so conserving existing nutrients.
Photo by ericthehalibut
Picon also forms a barrier against weed germination. Any weeds that do emerge can be removed by a very light hoeing of the picon; zero till cultivation is possible without herbicides. A hand plough, or one drawn by a single donkey or camel, is sufficient to make furrows for planting as these only penetrate the mulch layer.
Photo by Frank Wuestefeld
In non-irrigated fields, there is no advantage to having a closed crop canopy to shade out weeds, so there is typically wide spacing of individual plants (appropriate to the amount of soil moisture). This in turn enables moist air around the sides of a plant to be constantly replaced; giving side (in addition to top) leaves the opportunity to directly absorb dew and mist, useful but overlooked sources of water. The importance local farmers place on these has been confirmed by experiments in Israel showing 100% improvement in crop yield attributable to foliar absorption of dew.
Photo by Stuck in Customs
Cheap EC Imports have dealt a body blow to local farming. Unfortunately there is another problem ahead; when used for trees or grapevines picon seems to have an unlimited life, but when harvesting annual crops the picon becomes mixed with the underlying clay. This eventually spoils the capillary break on which the suppression of evaporation depends.
Photo by Stuck in Customs
Depending on the type of crop and the amount of care taken, a layer of picon has a useful life of between 20-100 years. At present rates of use, picon supplies will run out m about twenty years. Any ideas for an economical method of renovating old picon would be timely. Both winnowing and washing are effective but obviously not practical on a large scale.
Photo by GGL1
