In some cases, the soil needs to be raked, also known as scouring, to ensure that the soil is loose to encourage and support rapid growth or topsoil may be applied on top of the existing soil. Clay soils are a lot more problematic. Although they are full of nutrients, clay lacks aeration creating very little oxygen for plant roots to access, while the fine particles mean that plant roots are unable to penetrate the space between them to grow healthy grass.
Chalky soil is one of the worst soil textures for cultivation and revegetation due to its naturally high alkaline properties that cause mineral deficiencies in the soil. In order to reverse this and increase the quality of the soil is to add organic matters in the form of mulches, fibres, fertilizers and added nutrients such as calcium. Cation exchange capacity CEC is the measure of the soils ability to hold positively charged ions.
It is an important soil property that influences the soil structures stability, nutrients availability, soil pH and the reaction of the soil to fertiliser and ameliorants. The organic and clay mineral matter components of soil have negatively charges sites on their surface which hold and absorb positively charged ions cations by electric force.
This is critical to the supply nutrients that vegetation receives because they exist as cations, for example magnesium, potassium and calcium. In general terms, soils with large quantities of negative charge are more fertile because they retain more cations, such as clay soil. Most plants prefer a neutral soil, but some prefer slightly acid or alkaline conditions. Soil pH affects plant growth directly as it determines the availability of nutrients needed to support growth.
Soils with a pH of 7 are identified as neutral. Plant growth and soil processes are favoured by a soil pH range of around 5. In a recent project that was undertaken by Spray Grass Australia, stockpiles were thought to be high in sodium due to the surrounding environment.
OM improves water retention, making it a good addition to sandy soil. OM is also added to clay or silt soils to increase aggregation and thereby improve drainage. Good horticultural soil : Most soils are dominated by mineral particles; some are dominated by organic matter. Some soils have a high percentage by volume of pore space, while others have little pore space. Your soil might vary from one part of your land to another.
At any given time, that pore space is occupied by both air and water. You can assess your soil by irrigating heavily, then allowing it to drain for a day. If the soil is very dry after a day of drainage, it is likely dominated by sand, and you could amend it over time by adding OM. If the soil remains very wet, it is likely dominated by clay or it is not well aggregated; you could amend such a soil over time by adding OM to support aggregation.
Soil chemical activity is related to particle size, because chemical reactions take place on particle surfaces. Small particles have much more surface area than large particles. When salts dissolve into the soil solution, they separate into a cation a positively charged ion and an anion a negatively charged ion. For example, when we dissolve table salt sodium chloride in water, it separates into positively charged sodium and negatively charged chloride ions.
When we add sodium nitrate fertilizer to the soil, it dissolves into the soil solution as sodium cations and nitrate anions. Tiny particles humus and clay are very important for holding plant nutrients in the soil. Clay and humus particles have a negative surface charge. Cations are positively charged. Because opposites attract, the clay and humus hold cations, and prevent them from being leached out of the soil by water movement.
Negatively charged anions remain dissolved in the soil solution, and are very susceptible to leaching downward. Nitrogen is an interesting nutrient, because one nitrogen fertilizer might be positively charged ammonium that is held by soil particles, while another nitrogen fertilizer might contain negatively charged nitrates that remain dissolved in the soil solution. This explains why nitrates, which are anions, leach readily out of our topsoil and sometimes into our water supply.
Ions are constantly exchanged among the soil solution, CEC sites on clay and humus particles, and plant roots. This is not a random process, but is dependent on electron charge. Clay and humus have high CECs because they are tiny particles with very large surface-to-volume ratio, with many negative sites that can attract cations.
Sand has very low CEC because sand particles are large, with low surface-to-volume ratio and hence fewer negative sites. A gardener can add higher rates of fertilizer less frequently when gardening in a soil with a high level of clay or humus, compared to a sandy soil, because cations potassium, calcium, magnesium and others are held by soil particles. Because a sandy soil cannot hold the same amount of cations, fertilizing them more frequently with smaller amounts of fertilizer is a better option.
The pH scale ranges from 0 very acid to 14 very alkaline. Soils generally range from pH 4. Northeastern forest soils can be very acid pH 3. The pH scale is logarithmic; each unit is 10 times more acid or alkaline than the next. For example, a soil with pH 4. Individual plants perform best within specific pH ranges. It is just as important to manage pH as fertility. Most garden plants perform well in a soil with pH 6. Acid-loving plants such as rhododendron and blueberry perform well in a soil with pH below 5.
Many organisms inhabit soil: bacteria, fungi, algae, invertebrates insects, nematodes, slugs, earthworms and vertebrates moles, mice, gophers. These organisms play many physical and chemical roles that affect plants.
For example, their secretions help dissolve minerals, making them available to plants; some organisms convert inorganic substances into other forms that are more or less available to plants; organisms add OM to the soil; organisms help decompose OM; many organisms aerate the soil. Some living organisms in the soil cause diseases, some feed on plant tissue, and many compete with plants for nutrients and water.
Rhizosphere : The very thin zone of soil just around roots is called the rhizosphere. This zone is different from the rest of the soil, and it sometimes supports specific and unique organisms. Similarly, some nitrogen-fixing bacteria grow together with some plants, including many legumes members of the bean family. The bacteria convert atmospheric nitrogen into forms that can be used by their host plants. When the host plant dies, the nitrogen compounds released during decomposition are available to the next crop.
Any mutually beneficial relationship between two dissimilar organisms is called a symbiosis. Water is an amazing substance. It is called the universal solvent because it dissolves more substances than any other liquid. It is a renewable natural resource. It exists in nature as a solid, liquid and gas. Its molecules cohere stick together and adhere stick to to other surfaces; this accounts for its ability to reach the top of tall trees. It has a high latent heat, which means that it releases a large burst of energy when it passes from solid to liquid and from liquid to gas.
And, when it passes from gas to liquid and from liquid to solid, it absorbs a large burst of energy. Gardeners reap the benefits all of these attributes of water. Clayey soils have high water-holding capacity, while sandy soils have low water-holding capacity. Clayey soils drain much more slowly than sandy soils. Loamy soils reach their field capacity days after a heavy rainfall or irrigation.
If no more water is added, the soil continues to dry out; plants take up some of the water, and some water moves upward in the soil and evaporates from the surface. Eventually, a soil may dry enough to reach its permanent wilting percentage , the point at which a plant wilts so severely that it cannot recover.
At this point, the available water water that remains available to the plant is gone, and the only water that remains in the soil is so tightly bound to soil particles that plants cannot access it. Irrigating a heavy clayey soil and a sandy soil in the same way would result in very different results. Good soil management is critical for crop productivity. Poor management can lead to erosion, loss of fertility, deterioration of soil structure, and poor crop yields.
Tilling : Mechanical manipulation of soil loosens the soil, and promotes aeration, porosity and water-holding capacity. It allows a gardener to incorporate soil amendments such as OM and lime. On the other hand, tilling tends to decrease aggregation, causing compaction compacted soils are dominated by few, small pores.
It can take years to overcome the damage caused by overtilling. World food and agriculture: Outlook for the medium and longer term. Bernhard, A. Nature Education Knowledge 2 , 12 Bongaarts, J. Human population growth and the demographic transition. Brady, N. The Nature and Properties of Soil, 13th ed.
Prentice Hall, The Nature and Properties of Soil, 14th ed. Brodt, S. Sustainable Agriculture. Nature Education Knowledge 3 Epstein, E. The anomaly of silicon in plant biology.
Hillel, D. Out of the Earth: Civilization and the Life of the Soil. University of California Press, Johanson, D. Simon and Schuster, New York. Lal, R. Soil-erosion from tropical arable lands and its control. Advances in Agronomy 37 , Lutz, W. The end of world population growth. Nature , Montgomery, D. Dirt: The Erosion of Civilizations. Univeristy of California Press, Soil erosion and agricultural sustainability. Moss, B. Water pollution by agriculture.
Pimentel, D. Environmental and economic costs of soil erosion and conservation benefits. Science , World agriculture and soil-erosion. Bioscience 37 , Price, T. School of American Research Press Schulze, D.
Soil Science Socity of America, Schwartz, G. The University of Arizona Press, Sharpley, A. Introduction: Agriculture as a potential source of water pollution. Agriculture, hydrology and water quality , Singer, M.
Soils: An Introduction , 6th ed. Pearson Education Inc. Subbarao, G. Sodium - A functional plant nutrient. Critical Reviews in Plant Sciences 22 , , doi Tilman, D.
Global environmental impacts of agricultural expansion: The need for sustainable and efficient practices. Agricultural sustainability and intensive production practices. Nature , , doi Trigger, B. Cambridge University Press, Troeh, F. Soils and Soil Fertility , 5th ed. Oxford University Press, Wakatsuki, T. Rates of weathering and soil formation.
Geoderma 52 , Soil: The Foundation of Agriculture. What Are Soils? Food Safety and Food Security. Introduction to the Sorption of Chemical Constituents in Soils. Pests and Pollinators. Soil erosion controls on biogeochemical cycling of carbon and nitrogen. The Influence of Soils on Human Health. Use and Impact of Bt Maize. Aquaculture: Challenges and Promise. Soil Carbon Storage. Soil Minerals and Plant Nutrition. Soil Water Dynamics. The Conservation of Cultivated Plants.
The Soil Biota. Transgenic Animals in Agriculture. Citation: Parikh, S. Nature Education Knowledge 3 10 Throughout human history, our relationship with the soil has affected our ability to cultivate crops and influenced the success of civilizations.
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