Soil Notes PDF

Soil Importance of the soil 1- mechanical support by permitting the plant roots to grow through it 2- It holds water, nutrients and air that are essential for the plant growth. Soil de nition A thin layer of the earth`s crust. - It is unconsolidated mixture of disintegrated rock with:Organic matter-...

Soil Importance of the soil 1- mechanical support by permitting the plant roots to grow through it 2- It holds water, nutrients and air that are essential for the plant growth. Soil de nition A thin layer of the earth`s crust. - It is unconsolidated mixture of disintegrated rock with:Organic matter-Water- Air-microorganisms What is in the soil? Mineral particles of weathered rocks- Water & dissolved mineral salts- Air in spaces between particles-Dead organic matter (humus)- Microorganisms Soil particles from weathering rocks Rocks are gradually breaks down into di erent sizes of soil particles The range of particle sizes; Coarse sand → 2.0 mm - 0.2 mm Fine sand → 0.2 mm - 0.02 mm Silt → 0.02 mm - 0.002 mm Clay → less than 0.002 mm. Soil texture clay silt Loam sand  type of soils 1- Clayey soil Sandy soil (light Loam soil Silt soil (heavy soil) soil) Loam soil is Pore size is a. is composed a.It has large pore composed of equal medium primarily of clay spaces, good amounts of clay Features particles. aeration and fast and sand soils. between b. The ne drainage. However, if the clay clay and particles are at & b.Nutrients are is 30% to the sand, sand disk-shaped and washed away it is called clayey in close contact from the soil by loam and if the with one another. irrigation or clay15% it is called (No pore spaces). rainfall. sandy loam. c. It is moldable c. Heats up A good soil for when wet & hard rapidly and dries gardening should cloddy when dry. up contain: d. It is a poor- d. Particles do not 70% sand drainage soil. 15% silt e. It has a great 10% clay capacity to attract humus & and microorganisms. hold nutrients (minerals). Soil pro le (layers) Every soil has a pro le The pro le is presented by a series of layers in a vertical section from top to bedrock below Layers in this pro le are called horizons Horizons of the pro le di er in color, structure, porosity and consistency. Soil layers (horizons): 1- The 0 horizon (soil surface) 2- The A horizon ( topsoil) 3- The B horizons (subsoil) 4- The C horizon (bedrock or hardpan) 1- The 0 horizon (soil surface). a few centimeters thick. contain most of fallen leaves 2- The A horizon ( the topsoil).It is 10-30 cm below the soil surface.. Contains about 10-15 % organic matter with dark color 3-The B horizons (subsoil) - large soil particles. - little amounts of organic matter - large amount of minerals washed by rainfall from the topsoil. - Mature roots go to B horizon. 4-The C horizon (bedrock or hardpan). It is about 90-120 cm below the soil surface. compacted soil of rock fragments that slows/stops the movement of water, air & the growth of roots into lower layers..It is with no organic matter Soil organisms Nematodes Insects Earthworms Fungi & algae Bacteria Most of soil organisms are bene cial - They form an essential part of soil complex. - They can improve drainage & aeration - They aid in plant nutrients & water uptake. - Some are harmful causing plant injuries or diseases Organic matters in the soil (plants & animals) -When they decomposed they form →→ Humus ‫الدبال‬ -Soils lacking organic matter and humus are light in color. Why humus is important to soil? 1- it holds moisture 2- absorbs & holds plant nutrients 3- it feeds soil organisms. Soil Erosion - It is the movement of soil particles from one place to another by. water (heavy rainfall/ irrigation) wind. - Soil erosion can be controlled by growing plants with extensive, brous roots. Soil pH ( the hydrogen ion concentration in soil) The pH a ects soil characteristics & plant growth Soil acidity is measured with pH scale; 0 ↔14 0 extreme acidic ←→14 extreme alkaline pH of most soils ranges from 4 – 8 Acidic soil pH < 7 Neutral soil pH 7 Alkaline soil pH > 7 The optimum range for the majority of plants to grow is pH 6.5 -7.0 Almost half of crop nutritional problems can be averted by holding pH in the desired range pH controls the availability of nutrients to the plant At low pH Al & Mn in soil water are more soluble At high pH calcium phosphate is less soluble. How to adjust the pH in the soil lime (Ca oxide- inorganic fertilizer) is used to raise soil pH to be more alkaline Inorganic substance e.g. Al sulfate is used to lower soil pH to be more acidic. Soil improvement The soil can be improved by adding amendments. A soil amendment is a material added to the soil to improve the physical properties such as drainage and aeration. The amendment should be used in large amount (about 25% of the volume of the soil). Each type of soil amendment has certain properties and it is used according to the problem of the soil. There are inorganic amendments such as vermiculite and perlite, and organic amendments which include di erent types of compost or humus Soil of the desert 1- Most soils are sandy 2- Some soils are saline due to the presence of Sodium salts which are poisonous to plants. *High salt content in soil is considered as a stress for the plants 3- The temperature of the soil is high/low which is harmful to plants. 4- Poor in some elements (Nitrogen & Phosphorous) 5- Alkaline with high pH. 6- Poor in organic matter 7- Most soils with prominent, whitish layers called calcic horizons *Some areas have excessive amounts of calcium carbonate under the surface in many layers. calcic horizons is caused by the accumulation of calcium carbonate ( chalk), and other materials. It is called caliche - it prevents drainage - The presence of Ca in this layer makes other nutrients (e.g. Fe, Zn) unavailable In some soils, these horizons become very thick (about1m thick) & strongly cemented. The nearly impenetrable, cemented layers, are called hardpan Features of soils in Kuwait Mostly sandy & coarse loamy < 18% clay. Most soils are - calcareous (Ca compounds) to some extent in the rst meter from the surface - with accumulations of carbonate, gypsium & salts in di erent amounts. A common feature of many Kuwait soils is a calcic and/or gypsic pan locally named gatch. When Calcium carbonate & gypsum (calcium sulfate, CaSO4) are precipitated and cemented they form a pan (a horizon), which provides a barrier to plant roots. This horizon is called a petrocalcic (carbonate cemented) or petrogypsic (gypsum-cemented) horizon. Soil of Kuwait contains high concentration of gypsum Many of these soils also contain signi cant amounts of gravels, reducing their ability to hold both water & nutrients for plant growth The Gatch layers are limiting the growth of plants because they are 1- hindering water movement in soils 2- decreasing air proportion in soil pores 3- preventing the extension of plant roots The soil of coastal areas and some depressions are unsuitable for irrigated agriculture due to salinity Soil of Kuwait has pH ~8.5 The presence of salts increases the osmotic pressure in the soil solution. This - decreases water in plants - increases salts in toxic amounts Areas in Kuwait which have suitable soils for irrigated agriculture The area between Kuwait City and Saudi Arabia border - The area east of Al-Abdali. Features of soils that are suitable for irrigated agriculture freely draining - have no restriction to root growth - loose and easy to cultivate - non-saline - non-gypsic - without high concentrations of calcium carbonate in the top 50 to 100 cm. Essential bases for agricultural activity 2-Water 1- Importance of water to plants 2- Water and air in soil 3- Forces of attraction 4- Water availability 5- Water loss 6- Irrigation 7- Drainage  1- Carries the soluble minerals in soil 2- Essential for photosynthesis(PHS) 3- Essential to move the PHS products 4- Essential for transpiration & regulating internal temperature 5- It keeps cells turgid 6- Water is the main content of protoplasm Good soil must contain proper amounts of water and air Sand soil has lots of air but no water Clay soil has lots of water but no air Soil with small pore spaces holds water better. 3- capillarity force 1- adhesion force 2- cohesion force - forces that water - force of attraction - force of held in soil against the between solid attraction among force of gravity material and liquid water molecules e. g. between soil & water Capillarity is one of the major forces that move water Capillarity forces pull water into a narrow tube or any other narrow spaces ) e.g. soil) Capillarity in soil If a pore space is small, a greater amount of water remains due to; Adhesion, cohesion and capillarity Clay has high-holding capacity of water Sand has low-holding capacity of water Field water capacity permanent wilting To calculate water - It is the amount of capacity availability: water held by a soil Permanent wilting after drainage due capacity occur Water availability = to gravity, has been When water Field water capacity − completed. evaporates or permanent wilting - It is the maximum used up by the capacity amount of capillary plant till no water. Water availability is water that a left the highest within clay particular soil is able soil to hold 1- Transpiration 2- Evaporation (water loss from plants) (water loss from soil) - ~90% of water enters a plant, passes * For water to be through & evaporates available, annual rain or through stomata into irrigation must exceed the atmosphere evapo-transpiration Irrigation is watering plants by rainfall or other sources Much of water → lls pore spaces in soil → water logged →→ plant dies Drainage is the rate at which water ows through the soil or potting medium - Poor drainage is recognized by slow water ow & high retention - Good drainage is recognized by fast water ow and low retention 3-Nutrients for Plants Plants obtain a large number of mineral nutrients from the soil. -Apart from carbon, oxygen, and hydrogen, plants need at least 13 di erent chemical elements or nutrients to manufacture the whole range of complex organic compounds. -These elements are acquired by selective absorption from the soil solution. Food production and fertilizers - The yield of the crops over the world need to be increased due to the high increase in human population - Using fertilizers is one of the means to increase food production. Nutrients for plants - In general, soils contain minerals to support growth for most of the plants. - In natural ecosystems, mineral recycling ensure that soil nutrient levels do not change. Why we had to add nutrients to soil? - Over-using & harvesting of the land. - Lacking minerals in most soils. - At certain pH, minerals can react with others in soil forming compounds that can not be used by plants.  The mineral nutrients are grouped into: l 1- Macronutrients: 2- Micronutrients (or trace - Macronutrients are elements elements): that are used in large quantities - Micronutrients are by plants. elements that are used by They include N, P, K, Ca, Mg, plants in small quantities. and S which are the - The most common are constituents of many plant Fe, Cu, Z, B, Mb, CL and components such as proteins, Co. nucleic acids and chlorophyll. - They have a variety of They are essential for some essential functions in plant processes such as energy metabolism. transfer, enzyme function and - Soils should contain the maintenance of internal enough elements to supply turgor pressure. most plants. Ca, Mg, and S are generally - The majority of nutrients present in large quantities in soil are available between pH and need to be added when 6.5 and pH 7. fertilizing. P, K, and N are not present frequently in su cient amounts for optimum growth, they should be contained in the fertilizers. For optimum growth, nutrients must be available in a soluble form, in appropriate and balanced amounts and at the right time in the growing season. - Most agricultural soils contain considerable amounts of nutrients but these are largely tied up in the organic humus or as inorganic ions bound to the clay. - In natural ecosystems the processes of mineral recycling ensure that soil nutrient levels do not change very much from year to year, and although the nutrient supply may limit productivity, the e ect remains relatively constant. - In agriculture and horticulture, the problems of nutrients supply are increased by harvesting, which actively removes nutrients from the site. - This results in the progressive depletion of soil nutrients reserves and the soil becomes poor. The soil nutrient supply becomes insu cient for crop needs and fertilizer application is the only way of maintaining productivity. Fertilizers Fertilizers are the organic or inorganic materials that provide minerals for plant growth.. Fertilizers can be added in many forms but generally classi ed as: Organic fertilizers (e. g. animal residues, plants); they derived from the decomposition of plants and animals. they can act as soil amendments in addition to supplying nutrients. organic fertilizers are not reliable in most areas because their decomposition process is slow especially in cold soils, and synthetic organic fertilizer (e.g. urea) can be used. Inorganic fertilizer (e.g. ammonium nitrate); -they are made from raw material such as natural gas and phosphate rock. -some fertilizers show rapid response by the plant while others release nutrients slowly over a period of time (fast release and slow release). Nutrient in soil & pH - The pH of the soil controls nutrient availability e.g. low pH (below 6) →→ K decreases high pH → N & P uptake is reduced - Most plant nutrients are in their most available state at pH 6.5 -7 - de ciency problems may be caused by pH changes. -Changing the pH may lead to de ciency in minerals. Sources of nitrate & nitrogen xation 1- From air 2- From breaking down of nitrogen containing- compounds from organic matter{Most plants use only nitrate form(NO3-)} 3- Certain bacteria can x N in soil Nitrogen xation Nitrogen- xing bacteria live inside the nodules in a mutually bene cial relationship with the legumes plants Few plants can x nitrogen in soil, with help of these bacteria The advantages & disadvantages of using fertilizers The advantages bigger & better crops can be obtained. without fertilizers, crops would be smaller & more likely to be a ected by diseases The Disadvantages over-use of fertilizers can cause pollution of land and water (rivers, lakes ….) The pollution may a ect badly the organisms living in these places. Eutrophication Eutrophication is the process in which a water body becomes overly enriched with nutrients, lading to plentiful growth of simple plant life. Due to overuse of agricultural fertilizers: 1- nitrates from fertilizers accumulated in watercourses 2- plants and algae grow rapidly 3- the increased growth of the top plants & algae stops sunlight from reaching other organisms growing below in the water 4- the plants die & decomposed by bacteria 5- bacteria use up oxygen creating shortage of oxygen in water. 6- Death of other organisms due to shortage in oxygen