Transcript Slide 1
As rocks break down mineral ions are released in soluble form Held on surface of small particles Can be accessed by root hairs They are held in organic matter In living or dead organisms Waste products Finally as humus Released as ions (anions and cations) Available for other organisms Plant nutrients Rocks break down as result of: Wind, water Seismic movement Molecules removed from outer surface of particles Are held in solution around the particle Will wash away (by leaching) or Can be taken up by plants (and other organisms) Returned to soil afterwards by decomposition Forms what we call soil! Retained by: Becoming attached to soil particles or in solution Being held in humus Clay and humus have negatively charged sites Sites hold positively charged ions on their surfaces This protects the ions from leaching and loss CEC is the measure of the ability to retain soluble ions in the plant root zone. These ions are rapidly exchangeable with other soluble ions When root uptake depletes the nutrient supply they replenish plant-available cations in the soil solution. Cation exchange is a major source of nutrients e.g. Major nutrient K+, Ca2+, and Mg2+, Ammonium NH4+ Micronutrient trace metals like Zn2+, Mn2+, and Cu2+ The ‘soil cations’ essential for plant growth include ammonium, calcium, magnesium, and potassium. The major distinguishing characteristic of cations is their positive charge. Just like a magnet, a positive charge is strongly attracted to a negative charge. When soil particles have a negative charge, the particles attract and retain cations. These soils are said the have a cation exchange capacity. However, most of the available nutrition is held on the surfaces of fine clay and humus particles. These surfaces, called exchange sites, have a negative charge that attract and bind positively charged minerals, called cations In order to release a cation held on an exchange site, some other material must first dislodge or replace it. This is known as Cation Exchange 150 years research has shown that crops routinely respond well to one set of elements – these are the macronutrients. A 2nd set of elements don’t usually matter, but can cause specific deficiencies. These are the micronutrients. http://apps.rhs.org.uk/advicesearch/profile.a spx?PID=456 Three main elements are need for plant growth: nitrogen (N) to encourage good growth, phosphorus (P) for root growth and potassium (K) for fruit and flowers. N, P, K [big 3] Also Mg, S The micronutrients Ca, Fe, Mn, Mo, Na, Co, Si Crucially important point: It is not enough that a soil contains an element. What matters is its availability to plants. Thus acid digests of heathland soils show ample levels of nitrogen, but almost all of this is locked up in biomass or humic materials, and in fact such soils are acutely deficient in nitrogen. This is the most important plant nutrient, at least in terms of producing a reliable and large increase in growth. Most of the advances in agricultural production since the 1940s have been won by vast increases in nitrogen application. More N => more growth, typically soft fast sappy growth, deep green foliage.. Deficiency of N => stunting, yellowness and general poor growth. This is 2nd in effect after nitrogen. Is always applied as phosphate P deficiency leads to dark, stunted growth often purple tints on the leaves, also causing poor root growth, so limited uptake of other nutrients as well. P promotes cell division, mechanical strength, maturation/seed set, disease resistance. Legumes need littleN (are fixers) but do need P - has been suggested that a major conservation issue in UK is phosphate eutrophication, which leads to N enrichment. Is that it is immensely immobile in soil. This is because many of its salts are highly insoluble, ie bones! Iron, aluminium phosphates are if anything even less soluble. Fe3+ + PO43- => FePO4, insoluble P fertilisers once applied can be locked up in the soil without plants getting any benefit. Acid solutions (such as superphosphate) are the problem: acidity mobilises Fe, Al which them immobilise P. This process is confusingly called phosphorus fixation. This is achieved by controlling soil pH, which should be held around pH 6.5. A prime function of liming acid soils is to elevate the pH to the 6-7 range. Similarly, chalky soils may need to be acidified somewhat to increase P availability, though this is less usual. Soils rich in Fe(OH)3 such as tropical clays will immobilise P whatever the pH trials consistently show K to be a major determinant of plant growth. It determines turgor, frost hardiness and resistance to wind. K deficient plants are stunted and yellow often the older needles / leaves are yellowest as this mobile element is translocated to the newest tissue. Are related to its mobility. Left alone, K will rapidly leach out of soils or litter. It is low on acid sandy or organic soils, highest in clays. Organisms take K up avidly, so that its distribution is ecosystems may be defined by biological not chemical processes. K experiences luxury consumption - this means that plants take up more K than they need if it applied. It does them no harm, but does cost the farmer money. Best fertilise little but often. Causes yellowing, especially of older needles / leaves. Is often caused by waterlogging - a physiological problem not a chemical one. Is cured by adding dolomite (MgCO3+CaCO3) or purer magnesium salts. Carbon (C) Major constituent of all organic molecules, Accounts for around 40% of plant dry matter. Nitrogen (N) Key to protein formation, amino-acids and Enzyme systems. Phosphorus (P) Essential to all living cells for Sugar formation Storage & transfer of energy. Potassium (K) Regulates water movement, plant structure and the transfer of carbohydrates. Sulphur (S) Links with Nitrogen to form protein and is a major part of aminoacids and enzymes. Calcium (Ca) An essential part of cell walls and membranes, protein synthesis and plant defence. Magnesium (Mg) Essential to photosynthesis, chlorophyll, cell repair and metabolism. Boron (Bo) Links to Calcium and Nitrogen uptake, protein synthesis and the formation of hormones, sugars and CHO. Copper (Cu) Involved in protein synthesis, seed formation, plant defence (lignin & phenols) & chloroplast. Iron (Fe) Essential to enzymes involved in respiration, photo-synthesis and disease resistance mechanisms. Manganese (Mn) Vital to photosynthesis, enzymes, cell repair and disease resistance mechanisms. Molybdenunm (Mo) Vital to enzymes needed to regulate and control Nitrogen metabolism. (Nfixing bacteria). Zinc (Zn) Required for starch formation, enzyme systems, phenols and disease resistance mechanisms. Silica (Si) Considered non-essential, but is involved in cell membrane formation and disease resistance. Nitrogen is the most abundant element in our planet’s atmosphere. Approximately 78% of the atmosphere is comprised of this important element. Nitrogen is required by all living organisms for the synthesis of proteins, nucleic acids and other nitrogen containing compounds. The Earth’s atmosphere contains almost 80 % nitrogen gas. It cannot be used in this form by most living organisms until it has been fixed, that is reduced (combined with hydrogen), to ammonia. The nitrogen cycle is a series of processes that convert nitrogen gas to organic substances and back to nitrogen in nature. It is a continuous cycle that is maintained by the decomposers and nitrogen bacteria. The nitrogen cycle can be broken down into four types of reaction and micro-organisms play roles in all of these. http://www.youtube.com/watch?feature=fvw p&NR=1&v=R8-E6cDCr5U http://www.teachersdomain.org/resource/ls ps07.sci.life.eco.nitrogen/ http://www.microbiologyonline.org.uk/about -microbiology/microbes-and-theoutdoors/nitrogen-cycle • • Fertilisers are concentrated sources of plant nutrients, usually in compact form such as pellets, granules, powders or liquids. They are used to improve plant growth and yields. Most fertilisers are based on the three major plant nutrients: Nitrogen (N): For green leafy growth Phosphorus (P): For healthy root and shoot growth Potassium (K): For flowering, fruiting and general hardiness There are many different types of fertiliser available, including liquid tonics that can be applied from a watering can, granular fertilisers that are mixed into compost and powdered feed that is applied to the soil. These feeds work in three main ways: Controlled release fertiliser – ideal for containers, these come as granules that are mixed into compost and release their nutrients over a long period of time, some for up to 12 months. Plugs made from granules bonded together are also available - these can simply be pushed into the surface of the compost. Slow release fertiliser – good for feeding plants in the soil. Usually applied as a powder that can be scattered around perennials, trees, shrubs and vegetables. Fast acting fertiliser – for plants in need of a pick-me-up. These are ideal if a plant is suffering from a deficiency and are usually applied in a liquid form that can be used by the plant quickly. Top dressing Base dressing Watering on: Foliar feeding: http://www.bfs.uk.com/content/BFSNDIGui de.pdf Exercise 2 Work in groups of two List what we can do to alter the nutrient availability in the soil To increase:To decrease:- - http://soils.usda.gov/sqi/publications/files/ biodivers.pdf If you suspect that a plant may be suffering from a nutrient deficiency, but are not certain which nutrient it is, use the symptoms below as a quick reference. To confirm the diagnosis, look up the more detailed descriptions of the symptoms and problem soils etc. under the separate heading for the individual nutrients. Leaves pale green, plants stunted - Nitrogen Leaves with purple or bronze tints - Phosphorus Marginal discolouration/scorch - Potassium Leaves yellow, veins green Iron, magnesium (also see manganese) Dark water-soaked areas on fruit, brown pitting, internal browning, brittle tissue - Calcium or boron Narrowing of leaves (brassicas) - Molybdenum Types of fertiliser Fertilisers are available as solid, liquid or soluble formulations. They may either be quick acting or have a slow or controlled release mode of action. The differences of each type and when to use them are explained below. Inorganic or Chemical fertilisers are available in powder or granular form. They release nutrients readily - but are not quick acting. Organic fertilisers such as blood and bone meal and fish and bone meal are slower acting since they need to be broken down by soil bacteria before the nutrients are available to the plant. Solid fertilisers are generally used as pre-sowing or planting fertilisers or routine top dressings. They are less useful where plants are suffering from a nutrient deficiency because of the time it takes for plants to be able to absorb and then use the nutrients. Solid fertilisers require good soil moisture to transport the nutrients to plant roots. Thus, in dry periods, watering will be necessary. The main benefits of solid fertilisers are their familiarity, ease of application and the fact that they are usually cheaper per unit of nutrient. Are quicker acting, especially if they can be applied as a foliar feed. This is an important consideration when treating nutrient deficiencies. They are a better option in dry weather although in wet weather, the nutrients can be more easily leached through the soil. Contain one key nutrient , are suitable if the crop needs a particular plant nutrient in preference to others, either because of a deficiency problem or if a crop has a particularly high demand for an individual nutrient. These fertilisers are relatively inexpensive and are often used by 'traditional' growers. are available in different formulations to suit different types of users. Some are available as concentrated liquids or soluble powders for dilution by the user. These tend to be more cost effective. are extensively used by plant growers - they are easy to use and effective, provide plants with nutrients for a whole season and release nutrients at times when plants have the greatest demand for them. They are particularly useful for containers and hanging baskets. They are put into the containers at planting time and perform well throughout the season, without the need for supplementary feeding. Nitrogen (N) Nitrogen is an essential nutrient in most plant functions; it is the key constituent in proteins and in chlorophyll and thus is especially important for healthy growth of leaves and other green parts of plants. Good leaf growth is essential for good yields. Deficiency symptoms: Stunted growth, pale green/yellow leaves and general lack of vigour. Symptoms appear on older leaves first. Phosphorus (P) Phosphorus, normally expressed as phosphorus pentoxide (P205) on the label, is important for many plant functions, particularly healthy root growth. It also plays a significant role in encouraging good germination of seeds, seedling development and fruit ripening. Deficiency symptoms: Leaves develop blue/green or purplish tints; dead leaf tissue can occur when deficiency is severe. Leaves are reduced in size. Older leaves are the first to be affected and may drop prematurely. Potassium or Potash (K) Potassium, expressed as potassium oxide (K20) on the label, plays a major role in ensuring high quality and abundant fruit and flowers. Deficiency symptoms: Older leaves are the first to be affected. Symptoms are brown or purple leaf edges and the leaf margins may curl up or downwards. A question of balance When plants suffer from lack of nutrients, they show symptoms of being unhealthy. To allow plant roots to obtain these nutrients from the soil firstly it must be sufficiently moist to allow root uptake. Second, the pH of the soil must be within a certain range for nutrients to be released (see chart on page 6). Third, the soil temperature must be within a certain range for nutrient uptake to occur. The optimum balance of temperature, pH and moisture will differ from one species of plants to another so nutrients may be physically present in the soil, but will not be available to plants. http://www.bfs.uk.com/content/BFSNDIGui de.pdf Macronutrients nitrogen potassium magnesium calcium phosphorus sulphur Micronutrients or Trace elements Iron Zinc Molybdenum Manganese Boron Copper Cobalt Chlorine