What's nutirient cycling and give an example?

Question

(this is for science class-plz explain in your own words in a few sentances, and please dont copy and paste those long useless websites that have like nothing to do with waht im talking about or that dont even answer the question. i dont know about you, but its really anoying
thanks : )

Answer 1

☺Here, pick what you want as you are picky. Soil fertility is maintained when nutrients are efficiently recycled through the soil food web and the soil-plant-animal system. Nutrient cycling is conveniently illustrated indiagrams that can range from very simple (see ‘Basic Plant Nutrient Cycle’ below) to extremely complex (see ‘Nitrogen Cycle’ on the next page). Basic Plant Nutrient Cycle. The basic nutrient cycle highlights the central role of soil organic matter. Cycling of many plant nutrients, especially N, P, S, and micronutrients, closely follows the Carbon Cycle. Plant residues and manure from animals that are fed forage, grain, and other plant-derived foods are returned to the soil. This organic matter pool of carbon compounds becomes food for bacteria, fungi, and other decomposers. As organic matter is broken down to simpler compounds, plant nutrients are released in available forms for root uptake and the cycle begins again. Plant-available nutrients such as K, Ca, Mg, P, and trace metal micronutrients are also released when soil minerals dissolve.The Nitrogen Cycle is the most complex nutrient cycle. N exists in many forms, both chemical and physical, so transformations between these forms make the N-cycle resemble a maze rather than a simple, circular cycle. Chemical transformations of N, such as nitrification, denitrification, mineralization, and N-fixation are performed by a variety of soil-inhabiting organisms. Physical transformations of N include several forms that are gases which move freely between soil and the atmosphere. Although the N-cycle is very complex, it is probably the most important nutrient cycle to understand. There are two reasons for this: 1) N is usually the most limiting factor for plant growth in terrestrial ecosystems, so there is often a very large crop yield response to additional N, and 2) N in the nitrate form is very soluble and one of the most mobile plant nutrients in the soil, so it can easily be lost from farm fields and become a contaminant in surface waters or groundwater. Managing N is a critical part of soil fertility Nutrient management is defined as the efficient use of all nutrient sources and the primary challenges in sustaining soil fertility are to: 1) Reduce nutrient losses, 2) Maintain or increase nutrient storage capacity, and 3) Promote the recycling of plant nutrients. In addition, cultural practices that support the development of healthy, vigorous root systems result in efficient uptake and use of available nutrients. Many management practices help accomplish these goals, including establishing diverse crop rotations, growing cover crops, reducing tillage, managing & maintaining crop residue, handling manure as a valuable nutrient source, composting & using all available wastes, liming to maintain soil pH, applying supplemental fertilizers, and routine soil testing. These beneficial cultural practices have multiple effects on the soil fertility factors described above, which makes it important to integrate their use and examine their effects on the complete soil-crop system rather than just a single component of that system. Growing a variety of crops in sequence has many positive effects. In a diverse rotation, deep-rooted crops alternate with shallower, fibrous-rooted species to bring up nutrients from deeper in the soil. This captures nutrients that might otherwise be lost from the system. Including sod crops in rotation with row crops decreases nutrient losses from runoff and erosion and increases soil organic matter. Growing legumes to fix atmospheric N reduces the need for purchased fertilizer and increases the supply of N stored in soil organic matter for future crops. Biologically-fixed N is used most efficiently in rotations where legumes are followed by crops with high N requirements. Rotating crops also increases soil biodiversity by supplying different residue types and food sources, reduces the buildup and carryover of soil-borne disease organisms, and creates growing conditions for healthy, well-developed crop root systems. Growing cover crops can be viewed as an extension of crop rotation and provides many of the same benefits. Growing legume cover crops adds biologically-fixed N. The additional plant diversity with cover crops stimulates a greater variety of soil microorganisms, enhances carbon and nutrient cycling, and promotes root health. The soil surface is covered for a longer period of time during the year, so nutrient losses from runoff and erosion are reduced. This longer period of plant growth substantially increases the capture of solar energy and the amount of plant biomass produced, which in turn increases organic matter additions to the soil. This organic matter is a pool of stored energy in the soil, in addition to a nutrient storage pool, and is the food and energy source for soil organisms. If you look at a farming system as an ‘ecosystem’, and measure the health or productivity of that ecosystem by its harvest of solar energy, then cover crops increase the health of farming systems by increasing the flow of energy and productive capacity through them. The extended growth period obtained with cover crops also extends the duration of root activity and the ability of root-exuded compounds to release insoluble soil nutrients. A winter cover crop traps excess soluble nutrients not used by the previous crop, prevents them from leaching, and stores them for release during the next growing season. Cover crops can also suppress weeds which otherwise would compete with crops for nutrients. Soil erosion removes topsoil, which is the richest layer of soil in both organic matter and nutrient value. Implementing soil & water conservation measures that restrict runoff and erosion reduces nutrient losses and sustains soil productivity. Tillage practices and crop residue cover, along with soil topography, structure, and drainage are major factors in soil erosion. Surface residue reduces erosion by restricting water movement across the soil and tillage practices determine the amount of crop residue left on the surface. Reduced tillage or no-till maximize residue coverage. Water moves rapidly and is more erosive on steep slopes, so reducing tillage, maintaining surface residue, and planting on countour strips across the slope are recommended conservation practices. As discussed above, rotations and cover crops also reduce erosion. Soils with stable aggregates are less erosive than those with poor structure and organic matter helps bind soil particles together into aggregates. Tillage breaks down soil aggregates and also increases soil aeration, which accelerates organic matter decomposition. Well-drained soils with rapid water infiltration are less subject to erosion, because water moves rapidly through them and does not build up to the point where it moves across the surface. Drainage improvements on poorly drained soils reduce erosion. Improving drainage also decreases N losses from denitrification, which can be substantial on waterlogged soils, by increasing aeration. Returning manure to crop fields recycles a large portion of the plant nutrients removed in harvested crops. On farms where livestock are fed large amounts of off-farm purchased feeds, manure applied to crop fields is a substantial source of nutrient inputs to the whole farming system. However, just as nutrients can be lost from the soil, nutrient losses from manure during storage, handling, and application are both economically wasteful and a potential environmental problem. Soluble nutrients readily leach from manure, especially when it is unprotected from rainfall during storage. Nitrogen is also readily lost through volatilization of ammonia, both during storage and when manure is not incorporated soon after field application. Nutrient losses from manure also occur when it is applied at excessive rates. Analyze manure for its nutrient content and adjust application rates based on crop needs and soil tests. Following heavy manure applications with crops that have high nutrient requirements, especially for N and P, reduces losses and increases nutrient-use efficiency. In addition to nutrient value, manure adds organic matter to the soil and provides benefits such as increased CEC for nutrient retention. In addition to manure, organic amendments such as biosolids (sewage sludge), food processing wastes, animal byproducts, yard wastes, seaweed, and many types of composted materials are nutrient sources for farm fields. Biosolids contain most plant nutrients, and are much ‘cleaner’ than they were twenty years ago, but regulations for farm application must be followed to prevent excessive trace metal accumulation. Composting is a decomposition process similar to the natural organic matter breakdown that occurs in soil. Composting stabilizes organic wastes and the nutrients they contain, reduces their bulk, and makes transportation and field application of many waste products more feasible. On-farm composting of manure and other wastes also facilitates their handling. Most organic materials can be composted, nearly all organic materials contain plant nutrient elements, and recycling all available wastes through soil-crop systems by either composting or direct field application should be encouraged. These practices build up soil organic matter and provide a long-term, slow-release nutrient source. Inorganic byproducts also can be recycled through the soil and supply plant nutrients. Available materials vary by region, but rock powder from quarries, gypsum from high-sulfur coal scrubbers, and waste lime from water treatment plants are among the waste products that have been beneficially used. When considering the agricultural use of any byproduct, a thorough chemical analysis and review of possible regulations should be done to avoid soil contamination problems. Even seemingly benign byproducts should be analyzed and field-tested on a trial basis before using them on a large acreage. Vigorous root systems tap nutrient supplies from a larger volume of soil, so management practices that stimulate root growth increase nutrient uptake. Uptake efficiency by extensive, well-distributed root systems results from increases in the amount of root surface area in contact with the soil. The extent of root-soil contact is only about 1-2% of total soil volume, even in the surface 6-inch layer of soil where root density is greatest. For immobile nutrients like phosphorus, root growth to the nutrient is very important. In most soils, phosphate will only move a few millimeters toward a root over the entire growing season. Root-soil contact is determined by root length, root branching, and root hairs. Root hairs are located just behind the root tip and have a relatively short life span of a few days to a few weeks. Actively growing feeder roots are necessary to continually renew these important locations for nutrient uptake. Nutrient absorbing capacity is also increased by symbiotic associations between soil fungi and plant roots. These fungi, called mycorrhizae, function as an extension of plant root systems. Mycorrhizae obtain food from plant roots and in return increase the nutrient absorbing surface for the plant through their extensive network of fungal strands. Mycorrhizae are particularly important for phosphorus uptake and can increase zinc and copper uptake as well. Root activity also has direct effects on nutrient availability in the soil. Insoluble nutrients are released and maintained in solution by the action of organic acids and other compounds produced by roots. Nutrients are also released because the soil immediately adjacent to roots, the rhizosphere, often has a lower pH than the bulk soil around it as a consequence of nutrient uptake. The rhizosphere stimulates microbial activity and microbes also release organic acids and other compounds that solubilize nutrients. A number of soil factors and management practices affect root growth, distribution, and health. Compacted soil layers restrict root penetration, low pH in the subsoil can restrict rooting depth, water saturation and poor aeration inhibit root growth, and roots will not grow into dry zones in the soil. Alleviating these conditions through some of the management practices described above can increase nutrient uptake. Cultural practices that maintain soil biodiversity promote healthy root systems, since an active and diverse microbial population competes with root pathogens and reduces root disease. Soil pH has strong effects on the availability of most nutrients. This is because pH affects both the chemical forms and solubility of nutrient elements. Trace metals such as Fe, Zn, and Mn are more available at lower pH than most nutrients, whereas Mg and Mo are more available at higher pH than many other nutrients. The ideal soil pH for most crops is slightly acid, about 6.3-6.8, because in that range there is well-balanced availability for all nutrients. This pH range is also optimum for an active and diverse soil microbial population. Some crops grow better at higher or lower soil pH than 6.3-6.8, usually because of specific nutrient requirements. Blueberries grow best around pH 4.5-4.8 and are Fe deficient when the pH is much over 5. Most crops suffer from Al, Fe, or Mn toxicity when soil pH is that low. Legumes do best at a higher pH than most other crops, due to the high requirement for Mo by N-fixing bacteria. Limestone is the most commonly used material to increase soil pH. Liming also supplies Ca and dolomitic lime supplies Mg as well. Liming rates depend upon the buffering capacity of a soil in addition to the measured pH. Buffering capacity, or ability to maintain pH within a given range, is related to CEC and increases as clay and/or organic matter content of the soil increases. The lime requirement to raise soil pH the same amount is much larger for fine-textured, high organic matter soils than for coarse-textured, sandier soils. Low soil pH is a more common problem than a pH that is too high, but reducing pH may be necessary for acid-loving plants. Elemental S is the most commonly used material to lower soil pH. Many materials can be applied to soil as sources of plant nutrients, but the term ‘fertilizer’ is usually used to refer to relatively soluble nutrient sources with a high-analysis or concentration. Commercially available fertilizers supply essential elements in a variety of chemical forms, but most are relatively simple inorganic salts. Advantages of commercial fertilizers are their high water solubility, immediate availability to plants, and the accuracy with which specific nutrient amounts can be applied. Because they are relatively homogeneous compounds of fixed and known composition, it is very easy to calculate precise application rates. This is in contrast to organic nutrient sources which have variable composition, variable nutrient availability, and patterns of nutrient release that are greatly affected by temperature, moisture, and other conditions that alter biological activity. The solubility of commercial fertilizers can also be a problem, because soluble nutrients leach when applied in excess or when large rains occur soon after fertilizer application. Increasing soil cation exchange capacity by increasing organic matter reduces the leaching potential of some nutrients. Management practices that synchronize nutrient availability with crop demand and uptake also minimize leaching. Both application timing and the amount of fertilizer are important. Splitting fertilizer applications into several smaller applications rather than a single, large application is especially important on sandy, well-drained soils. Excess nutrient applications can be eliminated or at least significantly reduced by soil testing on a regular basis, setting realistic yield goals and fertilizing accordingly, accounting for all nutrient sources such as manure, legumes, and other amendments, and using plant tissue analysis as a monitoring tool for the fertilizer program.☺