Nutrient Cycling

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Nutrient Cycling
   Page | 1 Agroforestry systems can lead to more closed nutrient cycling, and so to more efficient use of nutrients 1 Md Mezanur Rahman 2  Abstract Plant and Nutrient are indispensable part. The term "nutrition" refers to the interrelated steps by which a living organism assimilates food and uses it for growth and replacement of tissue.  Efficient use of all nutrient sources can be defined by the term “nutrient management”. These are the management practices to maximize nutrient cycling & nutrient-use efficiency. And in management practices, the primary challenge is to sustain soil fertility. For effective growth and development a plant require almost 17 nutrients.   These nutrients may be lost in different ways such as runoff, erosion, leaching, gaseous losses to the atmosphere, crop removal etc. The processes of lost of nutrients from soil are most common in traditional agriculture practices. Most agricultural systems represent “open” or “leaky” systems w ith inputs and outputs sometimes as much as 40% of internal cycling. Natural forest ecosystems represent self- sustaining and efficient nutrient cycling systems. These are “closed” nutrient cycling systems with relatively little loss or gain of the actively cycling nutrients, and high rates of nutrient turnover within the system; inputs and outputs sometimes amounting to less than 10% of internal cycling. In closed nutrient cycling of agroforestry, tree liter fall on the ground, decomposed, mixed with soil, form nutrient and again plant root uptake this from soil thus nutrient loss is minimum and so to more efficient use of nutrient.   Page | 2 Introduction: Goals of effective nutrient management are to provide adequate plant nutrients for optimum growth and high-quality harvested products, while at the same time restricting nutrient movement out of the plant-root zone and into the off-farm environment. Agroforestry practices control nutrient cycling and influence many other aspects of soil fertility. The concept is based on enhancing the capacity of tree root system to trap nutrients in the soil solution that would otherwise be lost by leaching and to recycle them through litter to the soil surface. Knowledge of these processes helps farmers make informed/effective management decisions about their crop and livestock systems. How these decisions affect soil biology, especially microbial activity, root growth and organic matter, are key factors in efficient nutrient management. Managing soil organic matter and biological nutrient flows is complex, because crop residues, manures, mulches of pruning’s, composts, and other organic nutrient sources are variable in composition, release nutrients in different ways, and their nutrient cycling is strongly affected by environmental conditions. Understanding processes helps identify practical options that fit different farming systems. Understanding nutrient cycles helps all types of farmers maintain the fertility of their soils, while at the same time protecting our essential resources. Objective :    To identify the processes by which plant nutrients go through as they cycle through the soil.    To establish an enriched knowledge about how these processes affect nutrient availability to plants and nutrient movement from farm fields to surface or groundwater.    To discover ways to manage crops and soils to maximize nutrient availability and minimize nutrient movement to the surrounding movement and logical judgment of the agroforestry systems in this respect.   Page | 3 MATERIALS & METHODS This term paper is exclusively a review paper so all the information has been collected from the secondary sources. During the preparation of this review paper, the researcher went through various relevant books, journals, proceedings, reports, publications etc. Findings related to the topic have been reviewed with the help of library facilities of Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) and internet searching. All the information collected & compiled has been presented in its present form.   Page | 4 Result and Discussion In a soil-plant system, plant nutrients are in a state of continuous, dynamic transfer. Plants take up nutrients from the soil and use them for metabolic processes. In turn, plants return nutrients to the soil either naturally as litterfall in unmanaged systems, deliberately as prunings in some agroforestry systems, or through root senescence in both managed and unmanaged systems. These plant parts are decomposed by soil microorganisms, releasing the nutrients bound in them into the soil. The nutrients then become available for plant uptake once again. Nutrient Cycling:  The term nutrient cycling, as used in most agroforestry discussions, refers to the continuous transfer of nutrients that are already present within a soil-plant system, such as a farmer’s field (Nair, 1993; Nair et al., 1995; Sanchez and Palm, 1996; Buresh and Tian, 1997). However, in a broader sense, nutrient cycling involves the continuous transfer of nutrients within and between different components of an ecosystem and includes processes such as weathering of minerals, activities of soil biota, and other transformations occurring in the biosphere, lithosphere, and hydrosphere (Jordan, 1985). Or, the nutrient cycle consists of stores, flows within the system, and gains and losses external to it. The nutrient stores are tree and crop shoots and roots, plant residues soil fauna, labile and stable soil organic matter, secondary clay minerals (through fixation) and the store of available nutrients in mineral form in the soil solution. The main internal flows are from the plant components to plant residues, via soil fauna to soil humus, through the process of mineralization to mineral nutrients, and return to the plants via root uptake. Figure 1: Nutrient Cycling     Page | 5 Inputs of Plant Nutrients in the Soil Plants obtain mineral nutrients through root uptake from the soil solution. Sources of these soluble nutrients in soil include:    Decomposition of plant residues, animal remains, and soil microorganisms    Weathering of soil minerals    Fertilizer applications    Manures, composts, biosolids (sewage sludge), kelp (sea weed), and other organic amendments such as food processing byproducts    N-fixation by legumes    Ground rock products including lime, rock phosphate, and greensand    Atmospheric deposition, such as N and S from acid rain or N-fixation by lightning discharges    Deposition of nutrient-rich sediment from erosion and flooding Figure 2: Inputs of Plant Nutrients in the Soil
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