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In agriculture, green manure is created by leaving uprooted or mown crop parts to wither on a field so that they serve as a mulch and soil amendment.〔(【引用サイトリンク】title=Green manure - Define Green manure at Dictionary.com )〕 The plants used for green manure are often cover crops grown primarily for this purpose. Typically, they are ploughed under and incorporated into the soil while green or shortly after flowering. Green manure is commonly associated with organic farming and can play an important role in sustainable annual cropping systems. ==Functions== Green manures usually perform multiple functions, that include soil improvement and soil protection: * Leguminous green manures such as clover and vetch contain nitrogen-fixing symbiotic bacteria in root nodules that fix atmospheric nitrogen in a form that plants can use. This performs the vital function of fertilization. If desired, animal manures may also be added. :Depending on the species of cover crop grown, the amount of nitrogen released into the soil lies between 40 and 200 pounds per acre. With green manure use, the amount of nitrogen that is available to the succeeding crop is usually in the range of 40-60% of the total amount of nitrogen that is contained within the green manure crop.〔 : * Green manure acts mainly as soil acidifying matter to decrease the alkalinity / pH of alkali soils by generating Humic acid and Acetic acid * Incorporation of cover crops into the soil allows the nutrients held within the green manure to be released and made available to the succeeding crops. This results immediately from an increase in abundance of soil microorganisms from the degradation of plant material that aid in the decomposition of this fresh material. This additional decomposition also allows for the re-incorporation of nutrients that are found in the soil in a particular form such as nitrogen (N), potassium (K), phosphorus (P), calcium (Ca), magnesium (Mg), and sulfur (S). * Microbial activity from incorporation of cover crops into the soil leads to the formation of mycelium and viscous materials which benefit the health of the soil by increasing its soil structure (i.e. by aggregation).〔 :The increased percentage of organic matter (biomass) improves water infiltration and retention, aeration, and other soil characteristics. The soil is more easily turned or tilled than non-aggregated soil. Further aeration of the soil results from the ability of the root systems of many green manure crops to efficiently penetrate compact soils. The amount of humus found in the soil also increases with higher rates of decomposition, which is beneficial for the growth of the crop succeeding the green manure crop. Non-leguminous crops are primarily used to increase biomass. *The root systems of some varieties of green manure grow deep in the soil and bring up nutrient resources unavailable to shallower-rooted crops. * Common cover crop functions of weed suppression. Non-leguminous crops are primarily used (e.g. Buckwheat)〔 The deep rooting properties of many green manure crops make them efficient at suppressing weeds.〔Vasilakoglou, Ioannis, Dhima, Kico, Anastassopoulos, Elias, Lithourgidis, Anastasios, Gougoulias, Nikolaos, and Chouliaras, Nikolaos. 2011. Oregano green manure for weed suppression in sustainable cotton and corn fields. Weed Biology and Management 11:38-48.〕 * Some green manure crops, when allowed to flower, provide forage for pollinating insects. Green manure crops also often provide habitat for predatory beneficial insects, which allow for a reduction in the application of insecticides where cover crops are planted. * Some green manure crops (e.g. Winter wheat and Winter rye) can also be used for grazing.〔 * Erosion control is often also taken into account when selecting which green manure cover crop to plant. * Some green crops reduce plant insect pests and diseases. Verticillium wilt is especially reduced in potato plants.〔Larkin, Robert P., Honeycutt, Wayne, and Olanya Modesto, O. 2011. Management of Verticillium Wilt of Potato with Disease-Suppressive Green Manures and as Affected by Previous Cropping History. Plant Dis. 95:568-576.〕 Incorporation of green manures into a farming system can drastically reduce, if not eliminate, the need for additional products such as supplemental fertilizers and pesticides. Limitations to consider in the use of green manure are time, energy, and resources (monetary and natural) required to successfully grow and utilize these cover crops. Consequently, it is important to choose green manure crops based on the growing region and annual precipitation amounts to ensure efficient growth and use of the cover crop(s). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Green manure」の詳細全文を読む スポンサード リンク
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