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A plant needs at least 17 elements to grow and reproduce. Hydrogen, oxygen and carbon are supplied by the environment, the other fourteen are supplied by the soil.

Elements that are required by plants in relatively large amounts are called macronutrients elements that are required in smaller amounts are called micronutrients. Each element has one or more specific functions in plant metabolism.

The study of the ability of the soil to supply and sustain adequate amounts of nutrients for plant growth is called soil fertility. How plants take up nutrients and use them in their metabolism is called plant nutrition. Many soil physical and chemical characteristics affect the availability of nutrients to plants. The nutrient cycle   determine the long term sustainability of fertility. But in the short term, the chemical form of the nutrient in the soil, how it moves to the plant root (ion movement) through the pore space of soils is most important. Nutrient deficiencies can usually be corrected with the addition of chemical or natural organic fertilizers. However, before we can know how much fertilizer to apply, nutrient deficiency can be qualified by chemical analysis of growing crops or soil testing after harvest, or better, just prior to seeding.

Essential Nutrients These are nutrient elements that fulfill two conditions

1. Nutrient is directly involved in the metabolism of the plant.

2. Nutrient can not be substituted by another element.

Essential elements are usually divided into two categories depending on their concentrations with the plant tissues: macronutrients and micronutrients.

Macronutrients These are nutrients that are required by plants in relatively large amounts and include the three supplied by the atmosphere carbon, hydrogen and oxygen and six supplied by the soil: nitrogen, phosphorus, potassium, calcium, magnesium, sulphur. Most cultivated soils are deficient in nitrogen and phosphorus and require annual additions of these two fertilizers to remain productive. Potassium and sulphur deficiencies once concentrated in the poorer northern soils are spreading. Pulse and oil crops which are replacing cereals require more sulphur and potassium. Only a few soils require the alkaline elements of calcium and magnesium since most of our soils were formed on glacial till deposits that were rich in limestones.

Micronutrients These are elements plants require in relatively small amounts and include seven are recognized as being essential for all plants: chlorine, iron, boron, manganese, zinc, copper, molybdenum and nickel. Four other are essential for only some plants or are required by bacteria in symbiotic association with the plant: sodium, cobalt, vanadium and silicon. Although these nutrients are required in much smaller quantities than macronutrients by a factor of 10 to 1000 times less, nonetheless they are just as important and crop yield and quality will suffer if the plant is deficient in these nutrients.

Fertilizer Forms Soils under intensive crop or animal production lose nutrients. Losses are to the ground water through leaching and to the atmosphere through the volatilization. We must also consider that the harvested crop or grazing animal takes away nutrients from the soil. Modern farming requires the regular addition of plant nutrients to supplement the nutrient supplying power of soils and maintain high yields. These nutrients are contained in natural (organic) or chemical fertilizers, which must be applied in a careful and timely manner. Fertilizers can be applied in many forms.

Soil and Plant Testing Adding too much fertilizer has been a problem in many countries that have intensive agriculture production. Mobile nutrients such as nitrogen can move out of the soil profile into the underground aquifers and may contaminate our drinking water and rivers.

4.4 Give English equivalents: плодородие почвы, движение ионов, органические удобрения, большое количество, ежегодные добавки, щелочные элементы, основные компоненты почвы, минеральные вещества, выщелачивание, собранный урожай, современное земледелие, питьевая вода.

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