Need For Plant Nutrients ���..an insight

Need and Role of Nutrients in Plant Nutrition

Plants need water, air, light, suitable temperature, and sixteen nutrients to grow. Plants get carbon, hydrogen and oxygen from air and water. The other thirteen nutrients come from the soil. Soil nutrients are divided into two groups according to the amounts needed by plants. The Macronutrients are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. The Micronutrients, which are needed in only trace amounts, are iron, manganese, boron, zinc, copper, molybdenum and chlorine.

These nutrients are essential for plant growth. Plants will grow normally until they run short of one nutrient. Then growth is limited by the availability of that nutrient. Occasionally two or more nutrients will run short at the same time. If the nutrients are deficient, or too abundant, then plants will be discolored or deformed.The deficiency symptoms will indicate which nutrient or nutrients are needed. However, it is much better to supply additional nutrients before deficiency symptoms appear. A soil test will tell which nutrients are low before growth is affected.

FERTILIZING

Most plants in most soils will grow better if additional nutrients are provided by fertilizing. A soil test will give a complete and accurate measure of the nutrients in the soil. A general recommendation is that all soils need more nitrogen. Shallow rooted plants, such as grass and flowers, need more phosphorus and potassium. Acid loving plants, such as rhododendrons, azaleas, camellias, junipers and pin oaks, often need more iron. Sometimes sandy soils need micronutrients, but rarely clay soils. Certain micronutrients may be deficient in certain parts of the country. Many fertilizers are available to supply additional nutrients. Some fertilizers only supply one nutrient. Many supply N, P and K only. A few fertilizers include all of the macronutrients and micronutrients. The label on the package will tell which nutrients are included as well as the sources of the nutrients. The nutrients are identical whether they come from organic or synthetic sources, but the source will affect how fast the nutrients are available to plants. Ammonia sulfate and water soluble fertilizers release most of their nitrogen in a few days and may burn plants if too much is applied. Blood meal releases its nitrogen over a period of months. Organic fertilizers and specially treated synthetic fertilizers release slowly so they last longer and won't burn. Deeper rooting trees and shrubs can be fertilized once a year, but shallow rooted plants, such as grass and flowers, will need regular fertilizing throughout the growing season.

Water can move nitrogen several inches in the soil. Phosphorus and potassium hardly move in the soil.

• There are 16 nutrient elements that have been proven to be essential for the growth and reproduction of plants . Thirteen of these essential elements, which may be supplied by the soil or supplemented by fertilizers, are generally divided into two groups. The macronutrients are nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg). The second group of essential elements is called micronutrients because those elements are required in small (micro) amounts by plants. They include manganese (Mn), iron (Fe), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo), and chlorine (Cl). Although these elements are frequently referred to as minor or trace elements, the term "micronutrient" is preferred.
• Considerable discussion can be generated over what criteria defines an essential element. In the context of this presentation, we caution that the fact that an element is essential does not mean that it needs to be added to soil as fertilizer.
• Since plants obtain carbon, hydrogen, and oxygen from the air and water, there is little control over the availability of these nutrients. For most plants, the dry tissue is composed of 94 percent or more of these three elements. The other 13 elements combined represent less than 6 percent of the plant dry matter. Yet, crop production is frequently reduced and growth limited by a deficiency of one or more of these 13 elements.
• The availability of nutrients to plants from the soil is strongly influenced by various mechanisms of removal, fixation, and release. One of the most important soil properties that affects the availability of nutrients is soil pH, a measure of the acidity or alkalinity of the soil.

Soil Factors That Affect Micronutrient Availability

Physical and chemical characteristics of soil affect the availability and uptake of micronutrients

• Soils low in organic matter (less than 2.0%) may have lower micronutrient availability.
• Soils with higher amounts of clay (fine texture) are less likely to be low in plant available micronutrients. Sandy soils (course texture) are more likely to be low in micronutrients.
• Soils that have very high levels of organic matter (greater than 30% organic matter to a depth of 30 cm) often have low micronutrient availability.
• Soil temperature and moisture are important factors. Cool, wet soils reduce the rate and amount of micronutrients that may be taken up by crops.
• As soil pH increases the availability of micronutrients decreases, with the exception of molybdenum .