Secondary Nutrients and Micronutrients

Several classes of elements are routinely analyzed in fertilizers. Secondary nutrients and micronutrients in fertilizers are two classes of trace elements beneficial to plants. Common micronutrients analyzed in fertilizers are Zn, Mn, B, Fe, Mo, and Cu, and secondary nutrients include Ca, Mg, and S. 

Secondary nutrients and micronutrients usually are expressed on an elemental basis althou calcium and magnesium sometimes are ejq ressed in the oxide form. However, several countries express all plant nutrients on an elemental basis. Plante actually use neither tile pure element nor the pure oxide form, so the difference is largely academic. Conveireion factors for those plant nutrients that may be expressed in the elemental or oxide form, depending on the country, are shown in Table 1.2. 

Increased knowledge about secondary nutrients and micronutrients, including plant requirements, nutrient sources, and methods of application, has resulted in th increased use. Improvements In soil testing and plant analyses have provided more knowledge about plant needs and the unde variations in plant responses to these nutrients. Higher crop yields and the use of h h-analysis NPK fertilizers also have resulted in increased needs for these nutrients. 

In what form do plants usually absorb phosphorus What are the secondary nutrients and the micronutrients for plants ... 

Secondary and Micronutrients in Fertilizers The great majority of farm fertilizers are produced, marketed, and appHed with regard only to the primary plant nutrient content. The natural supply of secondary and micronutrients in the majority of soils is usually sufficient for optimum growth of most principal crops. There are, however, many identified geographical areas and crop—soil combinations for which soil appHcation of secondary and/or micronutrient sources is beneficial or even essential. The fertilizer industry accepts the responsibiHty for providing these secondary and micronutrients, most often as an additive or adjunct to primary nutrient fertilizers. However, the source chemicals used to provide the secondary and micronutrient elements are usually procured from outside the fertilizer industry, for example from mineral processors. The responsibiHties of the fertilizer producer include procurement of an acceptable source material and incorporation in a manner that does not decrease the chemical or physical acceptabiHty of the fertilizer product and provides uniform appHcation of the added elements on the field. 

Of course there is a loss of information in the study of secondary and micronutrients (Ca, Mg, B, Fe, Mn, Cu and Zn). On the other hand the study would still be able to show whether the soils can supply these nutrients adequately to support any increased yield of grass due to the fertilisers or else that the grass becomes depleted in these nutrients. 

There are thirteen mineral nutrients that plants obtain from the soil, and these are divided into the categories of macronutrients and micronutrients. The primary macronutrients include nitrogen, phosphorus, and potassium. Plants require these primary macronutrients in relatively large quantities and deplete them from the soil more rapidly than others. The secondary macronutrients include calcium, magnesium, and sulfur. Micronutrients are required in smaller quantities than the macronutrients, and these include boron, copper, iron, chloride, molybdenum, manganese, and zinc. 

Nine plant nutrients are required in relatively large amounts and are referred to as major elements or macronutrients. Of these, carbon, hydrogen, and oxygen are obtained from the carbon dioxide in the atmosphere and water and therefore are not dealt with as nutrients by the fertilizer industry. These three plant nutrients make tqa 90%-95% of the dry matter of all plants. The other major elements are subdivided into primary nutrients (nitrogen, phosphorus, and potassium) and secondary nutrients (calcium, magneaum, and sulfur). The remaining seven plant nutriente are required in much smaller amounts and are known as micronutrients or minor elements. 

Plants need other nutrients as well-such as the secondary nutrients (calcium, magnesium, and sulfur) and the micronutrients (boron, chlorine, copper, iron, manganese, molybdenum, sodium, vanadium, and zinc)-but these are needed in smaller quantities and rarely need replenishment in soils. 

---