Nitrogen, phosphorus, and potassium

The legal basis for the sale of fertilizers throughout the world is laboratory evaluation of content as available nitrogen, phosphorus, and potassium. By convention, numerical expression of the available nutrient content of a fertilizer is by three successive numbers that represent the percent available of N, P20, and K O, respectively. Thus, for example, a 20—10—5 fertilizer contains available nitrogen in the amount of 20% by weight of N, available phosphoms in amount equivalent to 10% of P2O5, and available potassium in amount equivalent to 5% K O. The numerical expression of these three numbers is commonly referred to as the analysis or grade of the fertilizer. Accepted procedures for laboratory analysis are fixed by laws that vary somewhat from country to country. 

Mixed fertilizers contain two or more of the elements nitrogen, phosphorus, and potassium (NPK), which are essential for good plant growth and high crop yields. This subsection briefly addresses the production of ammonium phosphates... 

In hospitals, chemical analysis is widely used to assist in the diagnosis of illness and in monitoring the condition of patients. In farming, the nature and level of fertiliser application is based upon information obtained by analysis of the soil to determine its content of the essential plant nutrients, nitrogen, phosphorus and potassium, and of the trace elements which are necessary for healthy plant growth. 

Growing plants require a variety of chemical elements. Nitrogen, phosphorus, and potassium are required in the greatest amounts, but plants also need trace amounts of calcium, copper, iron, zinc, and other elements. By far the most substantial need is for nitrogen. The Earth s atmosphere is 80% molecular nitrogen, but plants cannot use N2. Instead, most plants absorb nitrogen from the soil in the form of nitrate ions. 

This chapter is concerned with the three primary nutrients making up most fertilizers nitrogen, phosphorus, and potassium. The usual sources of nitrogen are ammonia, ammonium nitrate, urea, and ammonium sulfate. Phosphorus is obtained from phosphoric acid or phosphate rock. Potassium chloride is mined or obtained from brine and the sulfate is mined in small amounts. Potassium nitrate is made synthetically. These chemicals have already been described under inorganic chemicals of the top 50. Sources for the three primary nutrients are given in Fig. 21.1. 

Fertilizers are rated by the percentages of nitrogen, phosphorus, and potassium they contain. 

UREA-AMMONIUM ORTHOPHOSPHATE. A fertilizer developed especially for food-deficient regions, particularly rice-dependent areas. Several grades contain all three primary plant nutrients (nitrogen, phosphorus, and potassium). Contains up to 60% nitrogen, phosphoric anhydride and potassium oxide. 

Asen, S., Stuart, N.W., and Siegelman, H.W. 1959. Effect of various concentrations of nitrogen, phosphorus and potassium on sepal color of Hydrangea macrophylla. Am. Soc. Hort. Sci. 73 495-502. 

Flowever, if only a simple approach to establish the juice content of a drink is used, such as assessing the levels of nitrogen, phosphorus and potassium, it is easy for an unscrupulous supplier to circumvent this method of assessment by the addition of potassium and ammonium phosphate salts, which enhances the nominal juice content of the product. 

Some of the ammonia produced by the Haber process is used to produce nitric acid. If ammonia is then reacted with the nitric acid, we have the basic reaction for the production of many artificial fertilisers. The use of artificial fertilisers is essential if farmers are to produce sufficient crops to feed the ever-increasing world population. Crops remove nutrients from the soil as they grow these include nitrogen, phosphorus and potassium. Artificial fertilisers are added to the soil to replace these nutrients and others, such as calcium, magnesium, sodium, sulfur, copper and iron. Examples of nitrogenous fertilisers (those which contain nitrogen) are shown in Table 11.7. 

Plants need nitrogen, phosphorus and potassium for their growth. The soil is normally able to provide these nutrients to plants. When the same crops are grown over and over again, the soil loses these essential nutrients. Chemical fertilizers help to sustain or in some cases revive the fertility of the soil. 

Phosphorus containing fertilizers Phosphates are the basic substances in these fertilizers. Phosphorus is also essential for plants. Phosphorus compounds are produced by powdering rock phosphate and adding sulfuric acid to it. The resulting products - phosphoric acid and calcium salts (from the rock) are directly applied to the soil to increase its phosphorus content. Potassium fertilizers examples Potassium chloride, Potassium nitrate etc. A complete fertilizer contains nitrogen, phosphorus and potassium in a fixed ratio. This is called NPK fertilizer. 

Varley, J. A. Automatic Methods for the Determination of Nitrogen, Phosphorus and Potassium in Plant Material. Analyst 91, 119 (1966). 

The most popular fertilizers contain the three major nutrients nitrogen, phosphorus, and potassium, and they are therefore referred to as NPK fertilizers. To illustrate their importance in any economy, in 2000, the world consumption of the total fertilizer nutrient (N + P205 + K20) was 140... 

The major use of phosphate is to supply phosphorous, one of the three essential plant foods, nitrogen, phosphorus, and potassium. Phosphate rock extraction from its ore, and its subsequent conversion into fertilizer materials and industrial chemicals, is a relatively mature art. Single superphosphate, a mixture of monocalcium monohydrate and gypsum formed by the reaction of sulfuric acid with phosphate rock, has been used as a fertilizer since the mid-1800s. Phosphoric acid, derived by the treatment of phosphate rock with sulfuric acid so as to produce gypsum in a separable form, was manufactured in many locations by batch and countercurrent decantation methods in the 1920s. 

Usually, three numbers are used when giving the grade of a fertilizer product, and these three numbers always refer in order to the content of the primary nutrients nitrogen, phosphorus, and potassium. If other nutrients are present, their content can also be indicated in the grade of the fertilizer product each extra number is followed by the chemical symbol of the nutrient it represents. Many countries indicate the content of phosphorus and potassium not in the elemental form but in the oxide form, P205 and K20. Thus, a fertilizer product with a grade of... 

Ammonia in Multinutrient Fertilizers. All the ammonia-based fertilizers discussed thus far contain only one of the three major plant nutrients, namely nitrogen. Referring again to Fig. 24.8, one may see that ammonia is the source of fertilizer nitrogen also, either directly or via nitrogen solids or solutions, in multinutrient fertilizers. These are fertilizers that contain two or three of the major plant nutrients—nitrogen, phosphorus, and potassium. Ammonium phosphates, both mono- and di-,... 

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