Solid fertilisers

Sohd fertilisers are more or less hygroscopic and deliquescent, depending on their composition. In the presence of humidity, the prolonged contact with the granules or fertiliser dust can lead to a pitting attack on aluminium. This attack is slight with nitrate fertilisers, and the more severe the attack is, the richer the fertiliser is in phosphoros. Superphosphates are very aggressive. 

The prolonged storage of aluminium equipment such as irrigation tubes, should be made in a location that is free from fertiliser dust. Otherwise, severe attack of the equipment can be observed during storage. 

Solutions of complete fertilisers (NKP) increase in aggressiveness when their phosphate (P) content is higher. Aluminium will suffer uniform pickling and possibly pitting corrosion. 

Urea solutions, even concentrated, have only a very weak action on aluminium. For example, with a solution of 51 % urea, the annual decrease in thickness amounts to a few micrometers. 

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Nitric phosphate is derived from phosphate rock using nitric acid instead of sulphuric (12.9) (sometimes nitric-sulphuric or nitric-phosphoric acid mixtures are used). The calcium nitrate by-product of this reaction must be removed, or the solid fertiliser would be hygroscopic. One method of achieving this is by crystallisation, and the other is by treatment with ammonia. In the latter instance, a mixture of ammonium phosphate, ammonium nitrate and dicalcium phosphate is obtained (12.10). Alternatively, the calcium nitrate can be converted and the product left in the mixture (12.11). 

Solid fertilisers are usually produced in granular rather than in powder form. Bulk blending of these by mechanical mixing is often practised to produce compound or mixed fertilisers with specific N P K ratios. The principal materials used in bulk blending are ammonium nitrate, ammonium sulphate, urea, superphosphate, ammonium phosphates and potassium chloride. Under EEC regulations, mixed fertilisers are required to have a minimum of 3% N, 5% P2O5 and 5% K2O with the sum of these not less than 20%. 

Abstract This chapter explains the importance of feeding crops and ensuring that soil fertility is maintained. It discusses the main elements required by crops, both major and trace. It explains why liming is so important for crop nutrition. It deals with the calculations and sources of information needed to accurately decide on fertiliser application rates, and cost them. It describes the materials used on-farm as fertilisers and explains the differences between straights, compounds and blends, as well as dealing with liquids and solid fertilisers. There is a section on the use of oiganic manures and slurries and how to make best use of them. Finally, the chapter deals with the effect of fertilisers on the environment, during both their manufacture and application. 

Whilst solid fertilisers are applied by weight (kg/ha) and sold by weight as per 1000 kg, fluid fertilisers are applied by volume (litres/ha) and sold by volume as per 1000 litres (Im ). 

Crystallisation is used for the production, purification and recovery of solids. Crystalline products have an attractive appearance, are free flowing, and easily handled and packaged. The process is used in a wide range of industries from the small-scale production of specialised chemicals, such as pharmaceutical products, to the tonnage production of products such as sugar, common salt and fertilisers. 

It is worthwhile, as a conclusion to this book, to draw a balance of the to date understanding of actinide solids, emphasizing the areas of cross fertilisation with the kindred lanthanide and transition metals fields, and pointing out the new trends and ideas. 

The System Lime and Phosphoric Acid —Solubility of Calcium Phosphates— Conditions of Formation of Basic and Acid Calcium Phosphates—Composition of Solutions Saturated with Calcium Hydrogen Phosphates—Equilibria between Solid Phases and Solutions at Various Temperatures—Changes during Neutralisation—The Acid Phosphates—Manufacture of Superphosphate—Retrogression—Treatment of Special Ores—Phosphoric Acid— Commercial Preparation and Extraction from Rook—The History and Technology of Superphosphate Manufacture—Mixed and Concentrated Phosphorio Fertilisers—Potassium Phosphates—Ammonium Phosphates. 

Many farmers use treated waste from sewage farms as a fertiliser. Some farmers use their own animal waste material to generate methane gas which can be used for domestic and farm heating supplies. Any solid material left is used as a fertiliser. 

The disposal of pig manure poses problems comparable to those of the vegetable waste water. Pre-filtering is even more important here because of the very coarse nature of some of the manure components. As manure from pigs has solids contents as low as 5 to 11%, the main goal is the reduction of the amount to be transported from areas with a manure-surplus to regions with a fertiliser shortage. Very important too, but in the economical sense, is the possibility for disposal of the concentrate of the separation process. Local factors like fertilising limits and the nearby availability of fields that can be fertilised are decisive. 

The solid residue remaining after extraction is to flash dried and sold as animal feed or composted to make fertiliser. It can also be used to generate Biogas. 

The chemistry of the acid aluminium phosphates and their hydrates is complicated. Thermal dehydration of the anhydrous salts leads to condensation and the formation of polyphosphates (5.123), (5.135). Dehydration of the crystalline hydrates can give rise to various mixtures of anhydrous acid phosphates, AIPO4 and amorphous material, depending on the conditions employed. Aluminium acid phosphates have isomorphous iron analogues with which they can form solid solutions. Acid phosphates of iron and aluminium are present in soils and are very much involved in the reactions which take place between soil and fertilisers (Chapter 12.2). Aluminium hydroxide/phos-phoric acid solutions with AI2O3/P2O5 = 1.0-1.5 will give extremely viscous fluids which can be dried down to amorphous solids. Such solids can then be re-dispersed in water to form viscous solutions which are stable under acid conditions. 

The popularity of ammonium phosphate fertilisers arises from their high nutrient content of both P and N, high solubility and good storage and handling characteristics. They are easy to produce and compete economically with the longer-established calcium salts. Commercial products are available as solutions, solids or suspensions. 

F.R. Achorn and H.L. Balay, Solid solution and suspension fertilisers. Chapter 13 in (9). 

Metab. of gorgonian Astrogorgia sp. Inhibits cell division in fertilised starfish eggs. Solid. [(x]jy —16.4 (c, 0.058 in CHCI3). 

More recently polymers have been incorporated directly into liquid and solid based fertilisers, thus giving farmers a greater choice of application technique for the soil stabihser. 

Ammonium nitrate and urea fertilisers are produced by spraying a solution of the fertiliser from a vibrating shower head into a prilhng tower . As the droplets fall down the tower against a stream of cold air they become round and solid, producing prills 1-3 mm diameter. Nitrogen fertihsets in common use are ... 

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