Blending fertilisers

Micronutrient fertilisers can be made by incorporating snitable micronutrient compounds into bulk-blended fertilisers. Boron phosphate, BPO4, is an excellent slow-release source of boron. Relatively insoluble crystalline mixed-metal potassium polyphosphates can also be used. Micronutrient phosphate glasses also have valuable slow-release characteristics (Section 12.9). The required metals are introduced into the very sUghtly water-soluble glasses in the form of their oxides, for example, ZnO, CuO, MnOj, M0O3 or BjOj [37] (Table 12.26). 

G. Hoffmeister and G. H. Megar, "Use of Urea iu Bulk Blends," Proceedings of the 25th Finnual Meeting of the Fertiliser Industry Round Table, Washington, D.C., 1975, pp. 212-226. 

G. Hoffmeister, Proceedings of the TFLti Fertiliser Fulk Blending Conference, TVA Bulletin Y-62, Tennessee Valley Authority, NFDC, Muscle Shoals, Ala., pp. 59—70. 

Agricultural uses for ammonium thiosulfate take advantage of both the sulfur and ammonium content by blending with other nitrogen fertilisers such as urea (71). Some foliar-spray fertilisers contain ammonium thiosulfate together with other metal micronutrients (72,73). Ammonium thiosulfate or mixtures with ammonium nitrate can also be used as desiccants and defoliants in crop-bearing plants such as cotton (qv), soybean, alfalfa, rice, and peppers... 

The disadvantages of using urea are that some urea evaporates especially if there is no rain within 4 days of application. It cannot be blended with phosphate nor potassium fertilisers, and it is less suitable on chalky soils. It can cause damage to seedlings. It does not work if the soil is too cold. 

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%. 

Slowly soluble phosphate glasses are used as micronutrient carriers in agriculture. Essential trace elements are incorporated in the glass (Table 12.26) which can then be blended with a macronutrient fertiliser (Section 12.2), or added directly to the soil [15],... 

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. 

Normally, the well-mixed granulated compounds cost more than the equivalent in straights . Bulk blends of straights are usually cheaper. Fertiliser priees have varied considerably in recent years actual costs at ai r time should be substituted in the calculations shown. 

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