Fertiliser trace elements

Bloremedia.tlon. Cmde oil and refined products are readily biodegradable under aerobic conditions, but they are only incomplete foods siace they lack any significant nitrogen, phosphoms, and essential trace elements. Bioremediation strategies for removing large quantities of hydrocarbon must therefore iaclude the addition of fertilisers to provide these elements la a bioavailable form. 

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. 

Basic slag used to be a popular fertiliser for supplying phosphate, but it also had liming value and contained some trace elements. However, the older steel-making processes are now out-of-date and basic slag is much less freely available. The consequence of this is that soils in Britain are becoming more acidic. 

Many fertilisers for the treatment of deficiencies of trace elements are added to the leaves. In addition, uptake of trace elements from aerial sources through the leaves may have a significant impact on plant contamination, especially of elements such as Fe, Mn, Zn and Cu. Anthropogenic aerosols have been reported to bring about foliar deposition of Pb to a great extent (Streit and Stumm, 1993). Zieve and Peterson (1984) have reported the assimilation of diemethyl selenide through leaves of terrestrial plants. Roberts et al. (1975) found a significant absorption of foliar-applied Zn, Fe, Cd and Mg. 

Eriksson, J. (2001). Concentrations of 61 trace elements in sewage sludge, farmyard manure, mineral fertiliser, precipitation and in oil and crops. 5159, Swedish Environmental Protection Agency, Uppsala, Sweden available on internet at the URL www.naturardsverket.se/pdf/620-6246-8.pdf. 

Mined apatite is a viable source of uranium and toxic cadmium (Tables 2.15 and 4.3). Concern has been expressed that both these elements could enter the food chain via fertilisers made from wet process phosphoric acid. Significant quantities of Pb, Hg and Cu may also be present but concentrations of all trace elements can be very sensitive to exact deposit location [88] (Table 2.16). Prolonged... 

While the presence of most trace metals in phosphatic fertilisers is regarded as beneficial, or at least harmless, concern has been expressed over the trace cadmium content. Most trace elements in commercial fertilisers do not greatly add to the levels already present in soils, but the amount of Cd does, however, represent a significant increase [38] (Table 4.3). Cadmium is considerably more toxic to humans than it is to plant life, and there arises just the possibility that in another century or so, it may have built up and become present in the food chain at harmful levels. 

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],... 

The main constituents for compound fertihsers used in the United Kingdom are urea, mono and diammonium phosphate and potassium chloride. These compound fertilisers, or compounds, supply two or three of the major plant foods (nitrogen, phosphoms and potassium). Other plant foods, e.g. trace elements, as well as pesticides, can also be added, although this is not commonly done now. The exception to this is sulphur which is increasingly being offered as part of compound fertilisers to overcome the deficiencies in certain parts of the country. 

Prior to the agricultural and industrial revolutions, the main fertilisers applied to the land were animal products which had been derived from it, such as blood and bone meal, farmyard manure and human faeces although seaweed was also applied in coastal areas. A large fraction of the trace elements removed from the soil was therefore returned and the rate of depletion was therefore relatively slow. The system of agricultural production was therefore, to a large extent, self-regenerating, in that both major and minor nutrients were returned to the land in balanced proportions. Although the problem of dispersion of non-essential elements did not exist, soil fertility was sustained by this system at a low level by modem standards. 

While the trace-element content of guano and, to a lesser extent, of mined mineral salts, could make some contribution to the nutrient requirements of crops, these materials are no longer adequately available. We have now become largely dependent on highly purified compound fertilisers containing only nitrogen, phosphorus and potassium as nutrients, so that the rate of depletion of essential trace elements has been greatly accelerated. The natural cycle... 

Comprehensive information on the trace element content of fertilisers has been published by Swaine [113] and it is evident from the levels cited that losses of trace elements from soils under cultivation are not normally made good by the application of fertilisers and lime. There will be, however, some contribution from these sources, and traces of an element present in an available form may be important when crops are grown in soils low in this element. 

Basic slag is commonly thought to provide useful supplies of essential trace elements in addition to its value as a phosphatic fertiliser, but figures published by Swaine for the conq[)osition of this material do not really bear this out. 

Any fertiliser containing 100 ppm of a trace element, applied at a rate of 100 kg per hectare, will produce an increase in trace-element content in the surface horizon of the soil (0-20 cm) of 0.005 ppm. On the basis of figures quoted by Swaine [113], basic slag normally contains less than 40 ppm boron,... 

Although much larger applications of lime, than of fertilisers, are made as routine to agricultural land, the levels of essential trace elements in limestone are generally so low that liming materials do not seem to make any great contribution either, to the reserves in the soil. 

The fact that the normal fertiliser and liming program makes no provision for the replacement of losses of essential trace elements from the soil has led to a situation where commercial interests are able to market shot-gun mixtures to farmers with problems, sometimes at exhorbitant prices. Extravagant claims have been made for some of these products in order to justify their widespread sale. Many farmers are now acquainted with the fact that dramatic improvements in productivity of crops or stock are possible when a particular trace-element deficiency is remedied by supplying the appropriate element, and salesmen are sometimes assisted in their efforts to sell shot-gun mixtures by the mystique now associated with the term trace elements. It is unlikely, however, that on most farms, the application of a mixture containing all the essential trace elements would have any significant effect on crop yields in the short term. 

Fluorine is another potentially-toxic trace element which is dispersed by atmospheric pollution and it has long been recognised that damage to plants occurs and that there is a hazard to man and farm stock, in the vicinity of industrial plants processing fluoride-containing minerals. Such plants include factories for the production of aluminium, superphosphates and compound fertilisers based on the liberation of phosphoric acid from rock phosphate. In October 1976, ten cows had to be destroyed on two farms in the vicinity of the British Aluminium Company s aluminium smelter at Invergorden in the north of Scotland, and problems of fluoride toxicity have been commonly associated elsewhere with the production of aluminium. 

The levels of trace elements found in the majority of sludges are so high that their use as fertiliser must inevitably lead to contamination of the soil One cannot, therefore, generalise about the suitability of sludge as a fertiliser, since each batch produced must be judged on the basis of its trace-element composition, and this may vary widely even from a single disposal plant. 

Fertiliser treatments can affect the trace-element uptake of plants and reductions in manganese and cobalt uptake have been observed following nitrogen applications. These effects and the influence of physical soil factors on availability have been discussed by Reith [114] and Reith and Mitchell [,303]. 

D.J, Swaine, The Trace-Element Content of Fertilisers, Tech. Comm. No.52,... 

Trace-Element Uptake by Plants, Proc. IVth Intern. Colloq. on Plant Analysis and Fertiliser Problems, 1964, pp. 241-54. 

Conversely, an excess soil P may effect the uptake of some micronutrient elements. A high P content can induce a zinc deficiency in the plant, even if sufficient zinc is present in the soil. On the other hand, the uptake of manganese from alkaline manganese-deficient soils can be increased by the presence of phosphatic fertilisers. There is also some evidence that excessive and prolonged buildup of phosphatic fertilisers in the soil might lead to toxic effects due to the trace quantities of certain metals (e.g. Cd above) in the fertilisers [38,59-61]. 

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. 

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