Application of fertilisers

There is no difference in plant growth following the application of fertiliser in solution, suspended or solid form. The benefit of fluid fertilisers seems to be that they can be delivered more quickly and accmately to the plants and urea in fluid form is not as volatile as the solid product, particularly important in drying conditions. 

Broadcast distributors using various mechanisms such as  

Combine drills. Fertiliser and seed (e.g. cereals) from separate hoppers are fed down the same or an adjoining spout. A star-wheel feed mechanism is normally used for the fertiliser and this usually produces a dollop effect along the rows. In soils low in phosphate and potash, this method of placement of the fertiliser is much more efficient than broadcasting and can require less fertiliser to be used per hectare, e.g. P and K in potatoes. It is known as combine drilling and is sometimes referred to as contact placement . Because of possible scorch, combine drilling should only be used for cereal crops. 

Placement drills. These machines can place the fertiliser in bands 5-7 cm to the side and 3-5 cm below the row of seeds. It is more efficient than broadcasting for crops such as peas and sugar beet. Other types of placement drills attached 

Broadcast from aircraft. Rarely used except in inaccessible hill land and forests. Usually done by helicopter. Highly concentrated fertilisers should be used, e.g. urea. 

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Ammonium in aerosols originates from the neutralisation of sulphuric and nitric acid by ammonia. Ammonia is emitted by different sources, most notably animal manure, traffic and application of fertiliser. In general, emissions are for the largest part (80-95%) associated with agricultural activities [19]. Erisman et al. [20] estimated the natural emissions at about 10% of the total emissions in Europe. This percentage includes contributions from wild animals and wetlands. We assume a similar percentage for ammonium in north-western Europe. 

These soils are prone to nutriertt loss and are very responsive to application of fertilisers. 

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. 

Losses of major elements are normally made good by the application of fertilisers and lime, but most modem fertilisers contain little or no sulfur,... 

In agricultural ecosystems, the P cycle is more open than in undisturbed ecosystems, because some losses occur by the removal of agricultural products and in some situations by surface runoff and erosion. Applications of fertiliser are needed to compensate for these losses, as well as to raise the level of production above native levels. Where grazing animals are present, unevenly distributed returns of P through dung and, to a small extent, urine also occur. Consequently, in managed ecosystems the natural P cycle is modified by these additional factors, so that the importance of P mineralisation for plant nutrition is more difficult to assess. This is why... 

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. 

One of the problems is that the phosphate fertiliser allowed by the organic regulations is rock phosphate, and research in Austria has shown (Lindenthal, et al., 2000) that the application of rock phosphate had virtually no effect on subsequent crop yields. 

Normal agricultural practices generally cause an enrichment of heavy metals in soil, particularly Zn, Cu and Cd, due to the application of manure or its derivatives, compost or sludge and inorganic fertilisers and other human activities such as... 

The nitrogen content of the various crop species and their parts exhibits a wide range of variation from 0.2- 4% (Table 5.9). It depends not only on the species and on the harvest time, but also on the fertilisation rate. This is known for conventional crops (Mollers 2000) and was confirmed for energy crops too (Scholz et al. 1999, 2004a). Depending on the species, the application of e.g. 150 kg N ha-1 causes an average absolute increase in the N content by 0.1-0.3%. 

Although the nutrient content of wastes makes them attractive as fertilisers, the application of many industrial wastes and sewage is constrained by the presence of heavy metals, hazardous organic chemicals, salts and extreme pH values. 

Application of sludge on agricultural soils could result in these organics entering the food chain. As many of these compounds are toxic to humans or animals, their presence could be a constraint for the use of sludges as fertilisers. Some food companies have set soil limits above which crops grown on such contaminated soils are rejected [11] Aldrin/Dieldrin, 0.1 DDT, 0.75 and Diuron, 0.3mg/kg soil. 

Fillery IRP, Simpson JR, De Datta SK. 1986. Contribution of ammonia volatilization to total nitrogen loss after applications of urea to wetland rice fields. Fertiliser Research 8 193-202. 

It pursues a number of aims, such as the production of products which contain no chemical residues, the development of environmentally sensitive production methods which avoid the use of artificial chemical pesticides and fertilisers, and the application of production techniques that restore and maintain soil fertility. 

N2O contributes to the greenhouse effect with 4% (Schonwiese 1995). N2O emissions from agriculture come from mineral and organic N-fertilisers and from leguminous crops. The emission levels depend on the kind of fertiliser and on the application technique. The N2O emission factors for the most frequently applied forms of mineral N-fertilisers are < 0.5%, for organic manure 1.0 - 1.8% and for N from legumes, about 1% of the fixation rate. 

As the application of mineral N-fertilisers is not permitted in organic farming systems, the following factors concerning the situation in organic animal husbandry (with regard to the emission of NH3) have to be noted (Oomen and van Veluw 1994 Unwin et al. 1995 Vries et al. 1997) ... 

Soil surface balance measures the differences between the input or application of nutrients entering the soil (e.g. mineral fertilisers or organic manure) and the output or withdrawal of nutrients from harvested and fodder crops. Farm gate balances measure the nutrient input on the basis of the nutrient contents of purchased material (e.g. concentrates, fertilisers, fodder, livestock, biological N-fixation) and farm sales such as meat, milk, fodder, cereals (OECD 1997). 

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