Fertiliser requirements

To make useful determinations of the fertility of soils or of the fertiliser requirements for crops, a laboratory must use test methods that are suitable for the specific types of soils it receives. It will have been shown that the test results correlate reasonably well with the... 

Lime and fertiliser requirements. Some soil types have different abilities both to hold and release nntrients. Most clay minerals have a negative charge which attracts positively charged ions such as potassium, magnesium and calcium. This is called the cation exchange capacity. The presence of these charged sites affects the availability of nutrients. Sand and silt are relatively inert. Different soil textures with the same level of acidity have different recormnendations for the application of lime. This is due to differences in the cation exchange capacity of the soil. 

Others would extend the fertiliser concept to the simultaneous addition of readily biodegradable substrates along with the fertiliser nutrients to stimulate the growth of contaminant-degrading organisms most rapidly, and to aid in the rapid utilisation of the fertiliser nutrients before they might be leached from the contaminated area. The specific requirements for the most efficacious substrates is an area of current research. 

By housing cattle overwinter and composting the farmyard manure, the organic farmer has ready access to a balanced fertiliser that can be spread where most required. The grazing animal does not actually import fertility onto the farm but it does recycle nutrients where it grazes and provides a source of manure when housed. This is as true of sheep, pigs and poultry as of cattle. The only problem with outdoor pigs is that they tend to rip up pastures. 

Related to chemical pollution - referring to all kind of contamination (mineral and organic) - there is a clear distinction between point-source pollution and diffuse pollution. It appears that it is easier to take measures for point-source pollution, for instance, the improvement of the wastewater treatment plants, even if the treatments for specific compounds (pesticides, emerging compounds, etc.) still need further research. Measures for diffuse pollution can be more complex because some of them require real political decisions, for instance to interfere on agricultural practices to reduce inorganic and organic fertilisers. 

Long-term field trials in England have shown that N efficiency of cattle slurry applications declined once the application rate exceeded pasture plant requirements [7], The cattle slurry was reported to be 90% as efficient as ammonium nitrate fertiliser when applied at 300kg N/ha compared with 63% efficient at 600kg N/ha and that the efficiency varied with season of application, being most effective in spring. 

In most of today s ethanol plants for the conversion of wheat, rye and corn, the required thermal energy is provided by natural gas, heavy fuel oil or coal. The protein-rich by-products of ethanol plants are referred to as dried distillers grains with solubles , abbreviated as DDGS, and are mostly used for animal fodder. Alternatively, they can be converted to biogas for heat and electricity production. The resulting residue can then be used as fertiliser (see Table 7.16). 

At the other end of the spectrum, many very fine powders are frequently to difficult handle, and may also give rise to hazardous dust clouds when they are transported. It may therefore be necessary to increase the particle size. Examples of size enlargement processes include granulation for the preparation of fertilisers, and compaction using compressive forces to form the tablets required for the administration of pharmaceuticals. 

Much of the behaviour of humans and society as a whole is designed to provide an opportunity for a sperm and an ovum to meet in the uterus. However, sexual reproduction is not the only means of reproduction asexual reproduction occurs frequently in the animal kingdom and in many tissues in order to increase the number of cells during growth or to maintain the number due to cell death. The question arises, therefore, why sexual reproduction has arisen at all since it is very expensive in the use of resources for example, in the process of selecting a suitable mate, and in the requirement for males, whose only function in some species is fertilisation of the females, yet they use resources that could be used by the females and by the offspring. Perhaps because of this, a few species of vertebrates (e.g. some lizards) have retained the option for asexual reproduction. This process is known as parthenogenesis. Mammals, however, have lost this option. This... 

The spermatozoon consists of a head, a midpiece and a tail or flagellum. The head contains the nucleus and a vesicle known as the acrosome (Figure 19.4). It contains hydrolytic enzymes that are required during fertilisation of the ovum. 

Recent developments to the hydrothermal process include improvements in yield and reaction rate and in overcoming the difficulty associated with the coproduct salt. One method of overcoming the co-product problem is to use magnesium nitrate instead of chloride, with the ammonium nitrate being utiHsed for fertiliser production [102-104]. At least one plant based on this concept is now in commercial production. While a considerable advance on the initial chloride process, the nitrate route does require close integration with a fertiliser process and thus lacks flexibility. An alternative approach being developed is to recycle the ammonium salt co-product (nitrate or chloride) and use it to leach magnesium oxide, a potentially inexpensive raw material [103]. 

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