FERTILISERS AND HERBICIDES

Fertilisers are mixtures of inorganic salts, the most common ones of which are 

They are designated by three figures expressing, in that order, the percentage of each of the elements N, P and K. For example, a fertiliser 18-22-18 comprises 18% nitrogen, 22% phosphoros, and 12% potassium. An absent element is designated by a zero, so the fertiliser 24-24-0 contains no phosphoros. 

The most commonly used liquids are solutions of nitrate fertilisers (containing between 36 and 40 kg nitrogen per hectolitre), but solutions of superphosphate 14-48-0 (14 kg nitrogen and 48 kg phosphoros per hectolitre) are also used. These solutions are generally slightly acidic (pH between 6 and 7). 

The resistance of aluminium and aluminium alloys depends on the form of the fertiliser and on its composition. 

---

Side effects of fertilisers, pesticides, insecticides, and herbicides... 

A sharp reduction in input use is characteristic of organic farms. Expenditures on these items are consequently also lower. In crop production, the expenditure on fertilisers and sprays is significantly lower. Depending on the enterprise, savings in variable costs of between 30% and 50% are possible. In interpreting these figures, it needs to be remembered that the parameters only include directly applicable fertiliser and plant-protection costs. In addition, the reduction in herbicide use is often accompanied by increased labour and hence higher labour costs. 

Degradable materials also offer new perspectives in agriculture (e.g., the controlled release of fertilisers, insecticides and herbicides)... 

The two most important varieties of pesticides are insecticides and herbicides. There are also other crop-protection agents such as fungicides, acaricides, rodenticides, avicides, bactericides, nemati-cides, molluscides, fumigants, chemo-sterilants, insect repellents and other specialised products. It is usually convenient to group, with these, certain crop-improvement agrochemicals which are not fertilisers. 

In North America, calcium cyanamide is no longer used as fertiliser, but it has limited use in special agricultural appHcations for defoHants, fungicides, herbicides, and as a weed killer. The primary industrial use is as a chemical intermediate for the manufacture of calcium cyanide, hydrogen cyanamide solution, and dicyandiamide. Calcium cyanamide is also used to add nitrogen to steel. 

Most dynamic factors that affect fruit quality are agronomic practices that can be changed by farmers over relatively short time spans. They are mainly related to fertility management and crop protection and other husbandry interventions and inputs such as pesticides, fertilisers, herbicides, thinning agents and so on. The permitted tools for these activities, however, differ greatly between conventional and organic fruit production. The consequences... 

Weed competition for water and nutrients can have similar effects on fruit quality as described above for fertilisation. For example, if weed competition is completely prevented by chemosynthetic herbicides in conventional production, this can lead to excess supply of certain mineral nutrients, in particular nitrogen and potassium, which in turn results in reduced sensory quality and shelf-life (Section 16.2.2). On the other hand, excessive weed competition, in particular, during the pre-bloom phase and the end of the first shoot growth period (Gut and Weibel, 2005), can induce nutrient and/or water deficiency and a risk of quality loss. 

Materials not allowed include highly soluble mineral fertilisers, whether natural or synthetic, such as potassium chloride, urea, Chilean nitrate, single and triple superphosphate and synthetic insecticides, fungicides and all herbicides. 

Polycaprolactones (see also Section 25.11), although available since 1969, have only recently been marketed for biodegradable purposes. Applications include degradable film, tree planting containers and slow-release matrices for pharmaceuticals, pesticides, herbicides and fertilisers. Its rate of biodegradability is said to be less than that of the polylactides. 

Organic EARMING A set of agricultural practices in which no artificial fertilisers, hormones, pesticides or herbicides are used. Organic farming is increasingly popular in developed countries as consumers become more concerned over the potential health hazards of chemical residues in food. Boxes 1.1 and 1.2 (pp. 3-5) provide a more detailed definition. 

---