Fertilisers Chapter 7

Soil Analysis Ch72 Fertilisers  any material added to soil to supply one or more nutrient elements: organic or inorganic natural or synthetic  necessary to maintain fertility because of intensive cropping  organic fertilisers have the macronutrients – especially the key three N, P and K – but also organic matter which enriches the soil  inorganic fertilisers, which are generally more processed, only provide the macro- and micronutrients

Soil Analysis Ch73 Inorganic  a mixture of salts of the various nutrients  N:P:K grade is an important measure  the %w/w of the three elements (with P expressed as P2O5 and K expressed as K2O)  does not actually contain these forms of P and K  the standard way of reporting their levels eg a fertiliser with a grade of is composed of 10% N, the equivalent of 6% P2O5 and the equivalent of 8% K2O.

Soil Analysis Ch74 Conversion between % Class Exercise 7.1  A fertiliser has a grade of , What are the actual levels of N, P and K?  %N = 14.1, %P = 8.2x0.44 = 3.6, %K = 10.3x0.83 = 8.5 Fertiliser Grade %P %K x 0.44 x 0.83 ÷ 0.44 ÷ 0.83

Soil Analysis Ch75 Exercise 7.2 GeneralSlow ReleaseSoluble Total N N grade Total P P grade Total K K grade

Soil Analysis Ch76 Commercial grade  complete – have the full set of macro- and micronutrients,  trace element mixture – micronutrients only  specific plants – formulations for plants requiring nutrients in different proportions to normal  slow release  soluble – all components are soluble, providing a quick tonic for plants, but one that is readily lost by leaching

Soil Analysis Ch77 Organic fertilisers  Natural material, principally manure, is both: a mulch – a slowly decomposing organic cover over the soil to retain moisture – and a source of nutrients  NPK grade of fresh animal manure is typically around 10:5:10  increased after drying (less water)  different for different animals  addition of organic matter to the topsoil is probably as important in manure fertilising as the provision of elemental nutrients

Soil Analysis Ch78  natural fertiliser is processed before use safety – the risk of disease being spread by animal waste contamination – especially by weed seeds  wood ash is contains a high proportion of potash (K2CO3)  a good source of that element, but is strongly alkaline

Soil Analysis Ch79 Use  overuse by commercial farming activities  pollution of groundwater and surface water through leaching of excess nutrients  lead to algal blooms, toxic algae and eutrophication  timing also important  particularly for nitrogen, which is readily lost if not immediately used  most appropriate time for nitrogen application is the plant moves into its main growth cycle  if the plant is moving towards flowering of fruiting, then nitrogen is the last thing it needs, because it will only encourage leaf growth