Soil nitrogen supply

The new Defra nitrogen recommendations continue to use Soil Nitrogen Supply (SNS) as their basis but the system has been fully revised with clearer definitions of soil type and revised index tables. Defra defines SNS as the amount of nitrogen (kg N/ha) in the soil (apart from that applied for the crop in manufactured fertilisers and manures) that is available for uptake by the crop throughout its entire life, taking accoimt of nitrogen losses . It is calculated using the equation ... 

Table 4.4 Defra soil nitrogen supply index system (SNS)...

Soil Nitrogen Supply Index - see Defra RB209. 

Less nitrogen is needed in wetter areas, although exactly how much is used wiU depend on the soil nitrogen supply status. More phosphate may be needed on heavier soils, but this will a in depend on the soil phosphate index if the fertiliser is placed 5-10 cm below the seed, the phosphate can be reduced. Potash is important, but savings can be made by using organic manures. As with fodder... 

Soil Nitrogen Supply Index - see Defra RB209. Where FYM and slurry have been used the above reconunendations should be reduced to take account of the available nutrients so supplied. These recommendations have been based on Defra RB209 (8th edition) issued in June 2010. 

Table 20.3 Soil Nitrogen Supply (SNS) status classes in grassland (from Defra, 2010)...

Figure 1.4 also shows two other reactions. In reaction 2, ammonia reacts with water to form ammonium hydroxide. Reaction 3 shows that ammonia can also be oxidized to form nitric acid from which all forms of nitrates can be produced. All three forms of nitrogen (ammonia, ammonium hydroxide, and nitrates in various forms) are commonly found in soil and can be added to soil to supply nitrogen to plants (see also Figure 6.5). This process thus opened up an inexpensive method of producing nitrogen compounds that would be used as fertilizers.

Casals, P., J. Romanya, J. Cortina, J. Fons, M. Bode, and V. R. Vallejo. 1995. Nitrogen supply rate in Scots pine (Pinus sylvestris) forests of contrasting slope and aspect. Plant and Soil 169 67-73. 

The nitrogen supplies on land consist of the assimilable nitrogen in the soil VS2 0.19-104tkm-2, in plants (12 1091), and living organisms (0.2 1091). A diversity of nitrogen fluxes is formed here of the processes of nitrification, denitrification, ammonification, fixation, and river run-off. The intensities of these fluxes depend on climatic conditions, temperature regime, moisture, as well as the chemical and physical properties of soil. Many qualitative and quantitative characteristics of these dependences have been described in the literature (Hellebrandt et al., 2003). Let us consider some of them. 

Chaignon, V., Bedin, F., and Hinsinger, P. (2002a). Copper bioavailability and rhizosphere pH changes as affected by nitrogen supply for tomato and oilseed rape cropped on an acidic and a calcareous soil. Plant Soil 243, 219-228. 

Deficiencies of soils to supply the essential elements are more obvious in plants than in animals. The nitrogen content of most soils is low enough that plants benefit from added N. In many soils, plants, especially food crops, also grow better with added P, K, and S. Because the response differs among plant species, fertilization can change the distribution of plant species. Since we usually define the untouched plant community as the ideal state, species changes are considered detrimental. 

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