Efficiency and General Fertiliser Practice

Fertiliser practice has to take into account many variable factors such as (a) the type of plant, (b) the type of soil, (c) the climate - particularly rainfall and (d) the cost. 

Except in the vicinity of phosphate rock deposits, phosphorus is usually present only in topsoil, and below a depth of about a metre its concentration diminishes rapidly. The ploughed layer of soils usually contains about 0.1-1.5% N and 0.02-0.5% P (Table 12.5), but not all of this nitrogen and phosphorus is in a form which is available for plant growth. In unfertilized soils, nearly all the nitrogen and about half the phosphorus are present as organic compounds. These are partially biodegradable into 

The average needs of the three major fertiliser elements per acre, per cropping season, lie within the ranges 50-200 lbs of N, 10-40 lbs of P and 30-150 lbs of K. Assimilation of these macronutrients by the plant is mainly as 

The rate of release of nutrient from the fertiliser is all-important, and ideally this should be tailored to meet the growing requirements of individual plant species. The type of fertiliser, the frequency and method of application may all be crucial. Factors such as temperature, soil pH, rainfall, solubility, size of fertiliser granule, aeration and activity of the soil microorganisms all have to be taken into account in obtaining an optimum of performance.  

All chemical fertilisers operate well below 100% efficiency and a proportion of the N, P and K is always lost and does not appear in the crop. The required concentration of available nitrogen is more easily lost from the soil than that of the other two elements, which can to some extent be stored. Phosphorus is usually considered to be the least mobile of the three fertiliser elements. The chemistry of fertiliser-soil-plant interactions is generally very complex and remains far from being completely understood. 

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