climates, especially those with distinct rainy and dry seasons. If soils samples are taken
at this time, misleadingly high levels of soil nitrogen may be recorded, leading to less
than optimum applications of nitrogen fertiliser at planting time.
In addition, a small amount of nitrogen, about 2–4 kg/ha, can often be added to the
soil by rainfall, as oxides of nitrogen created by lightning (1Ae, page 6).
Plant Food (Nutrient) Requirement of Food Crops
The amount of food required for each crop varies widely, and also depends on the soil
type (including any inherent deficiencies in major or minor deficiencies), the yield
target, the season and the previous cropping and fertiliser use.
A few examples are listed below, but only for illustrative purposes—professional
advice should always be taken before the amount and type of fertiliser is used or
recommended.
Crop Kg/ha
N P K
Winter wheat
Barley (feeding)
Maize
Sorghum
Legumes
Irish Potatoes
Carrots120 50 50
100 50 50
120 45 45
(^85 30 30)
0 50 50
220 250 300
60 125 95
Split Dressing
Winter sown crops in temperate climates are not normally given much nitrogen at
planting time because most of it would be leached before it could be used by the crop.
Instead, the fertiliser is split
planting time, and nitrogen in the spring.
A split dressing is also often advisable for a number of crops in other climatic
regions. With maize for example some fertiliser is often applied before or during
planting, some a few weeks later, and the last application just before pollination.
Storing Fertiliser
Fertiliser should be stored as cool and dry as possible. If it is in plastic bags, these
should be stacked neatly and flat to minimise rips in the bags. Take care to keep water
well away; some fertilisers are also a moderate fire risk.
For the benefit of illiterate people involved, the bags should be marked with a clear
design to indicate their potential danger.
Fertiliser is sold by the manufacturers in various forms: “Big Bags” of half or one
tonne (MT), in bulk, in liquid or gas form, or in 50 kg plastic bags. At the village market
level it is often sold in very small quantities, sometimes for prices well above its actual
economic value (see above).
-dressed— for example, phosphate and potash is applied at