More modern non-mercury dressings tend to be more specific in their action, so the
trend nowadays is to use a cocktail of various dressings. Unfortunately the non-mercury
dressings tend to be more expensive.
Insecticides
Insecticidal seed dressings are more recent than the fungicidal dressings and only
became widely used following the development of the organochlorines in the 1940s.
The cyclodienes (Aldrin, Dieldrin, Heptachlor, Chlordane and Endrin) as well as DDT
have been withdrawn from use in most countries for environmental and health reasons.
Vernalisation is the subjection of plants at the seedling stage to a period of cold
conditions, which triggers mechanisms in the plant which lead to flowering.
Some varieties of some plant species such as winter wheat and barley will fail to
flower if they are planted in the warm weather in the spring. These varieties need to be
vernalised by a cold winter period before they will produce flowers, and consequently
seed. Varieties that display this characteristic are known as winter varieties and are
planted in temperate regions in the autumn. Normally, temperatures of 0–8°C for a
period of one or more weeks are necessary to stimulate flowering.
By contrast, spring varieties require no cold period, or vernalisation. They are
planted in the spring, and flower in the summer of the same year. Some varieties of
cereals (including triticale) are said to be facultative or intermediate; these varieties can
be planted either in autumn/early winter if temperatures are not too low, or in spring if
the growing season is long enough.
Vernalisation can be achieved artificially, by keeping the seed moist and between
1 °C and 2°C for up to eight weeks, or even longer for some species.
1G. CROPS
If it is possible to construct an accurate cropping calendar of the area where you are
studying the food production systems then you are a long way towards understanding
the agricultural crop situation in that area.
A cropping calendar, or Crop Year Table, is simply an easily understandable display
of the crops grown in any particular location. It shows very clearly which crops are
grown, and during which months they are planted, cultivated and harvested.
Other information such as average rainfall, temperature, etc. can also be included on
the calendar.
It is also possible to indicate on a cropping calendar which crops are the most
important, from any particular point of view (area cultivated, economic value,
nutritional value, harvest yield etc.). This can be done by not only listing the crops in