Crops that are grown for their grain, the “seed”, such as most of the cereals and oilseeds
and many of the legumes, are normally harvested when their seed is mature. A mature
seed is one that has developed sufficiently so that it would germinate if it were in the
right conditions of temperature, moisture and air.
Many other crops, including most fruits and vegetables, are harvested before they
mature. Many of the leguminous crops are also harvested before maturity, when the
fresh green pods or grains are taken and eaten as a vegetable.
The number of days from planting the seed of a crop until the plant is mature and
ready for harvest is often called the growth period of that crop.
Some crops such as oats, rye, sesame and vetch (grass pea) Lathyrus sativus should
be harvested before the plant is fully mature—at a point when the seed is mature, but
still has a relatively high moisture content. The reason is that with these crops the seed-
heads or pods dehisce or shatter readily ie they open and so allow their seed to fall to
the ground and become lost. The seed then has to be dried before it can be stored.
In agriculture and horticulture the yield of a crop is the term used to describe the amount
of food produced per unit area. If 1000 kg of sorghum grain is harvested from one
hectare of land, the yield is 1000 kg/ha.
Yield is normally expressed in kilograms per hectare (kg/ha) or tonne per hectare
(MT/ha or tonne/ha).
Average Yield
The yields of food crops depend on a whole range of factors and so it can be very
misleading to quote the “average yield” of any particular crop. Even the same variety of
a crop can produce widely differing yields if they are grown under different conditions
of soil type, climate etc. The Ministry of Agriculture or its equivalent can often provide
information about the average yields of the crops which are grown in their area, but the
information should be viewed with caution as it is often inaccurate, for reasons
explained above.
Mixed (or multiple) cropping systems, very commonly found in poorer parts of the
world, can also confuse estimates of yields per unit area. It should be made clear if any
average yield figures apply to the crop when grown alone (in pure stand) or when it is
mixed with others.
The average yields of most of the important food crops are quoted in Section 2,
“Description and Characteristics of the Main Food Crops”.
76 TONY WINCH
I The Harvest
“ ”
a Maturity
1Ib. Yield