Pioneer crops are normally associated with grassland or with recently cultivated “new”
land. When old grassland has become exhausted or needs renewing for some reason, it
is ploughed up and a pioneer crop is then often planted. A typical pioneer crop in
temperate zones is a mixture of Italian ryegrass, rape and turnips.
Pioneer crops are normally fertilised and/or grazed heavily by animals so as to
accumulate dung and urine in the soil, and then ploughed under. This process may be
repeated if the old grassland or “new” land is in a very low state of fertility.
A crop which is planted densely (ie at a very high plant population) and which grows
vigorously to occupy most of the growing space is known as a smother crop. The
purpose of smother crops is to retard or smother the growth of weeds; if legumes are
used then they will also increase the soil nitrogen content as well as crowding out the
weeds.
Smother crops (as well as trap crops and cover crops) are often ploughed under after
they have served their function, in which case they also serve the purpose of providing
green manure.
Examples: alfalfa, foxtail (Italian) millet, buckwheat, rye, sorghum and Sudan grass.
Some plants prefer shady places to grow in, other plants like to be in the full sun. The
There are many and varied ways in which taller, sun loving plants can be planted so
as to provide shade and protection for smaller shade loving ones. In addition to
providing shade the sun plants also usually provide some form of additional protection,
from wind, animals and so on. Permanent shade trees for example - which are often
planted to provide shade for coffee or cocoa - also provide a range of advantages: their
branches even out the temperature fluctuations between day and night and produce a
more favourable microclimate, they extend the life of the shade plants below them, and
they reduce dieback and biennial bearing habit.
Shade crops can also reduce evaporation and transpiration, and damage from hail
and weeds; the leaf mulch is taken more efficiently into the soil, and gives longer
protective cover for the soil; their root systems may assist drainage and aeration; and
they may provide firewood, timber, honey and other useful products. Not bad.
On the other hand great care should be taken in planning or managing shade trees
since they can also harm crops by removing excessive water and nutrients. They need
careful management so that there is a well-matched balance between the species chosen
for each purpose.
Trees are not the only species grown to provide shade; annual plants are also
frequently used as shade crops. Examples in temperate climates, where shade crops play
64 TONY WINCH
difference between the two is discussed in 1Eg. “Shade Plants / Sun Plants”, page 40.