Sometimes called change crops, for reasons explained below.
In many parts of the world food growers have a marked preference for one crop
more than others; this may be a cereal, often maize or sorghum, or a root crop such as
cassava or sweet potato, or even sometimes an oilseed crop or a vegetable.
If one of these crops is grown continually on the same land for a number of years,
this farming practice is known as continuous cropping or monoculture. The danger with
this practice is that certain kinds of weeds, diseases and insect pests tend to build up,
and certain soil nutrients also become depleted. As a result, crop yields tend to diminish
after a few years.
Food producers can respond to these falling yields in different ways. They may
accept the situation fatalistically, or they could launch a chemical attack on the weeds,
diseases or insects, or they could introduce a break crop—in other words another type of
crop. There are a number of advantages to break crops:
- diseases which are carried over from one season to another, either in the soil or in
crop residues, are less able or unable to survive and consequently damage
subsequent crops; - insect pests are similarly often, but not always, reduced in numbers;
- the soil is depleted of a different proportion of soil nutrients, some of which may
have become exhausted under a monoculture—legumes would contribute nitrogen,
for example. A break crop may even sometimes increase the soil’s organic matter
content; - there is no expense, trouble nor possible danger of applying chemicals.
The best type of break crops are those which are equally useful as the crop which is
normally grown. The break crop should provide the same amount or more of food or
income. It may also have useful by-products (eg stalks/stems for building or fodder)
which are not produced by the normally grown crop, and it should not have an
excessively long growth period ie it should “fit in” with the other crops on the farm.
There are three main types of break crop:
- Seed Crops—peas, beans and oilseed crops that are planted every few years
between a cereal monoculture can be very beneficial. Even oats or maize can be
used as break crops to reduce disease build-up in other cereal crops. - Root and Forage Crops—these also usually help to slow the build-up of weeds,
diseases and pests when they are grown after a cereal monoculture. - Grassland—this can be a very valuable longer term (2–10 years) break crop,
especially if it is well used, for grazing, hay or silage, and if it can be easily
reconverted back to an arable crop when necessary. Efficient ploughing and even
herbicides may be necessary to successfully change grassland back to arable
cropland.