Principles of Crop Rotation
Planning a crop rotation, and adapting it when necessary, requires paying attention to a
number of factors, including the following:
- legumes like alkaline soils or plenty of lime in more acid conditions, while Irish
potatoes prefer more acidic soils; - Irish potatoes like a lot of manure, while other root crops such as carrots do not
because manure can often cause their roots to become forked ie they split; - the Brassica family also like lime, but only after it has been in the soil for about a
year; some crops should not be grown on the same land two years in succession,
mainly to avoid the build-up of diseases. Ideally some years should elapse between,
linseed (5–6);- if lime is put on the land for a crop such as soybeans, then the next year’s crop can
be one which likes some but not a lot of lime, such as maize or tobacco. The third
year can be a crop which likes only a little lime, such as cereals or Irish potatoes; - in low rainfall areas more drought resistant crops such as millet may be the only
ones to survive following a crop that takes a lot of water from the soil, such as
lucerne (alfalfa); - if grassland is ploughed in, even if it has only been established for a year or so, this
will increase the soil organic matter and will also improve the tilth of soil which
may have become compacted by heavy rain, machinery, trampling by animals etc.; - the type of soil—some can successfully grow crops of sorghum, barley and so on
for many years, while other soils would rapidly lose fertility or become infested
with diseases and/or pests, and so need frequent break crops of legumes, root crops
etc.; - the deep root penetration of some crops such as lucerne and clover brings up
nutrients from deep in the soil and also helps to increase soil aeration which can be
highly beneficial to the following crop; - market prices often have a greater influence on the choice of crop which is grown
than the proper use of land; - cultural and traditional beliefs, the need for food security and the availability of
seed or planting material are some of the other factors which play a part in the use,
or abuse, of crop rotations as an invaluable tool in the food producer’s armoury.
Mixed, or multiple, cropping is the name given to farming systems where more than one
crop is grown on the same land in a year. The most common types of mixed cropping
systems are various combinations of intercropping, but there is another important type
known as double (multiple) cropping in which either:
- successive but different (fast growing) crops are grown in the same field in the
same season, or
for example (with number of years in brackets)—peas (3–5), sunflowers (4) and