Crop rotation is the practice of growing a series of dissimilar types of crops in the same space in sequential seasons to avoid the build-up of pathogens and pests that often occurs when one species is continuously cropped. Crop rotation also seeks to balance the fertility demands of various crops to avoid excessive depletion of soil nutrients.

For the purpose of planning crop rotation, plants are grouped by family (because they make similar demands and have similar susceptibilities).

Here are some examples of frequently grown crops, by plant family Leguminosae (NF) nitrogen fixers:


The humble broad bean might help to prevent bowel cancer - the second most common cause of deaths from cancer in the UK, scientists have claimed.

Researchers from Hammersmith Hospital and the Imperial College of Science, Technology, and Medicine, London, assessed the effects of dietary lectins on the behaviour of cancer cells in the colon.

Lectins are proteins found in many plant foods, including broad beans.

They attach themselves to carbohydrate molecules, which are then absorbed by the cells lining the bowel during digestion.

The findings, published in the medical journal Gut, showed that broad bean and mushroom lectins were able to halt or even reverse the cancer process.

A normal healthy cell is said to be well differentiated, meaning that its characteristic features and structures are intact, enabling it to function properly.

Loss of differentiation is a hallmark of cancer cells.

Cancer halted

The broad bean and mushroom lectins were able to increase the differentiation of cancer cells, indicating that the cancer process was either being halted or reversed.

The lectins also seemed to inhibit cell multiplication, another hallmark of cancer cells.

The way in which lectins attach themselves to the carbohydrate molecules may be particularly important in the development of cancer, say the authors, because these molecules are very active in the processes that turn on and switch off cell growth.

It is the mis-firing of this process that is believed to cause cancer.

Lead researcher Professor John Calam said: "It is well known that diets high in fruits and vegetables protect against many types of cancer, including bowel cancer.

"The lectin effect may be one of the reasons why."