Different crops have different nutritional requirements from soil. By growing different crops on a field from year to year can prevent the soil to be short of one particular type of mineral due to exhaustive uptake by the same type of crops over years.
Long rooted plants can be followed by short rooted plants so that minerals are withdrawn from different levels of soil.
(b)Including leguminous plants in crop rotation
Leguminous plants (e.g. clover, pea, beans). They have a mutualistic relationship with the nitrogen-fixing bacteria contained inside their root nodules. The bacteria can change the atmospheric nitrogen into nitrogenous compounds which are then used by the legumes to make amino acids and proteins. When the residues of these leguminous plants are ploughed in, they will get decomposed and increase the soil nitrogen content.
…
