VALUE OF ROTATION.

New Zealand Herald, Volume LXI, Issue 18601, 8 January 1924, Page 10

VALUE OF ROTATION.

A result of cultivation as tin/ ex. haustion of the soil,, which is readily seen in fie case of sick soils or sick plants. While the same crop may be sown on the same soil for some seasons without a marked decrease in the yield this will sooner or later show itself unless extraordinary efforts, which are too expensive, are made to prevent this. . The same crop grown successively tends to exhaust a soil. This is because difficult crops require constituents in different proportions, and while wheat may draw its .nourishment from deeper layers of the soil, leaving the upper layers untouched, another, such, as barley, will draw its food from the shallow layers. A continuance of either is exhausting, but an alteration of the area from which food is drawn by growing of crops differing in their root systems minimises the tendency to exhaustion. The whole area is then drawn upon equally. All this tends to show the necessity of change of crops on the same ground anannually. What one crop ... demands , from the soil differs from the requirements of another. A change of crop helps to rid the soil of a disease which has flourished by growing the same crop continuously. Another reason why the same soil is bad for the same crop grown year after year is that weeds are encouraged thereby. . Growing wheat continuously does not enable the thorough cleaning of the soil that takes place when roots are grown to be effected. Many advantages accrue from rotation of crops. Not the least is tho increased yield and vigour of crops. A crop which has lost vigour, growing on exhausted soil, is more exposed to disease and less able to resist it. Most insect pests live only on a particular food plant or certain allied ones. Fungoid pests are equally restricted. A change of crop deprives them of their plant food, and so helps to exterminate them. There is also more economy of labour in the sowing, manuring, and cleaning of land under a rotation both as regards horse labour and manual labour. Manure is also used more effectively. The alternation of difficult crops preserves a balance, as one crop requires more of one kind and another more of another. The preparation of the soil for cultivation of crops is also simplified. -