CROP ROTATION.

Putaruru Press, Volume V, Issue 176, 17 March 1927, Page 6

CROP ROTATION.

EFFECT OF SOIL BACTERIA. Interesting Experiments. . That a change of crop, as in a rotation, is of advantage id ay be regarded as an agricultural truism, and the reason is considered to be that crop requirements for plant food are not the same, so that whereas one crop may make the greatest demand on the nitrogen in the soil, the succeeding crop will require more phosphate and potash. Thus, a cereal crop will take most nitrogen, while the root crop calls for more phosphate, and there is. of course, the further advantage rhat the cultivation of the land for the root crop helps to clear the land of weeds. Now, however, it is claimed that the change of crop stimulates bacterial life, and from this point of view the system of different rotations will have to be considered more carefully. A series of experiments have been made, and are being continued in America to throw light on the problem, and, meantime, the following conclusions have been arrived at:— 1. The rotation of crops caused the development of greater numbers of organisms in the soil, and of greater ammonifying, nitrifying, and nitrogen-fix-power by the soil than continuous cropx3ing either to corn or to clover. 2. Greater numbers of organisms, and greater ammonifying, nitrifying, and nitrogen-fixing powers, were found in a soil under a three-year rotation of corn oats, and clover, than in a soil under a two-year rotation with clover, cow-peas or oats turned under as green manure. 3/ The use of a green manure in a two-year rotation did not always increase the number of bacteria or the ammonifying, nitrifying, tyr nitrogen-fix-ing power of the soil, and it is suggested that the explanation may be sought in tae moisture factor or it may be found in the introduction of such large amounts of organic matter. 4. There was an indication that the crop present on the soil was of more importance from the bacterial standpoint than the previous cropping of the soil. 5. The ammonification of dried blood and of cottonseed meal did not always run parallel. 6. The nitrification of dried blood and of ammonium sulphate proceeded almost parallel.