SOIL PRODUCTIVITY.

New Zealand Herald, Volume LXIV, Issue 19627, 4 May 1927, Page 18

SOIL PRODUCTIVITY.

According to the Bureau of Soils of the United States Department of Agriculture, the United States will have to depend upon the cultivation of the soil for about one-third of its combined wheat, maize, and oats produced, upon crop rotation for another third, and upon the use of manures and commercial fertilizers for the other third. It is logical, states the bureau, that cultivation aids both rotation and fertilisation, that rotation aids in rendering fertilisers more effective, and that fertilisers increase the value of rotation. Recent experiments, however, bring out the fact that rotation and the use of fertilisers, when practised together, may interact to the extent that thei l " conjoint effects, as measured in terms of crop increases, may be not only equal to but greater than the sum of their separate effects. The average yield of maize obtained without fertilisers and rotation in these particular experiments was 23.4 bushels per acre. The gain due to using fertilisers and lime wan 9.2 bushels per acre, and the gain due to rotation alone was 27.8 bushels, or practically three time? that, obtained from the fertilizers and lime. The total increase effected Tjy "conjoining rotation and the use of fertilisers and lime was 9.2 bushels per 7.2 bushels greater than the sum of their separate increases. Other experiments conducted hv the bureau have corroborated these results, which emphasise the importance of recognising all three factors in striving lor permanent soil productivity.