A MANURING PROBLEM.

Waipa Post, Volume XIX, Issue 1104, 11 June 1921, Page 6

A MANURING PROBLEM.

♦ DO PHOSPHATES SINK? IMPORTANT TESTS. A series of experiments was instituted in California with a view to ascertain to what depth phosphoric acid, added in the form of phosphoric fertiliser was carried by the rain into the various soils. The experiments were made primarily for the purpose of finding out whther these manures, when added in the orchard, are carried down to the roots of the trees. According to Professor Loughbridge, who conducted experiments, the results are emphatic, and show that, except in very sandy soil, the phosphoric acid does not reach, the roots of trees, hut is retained in the upper few inches, even in the presence of .a heavy rainfall. Using a high grade superphosphate carrying 17 per cent., of soluble phospheric acid, it was found that heavy cla> soils would retain 10001 b. an acre in the upper 3in., that loam soil would hold that amount in /6in., while a sandy soil would allow it to pass quite deep. He adds that he Was struck by this "locking-up" of phosphoric acid at the surface in the examination of the soil of an orange orchard where liberal applications of phosphates had been made for many years. The examination of th« soil (black clay) showed that the amount of phosphoric acid in the upper 6in. was .30 per cent., while in the next 6in., and still deeper, the percentage was only .05. Evidently the upper 6 in. had retained all the phosphate; that had been added .in many years.