The cobalt status of Tasmanian soils. II The recovery of applied cobalt in pot experiments

Abstract

In glass-house experiments, cobalt was added at rates corresponding to 18, 32, or 36 oz CoSO₄.7H₂O per acre to 27 soils, mostly krasnozems. This treatment raised the cobalt content of subterranean clover tops significantly on only 13 soils, and on only five of the 13 by more than 0.05 p.p.m. Cobalt in control plants ranged from 0.05 to 0.32 p.p.m. The largest recovery of applied cobalt, by two successive crops of subterranean clover, was 4% of that applied. Mechanical contamination of plant material was avoided by adding the cobalt before sowing the first crop.

Perennial ryegrass and white clover gave similar results, over four or five harvests. The implications for the practice of top-dressing pastures with cobalt salts are discussed.

Cobalt application at the 36 oz rate increased cobalt in subterranean clover more than the 18 oz on three of the four soils tested at the two rates. There was some evidence for a greater recovery of applied cobalt from the more acid soils, over a pH range of 4.9 to 6.2.