Improving Sherry River pastures

This story is one for the farmers.

In 1941, cobalt experiments concerning sheep were undertaken by the Cawthron Institute under the control of Theodore Rigg who became a leading figure in all aspects of agricultural research.  

Experiments on the importance of cobalt in overcoming stock ailments on the granite soils of Glenhope and the Sherry Valley had already been validated.

The next round of tests was to confirm the value of cobaltised superphosphate for topdressing pastures in the upper Sherry Valley. The experiments were to prove to farmers in the Sherry Valley that the use of cobalt in topdressing would enable them to produce fat lambs and sheep equal in quality with those produced elsewhere.  

Cobaltised superphosphate was compared with heavy applications of Southland and Kaka limestones as suppliers of cobalt.  A line of wether hoggets was drafted on 11 September 1940 into four even groups.

Each group was placed on a two-acre field which had been topdressed a week or two previous with the appropriate fertiliser.  

These fertilisers were (a) Superphosphate 2 cwt per acre (control),  (b) Cobaltised superphosphate 2 cwt per acre, (c) Kaka limestone—2 tons per acre with 2 cwt superphosphate per acre and (d) Southland limestone 2 tons per acre with 2 cwt superphosphate per acre.

The sheep were weighed regularly to watch their progress under the various treatments. By 27 October, the sheep had increased in weight by an average of 20 to 24 pounds per head, the greater increase being with the sheep on the cobaltised superphosphate and Southland limestone areas.

A month later, on 24 November, all the groups, except the cobaltised superphosphate one, were nearly the same average weight, having advanced 30lb since the beginning of the experiment.

The cobaltised superphosphate group had however, advanced 42lbs. From then onwards, all groups except the cobaltised super- phosphate group went backwards in condition, especially the control and Kaka limestone groups. In the control group only one of the original animals survived, while most of the animals in the Kaka limestone group became sick.

The Southland limestone kept the sheep in somewhat better health, but these late also went downhill.On the other hand, the sheep on the area treated with cobaltised superphosphate continued to increase in weight and at the end of April 1941 averaged 122 lb.

The results of the trial indicated therefore that the cobalt in the Southland limestone, corresponding to an application of about 2ozs of cobalt sulphate per acre, could provide a supplement of cobalt which would benefit animals over a short grazing period.

The current season’s results in Nelson showed, however, that the beneficial effect was short-lived and did not last sufficiently long to allow sheep to be held for a full season on deficient country.

Slightly beneficial results occurred on the area treated with Kaka limestone, but only to the extent that no deaths had occurred.

The use of cobaltised superphosphate at the rate employed in the trial was reported as having given spectacular results, which indicated that, for completely satisfactory stock health, cobalt supplements must be supplied for Sherry River animals.