The relationship between extractable soil cobalt and the cobalt content of ryegrass and red clover grown on 12 New Zealand soils : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science (Honours) in the University of Canterbury

Abstract

In New Zealand soil tests for macroelements such as phosphorus, sulphur, magnesium and potassium are satisfactory but there is a distinct lack of such tests for the micronutrients. New Zealand soils are not naturally fertile and often contain only small amounts of micronutrients. This is aggravated by the fact that these micronutrients have only limited availability in the soil and may be strongly retained by certain soil constituents. Cobalt: a micronutrient is essential for ruminant nutrition and for the growth and development of legume species. More precisely, cobalt is necessary for the symbiotic nitrogen-fixing bacteria associated with some legume species. As New Zealand pastoral agriculture is based on a low cost and low nitrogen input system, adequate supplies of cobalt are essential. Furthermore, the production of prime meat on these pastures, many of which occur on known cobalt deficient areas, benefits from good soil cobalt levels. With the movement towards more intensive agriculture and horticulture in New Zealand there is good economic reason for the development of a cobalt soil test to diagnose deficiencies and to provide both development and maintenance requirements. This project looked at total acetic acid-, EDTA- and calcium nitrate-extractable soil cobalt. Attempts were made to correlate these results with the cobalt content and uptake of perennial ryegrass and red clover grown on a wide range of New Zealand soils. Other soil constituents which affect the availability of cobalt were also considered. Species differences and the effect of the method of application on the cobalt content and uptake of the plant were studied.