Monitoring cobalt status - experiences in the central North Island

Abstract

The requirement for 'cobalt (Co) of ruminants grazing pastures on the pumice soils of the Central Plateau was established in the late 1930s and Co topdressing to increase the Co intake of animals became commonplace from the mid-1950s. An on-farm survey in 1978-79 indicated that Co inputs could be halved because of adequate reserves of soil Co accumulated since the 1950s. However, the economic downturn in agriculture of the 1980s led to marked reductions in Co use. Follow-up surveys between 1991-93 indicated a general decline in soil and pasture Co levels. This decline was much more pronounced in areas with a poor history of Co topdressing. The 1991-93 survey results indicated a relationship between soil Co and pasture Co, Using probability analysis it was possible to indicate the soil Co level required to maintain a particular pasture Co concentration. Keywords: EDTA soil cobalt, fertiliser practice, pasture cobalt, stock health