I put out 100grams per ha of cobalt fermented in 10litres per ha of lactic acid as a foliar last season. I was pretty impressed with the results on the sap test keen to play with it more next season and I’d probably start with halving the rate going little and often. I came about it because I had molybdenum in excess whenever I had clover in a sample. The theory was clover was accumulating molybdenum because it didn’t have enough cobalt to use it for nitrification. Also required for production of B group vitamins. Farmers used to mist cobalt on pastures here until Vitamin B12 injections became available then they stopped because they could just put it into the stock.