Now that most farmers have started or are about to start the second round of grazing, it’s time to maximise grass growth to build up silage reserves. The rule of thumb for highly stocked farms is to have 100 units/acre of nitrogen spread by 1 May and another 50 units/acre spread in May.

Presuming the rotation length is 21 days, this means 32 units should be spread in each round. Lower stocked farms, farms with a lower silage requirement and farms with a lot of clover can and should spread less from now on. Sulphur should be spread on all soil types in April and May. About 16 units/acre of sulphur is required on grazing and 20 units/acre on silage ground.

For first-cut silage, 96 units/acre of nitrogen is required, 16 units/acre of phosphorus and 96 units/acre of potash is required, presuming soil samples are at index 3. Spreading slurry at a rate of 3,000 gallons/acre at closing will provide enough P and K. Extra P and K will be required at lower soil indexes.

Index 2 soils need 24 units of P and 120 units of K but no more than 96 units of K should be spread before closing to avoid milk fever and grass tetany, so spread the remainder after harvesting. Where land is now being closed for silage that got 70 units of nitrogen already and was grazed twice, only about 10 or 15 units of the 70 is still available for plant growth, so 70 to 80 units of nitrogen is required on these fields.

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