A dairy farmer recently asked, “as fertiliser this autumn will be paid for with borrowed money what is the least I can do without harming next season’s production?”
The short answer is, maintaining animal and soil health over winter and spring will ensure both grass and animal production are maximised, and this is usually easily achieved.
On magnesium deficient soils, dolomite applied at 200 –250kg/ha this autumn provides a range of benefits. For all intensive dairy properties with the exception of those on soils naturally high in magnesium, the same rate applies with the same benefits provided.
The first benefit is a general improvement in overall animal health, and in the short term that may simply be an improvement in animal demeanour. Animals receiving less than their required daily magnesium are likely to become irritable and easily disturbed.
Animals have relatively small magnesium reserves able to be readily mobilised so it is important that animals, particularly lactating animals, ingest their required magnesium intake daily. The most efficient and effective way of achieving this is ensuring there is sufficient magnesium in every mouthful of feed eaten.
A single dressing of dolomite applied annually nearly always achieves this provided potassium inputs are kept at rates necessary to maximise pasture growth. Providing excess in order to lift soil levels usually results in excess potassium in the leaf of plants at the expense of the other major cations, calcium, magnesium, and sodium.
When soils are moist, as they are throughout late autumn and winter, potassium deficiencies are unlikely. As soils start to dry out with the onset of summer potassium may limit growth so deferring potassium inputs until then is sensible. Herbage and soil tests provide useful information.
The second benefit is the reduction in calcium/magnesium related metabolic disorders in spring. Metabolic disorders at this time are seldom a single element deficiency. Where there is a deficiency of magnesium it is likely that calcium is also deficient.
Dolomite contains both calcium and magnesium in the ratio of 2:1, close to the ratio in grass throughout winter and early spring. This is one of the reasons for the exceptional effectiveness of dolomite in reducing the number,and severity, of metabolic disorders at that time.
Lack of energy increases the likelihood of animals requiring treatment. One of the important requirements for energy formation in grasses is calcium and dolomite helps ensure a plentiful supply.
Severe metabolic disorders in spring can also be caused by a lack of sodium. This is unlikely in close proximity to the coast however further inland sodium supplementation may be beneficial. Salt blocks are an easy and efficient way to ensure sufficient sodium is available.
The three steps to outstanding animal health this autumn, winter, and spring, are withhold fertiliser potassium, make salt available, and apply dolomite at 200–250kg/ha.