A dairy farmer entering his fourth season on a large dairy conversion phoned to ask whether an application of dolomite would help relieve the growing number of calcium/magnesium related problems on his property.
As that question could not be adequately answered without at least knowledge of current soil nutrient status and past fertiliser inputs the call took some time, with several pieces of extra information providing a clearer picture.
The entire farm had been cultivated in the autumn prior to dairy cows being introduced. At that stage there had been no known applications of fertiliser nitrogen. Initially pugging damage was minimal even in extended periods of wet weather, with excess moisture draining freely without ponding
Animal health during the first two springs had been largely trouble free. Calcium/magnesium related metabolic problems had been few, cows calved without difficulty, the occasional mastitis case easily and effectively treated, with somatic cell counts remaining low throughout both seasons.
The third spring had been more challenging with a range of issues requiring extra time and effort. The number of calcium/magnesium related problems had increased particularly amongst older higher producing animals. The incidence of mastitis also increased with somatic cell counts remaining stubbornly high at times.
Is it possible that all issues are related? The downward pressure exerted by the feet of heavy animals is significant, and as soils are ideally by volume 25% air, 25% moisture, and 50% solid, compaction particularly in periods of wet weather can readily occur.
Reduced air content reduces the activity of beneficial soil organisms as they rely on a steady interchange of air entering and gas being released. Under intensive dairying soils will often compact at 75 – 100ml, slowing the ability of excess water to drain freely, with the soil above the developing pan more easily scuffed and pugged.
With plant roots concentrated in the top 100cm, soil moisture content and chemistry rapidly change. The potassium content in the leaf of pasture often increases significantly during periods of wet weather at the expense of calcium and magnesium, which are more tightly held.
The question of whether compaction is inevitable is then open for discussion. Under treading pressure soil compresses, compaction occurs when it does not return to its ideal state. This is not inevitable and careful management is required.
When the ideal levels of calcium and magnesium are obtained soils are much less likely to compact. The ideal levels are best ascertained by soil testing. In all situations where magnesium is required Golden Bay dolomite is the most effective input.
For an intensive dairy operation a single application of dolomite at 220kg/ha provides 25kgMg/ha, sufficient for one season, and 53kgCa/ha, approximately one quarter of the required annual calcium input. Due to the fineness of grinding the release of nutrient can be rapid with a marked improvement in animal health achievable within three weeks of application.
Dolomite also has a strong conditioning effect on the soil, increasing the crumb content, reducing the likelihood of compaction occurring and as with all living systems when one aspect of health improves every aspect improves.