How management can lessen the impact of dry weather

Soil matters
with Peter Burton
Functional Fertiliser Ltd

In our second season of sharemilking there was a major facial eczema outbreak in autumn. I remember the conditions well; it was hot and muggy with little wind and low cloud cover for what seemed like weeks on end.

Not having seen animals with facial eczema, and keen to be prepared, I asked farmer colleagues what to look out for and was told I would know when it happened and there was nothing that could be done in advance. At that stage Gladys Reid’s work with zinc had not been accepted.

In hindsight one of the things I found really interesting was that although the climatic conditions throughout the whole region varied little, not all farms were similarly affected.

Facial eczema

A large number of stock were affected on some properties, and others such as the one we were on had only one or two animals. The difference could not be attributed to irrigation, hedges, or trees, as there was no irrigation and all farms had hedges and a smattering of trees.

Daily management would seem to have played an important role in this situation. Pasture growth was slower than normal for late autumn and we decided to feed silage in order to lengthen the intervals between grazing, which was the only factor easily identified that may have lessened the impact.

Droughts would seem to fit a similar pattern. The word ‘drought’ evokes images of brown land devoid of all feed with skinny animals huddling together in an attempt to find shade, yet the photos of late from affected areas show animals grazing greenish pastures, a clear sign that there is still growth.

Why the difference?

Within the district there will be some farms drier than others and growing less feed, and the question is, why? Could the overuse of nitrogen fertiliser be a contributing factor?

Drought relates not just to the dryness of the soil, but also the ability of plants to grow, with different plants able to withstand drier conditions than others. Lucerne thrives in conditions where rye grass struggles to survive. Lucerne survives because its root system penetrates far further into the soil, allowing it to extract nutrient and moisture from further down.

Standard rye grass white clover pastures are reliant on moisture from closer to the surface, primarily the top 7.5cm, although plants in well-structured soils have roots to 30cm and below.

The key to retaining more moisture within the root zone of the plant is being able to increase carbon levels. Graham Shepherd states that “an increase of one per cent organic C in the top 300mm of soil can increase the soils capacity to hold water by 144,000 litres/ha”.

Soil carbon

Nitrogen fertiliser over time is known to deplete soil carbon, thereby reducing the amount of moisture available for plant uptake; the most likely reason for the rapid onset of slow growth when the intervals between rain goes beyond 10 days.

Less carbon also means less crumb, or aggregate, in the soil and the likelihood of a hard pan developing, often 7.5-10cm below the surface. Soils in this condition can easily be identified because grass plants will be growing on the surface, with their crowns proud, and easily removed during grazing.

The twin factors of less moisture retained and shallower rooting can have a marked effect on the length of a summer dry spell and when coupled with grazing intervals of less than a genuine 30 days, even a slightly drier than normal summer can become a genuine ordeal.

For more information call Peter on 0800 843 809.


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