Healthy Soil is Key for Quality Forage Production

Maximising milk from forage is the key to improved margins.

Every 1,000 litres increase in milk from forage will be worth around £100 of gross margin per cow regardless of production system. Forage is the foundation.

Maximising yield per acre is key, but regardless of forage type, fertiliser regime, weather or harvesting method (grazing or mechanical) soil conditions will have the biggest impact on both quality and quantity.

Around 70% of soils examined will be compacted. Compaction can reduce grass yield by up to 40%; consequentially increasing productions costs per tonne of DM by 40%. Compacted soils will require 2.5 times more nitrogen inputs to achieve the desired yields.

Other negative implications of soil compaction include increased nutrient run off, increase solubility and uptake of Iron and Molybdenum and slower warming of soils in spring.

Tracking by heavy machinery, excessive slurry applications, poaching by cattle and sheep and soil mineral imbalances of Magnesium and Calcium will cause soil compaction. One must also not forget that natural phenomenon such as rainfall; one inch of rain is equivalent to 101 tonnes/acre, and of course gravity!

Compaction occurs when the soil structure is compromised as a consequence of the above.

Earth Worms are the soils living conditioners

There is more weight of living organisms in the soil than there are above it. This is why creating a well aerated soil is the key. In a healthy living soil earth worms account for 3 tonnes/ha of the total mass. Earth worms are responsible for recycling nutrients, especially organic matter from dead plant material and manures applied to the land.

In a year earth worms can consume up to 15t of soil improving drainage and stabilising the soils structure.

Ammonia in slurry however is toxic to earth worms which is why heavy slurry applications can reduce the earth worm population. Composting slurry prior to application is extremely beneficial to soil health and protecting the earthworm population. In addition it can improve the value of slurry as a fertiliser.

Composting or aerobic digestion increases the N content of slurry by up to 33% primarily by reducing gaseous ammonia losses and converting it into a stable organic form which is also less susceptible to leaching. The combined effect of safeguarding soils structure and increasing nutrient value is increased yields and quality.

Soil structure and health can easily be assessed by digging a hole and looking at texture, colour and the extent of root penetration. In addition the abundance of earth worms and the smell of the soil are also excellent indicators of soil health (Table 1).

Table Showing Soil Fertility
Table 1

Other indicators of poor soil structure include aerial tillering of grasses and an abundance of dead organic matter at the base of the sward. This dead material produces a stale smell which is off putting to grazing cattle.

The presence of seagulls following cultivation equipment or manure application is a good indicator of soil health and indicates the presence of a significant earth worm population.

Magnesium and Calcium balance in the soil has a profound effect on soil structure at the particulate level. High Magnesium soils tend to be sticky, whereas high Calcium soils tend to be more open but unstable. Getting the balance correct will make soils more resistant to compaction.

Soil health and mineral nutrition

There is a direct link between compaction and disease levels in dairy cattle. Compacted soils produce forage with high Iron, Molybdenum and Potassium content. This can increase the incidence of metabolic diseases such as milk fever, can effect fertility and impair the immune system.

Excess Iron content can reduce palatability but also increase oxidative stress. Reactive oxygen species can damage cell membranes and interrupt biochemical reactions in the body. More importantly there is a strong correlation between oxidative stress, mastitis incidence and retained foetal membranes.

Molybdenum is a copper antagonist, so high levels in forage will increase the dietary requirement for copper. The Molybdenum/Copper axis does have a role to play in the impairment of fertility but to date it is unclear whether Copper deficiency caused by excess Molybdenum or simply excess Molybdenum is the cause.

Three stages of soil improvement

In the first instance it is important to analyses soils for Calcium:Magnesium balance and correct as appropriate. This will include the application of Calcium and Magnesium sources such as Lime, Gypsum or Kieserite.

Mechanical aeration of compacted soils is essential. Compacted soil profiles generally occur between 4” to 6” below the soil surface, deeper compacted layers may be present at greater depths. The method used for improving soil aeration will be dependent on the location of the compacted layer which can be identified easily by digging a small hole to evaluate the soil profile.

Aerobic composting of soil is an important process for improving soil structure. Composting slurry can be achieved by the addition of slurry bugs to the store. Composted slurry will have an improved nutrient value and be less prone to crusting. This will reduce the power requirement for mixing and making the material easier to handle.

Well managed soils will produce grass with higher protein contents provided sufficient but not excessive quantities of sulphur are applied. The concentrations of Iron, Molybdenum and Potassium will be reduced promoting better animal health.

Improving soil health is a cost effective strategy to improve nutrient utilisation, forage quality and animal health. It is worth remembering that forage is the foundation of profitable milk production but this is underpinned by good soil health.

If you would find out more about agronomy and animal nutrition please contact us for advice and help on getting the most from every acre.

Written by Dr Huw McConochie  – Wynnstay’s Head of Dairy Technical Services
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