Grass is the cheapest source of nutrients for ruminants, with an average production cost of only 6c/kg DM. In comparison, bought-in concentrates cost 25-35c/kg DM. As cost pressures continue to rise for livestock farmers it is increasingly important that they get the maximum production from their pastures.
And yet, down on the farm.....
  • Milk from forage is in long term decline and dropped below 2000 litres/cow for the first time in 2013. Efficient grassland farmers are achieving 4000 litres/cow from grass.
  • Beef cattle average daily liveweight gain on grass is 0.80kg compared to the potential of 1.20-1.30kg.
  • General dissatisfaction with grass growth from reseeded pastures is widely reported.
  • Feeding value of grass silage has stalled over the past 10 years.
  • Mineral trends for grass silage over the past 20 years has shown an approximate 50% increase in Potassium, a doubling in Iron and a 33% increase in Molybdenum. All three elements are implicated in cattle nutritional disease as risk factors for hypocalcaemia, depressed immunity and infertility respectively (T&J Survey).
At a time when livestock production should be becoming more forage dependent, in reality the reverse is occurring. The answer to the decline in yield nutritive value and contribution of grass to milk and beef production lies in the soil.
Soil Compaction

"Soil compaction is the greatest threat to grassland production and can reduce yields by up to 40%" - Grassland & Muck, 2014. An established 70% of grassland soils in England and Wales exhibit severe or moderate soil compaction.
Soil compaction has many causes including:
  • Intense rainfall (1" of water per acre weight 101 tonnes).
  • Cows poaching.
  • Heavy machinery.
  • Excess slurry applications (Ammonia destroying soil structure).
  • Soil mineral imbalance (high Magnesium – low Calcium soils).
The consequences of compaction include:
  • Grass growth reduced by up to 40% - ADAS (2014).
  • Fertiliser requirement increased – Nitrogen by X 2.5 to achieve the same yield – Douglas, J.T. & Crawford, C.E. (1993), Grass Forage Science, 48, 91-100.
  • Root penetration reduced – Taylor, H.M. et al (1966), Soil Science 102, 18-22.
  • Earthworm counts reduced by 95%. Radford, B.J. et al (2001), Soil Biology & Biochemistry 33, 1869-1872.
  • Nutrient run-off increased. Environment Agency.
  • Soils take longer to warm up in spring. Personal experience.
  • Soils are biologically dead. T&J Soil Analysis data.
  • Anaerobic soils resulting in residues degrading more slowly and an increase in the solubility and uptake of Iron and Molybdenum by grass.
The bottom line is that compaction squeezes AIR out of soils, and AIR is just as essential for life below the ground as it is for life above. As soil life declines, so soil fertility, which is the ability of soils to supply nutrients to plants in a sustainable way, is reduced.

Soil Life
Soils comprise a myriad of dependent complex life forms from microscopic bacteria and fungi, through protozoa, nematodes and arthropods, to earthworms. But it is earthworms that are the most visual sign of soil life.

Healthy soil is reckoned to have over 3 tonnes of earthworms per hectare, which is considerably more than the weight of livestock grazing on the surface. They consume over 15 tonnes of soil during the course of a year which is essential for nutrient cycling, drainage and building a stable soil structure which is more resistent to soil compaction. Look for 15-20 worms in a typical spade-hole if the soil is in a healthy state. The other significant threat to soil life is excessive application of putrid, anaerobic, smelly slurry. Cattle and especially pig slurry contains a high level of Ammonia, which is highly toxic to worms. The sight of gulls following the slurry spreader and picking up dead earthworms used to be all too common, but on many farms now the birds stay away because the worms have long gone.
So, compaction reduces soil life, which is further compromised by slurry, resulting in up to 40% less grass yield. In addition, the mineral balance of grass changes with higher levels of Potassium, Iron and Molybdenum increasing the risk of hypocalcaemia, infertility and poor cow health.
Dig a Hole
To assess the extent of soil compaction, dig a hole. A spade's depth and width will provide a wealth of information not only on compaction but also soil health and fertility.

Look for the following criteria:
What to look for:  Soil Fertility
  Good Poor
Compaction Not apparent Surface compaction
Texture Uniform Horizontal compressed bands
Smell Earthy Stale
Colour Brown Grey and mottled
Rooting Depth Deep Shallow
Earthworms 15-20 <10
Drainage Effective Surface waterlogging
The photo above shows a typically surface compacted soil with a horizontal band of compressed soil at 10-15 cms deep, just below the grass line. Going below this compacted zone the soil is more crumbly and open. Rooting is shallow and no earthworms can be seen. Definitely a soil with poor fertility and not achieving its potential in growing grass.

At a time when livestock farmers are being encouraged to grow more grass and to produce more milk and meat from forage, soil compaction is the single biggest threat to achieving these aims.

The key actions required to improve soil fertility are to get AIR into the soil, keep it there and support soil life. In 2013, in conjunction with Devenish Nutrition, a Soil Improvement Plan was developed based on:

image21. Aeration – to disrupt surface compaction and get AIR into the soil. Most of the soil nutrients and biological activity is in the top 15-20 cms. The Cahill McKenna Aerator was selected because of its design and work load. It can operate up to 15km/hour and has the capability to cut through the surface compacted layer allowing air penetration and improving drainage.
2. Improving Soil Structure – to keep AIR in the soil and make it more resistant to compaction. It has been recognised for many years that high Magnesium soils are "sticky" and more liable to clump and compact. High Calcium soils are more "open", but again are potentially unstable leading to collapse and compaction. Getting the Calcium-Magnesium balance right for a stable soil structure involves a soil analysis. Corrective actions can include liming, or the application of Gypsum (Calcium Sulphate) or Kieserite (Magnesium Sulphate). Building a stable soil structure which has a higher resistance to compaction is crucial to ensuring air penetration in support of soil life.
3. Composting Slurry – converting slurry from a putrid, toxic waste into a valuable fertiliser nutrient source that supports soil life requires an aerobic digestion or composting process to occur. The benefits to soil life and fertility of applying well rotted farm manure are well known.
Translating this principle to slurry can have the same positive effects. BioAg's Digest-it liquid microbial composting culture has been proven to improve Nitrogen levels by 33% by converting Ammonia into the more stable Organic-N form. It also progressively composts slurry by moving the microbial balance from anaerobic (putrid) to aerobic (composted). Slurry solids are digested producing a more uniform slurry which requires less energy to stir, pump and spread. Surface crusting is reduced and odour gradually dissipates. A cost effective ratio of 3:1 in slurry fertiliser nutrient status has been shown from the composting action of Digest-it.

Building and maintaining soil life and fertility using the Soil Improvement Plan will have the following benefits:
  • Increased grassland production.
  • Higher feeding value of grass.
  • Improved mineral balance and reduction in risk factors to cow health.
  • Environmental benefits from reduction of potent anaerobic greenhouse gases such as Nitrous Oxide, Methane and Hydrogen Sulphide.
  • Increased livestock production from forage, which means more opportunities for mineral supplement sales.
Monitor Farms
Lakeland Dairies have agreed to establish monitor dairy farms to evaluate this Soil Improvement Plan over the next 3 years to measure its impact on both grassland productivity and cow health.

Soil compaction is the greatest threat to achieving the improvements required in grass utilisation by dairy and beef cattle to meet the farming industry's future expansion plans in an environmentally sustainable way.
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