FOR A reliable indication of how efficiently a dairy herd is working, take a look at the slurry store – that was the view of visiting Kiwi farmer and consultant, David Law, at a recent series of meetings organised by Envirosystems.

"Contrary to popular opinion, a crust on slurry is not inevitable," he told farmers at the meetings. "But it does tell you there is something wrong and that money is there to be won by putting it right.

"Although straw bedding can make a contribution, this is small in comparison to undigested fibre that has passed through the cows and forms the crust."

An approach developed by Mr Law is to think of a dairy system as four interconnected parts – soil, grass, cows and slurry – which he calls a BioCircle. "Fundamentally, this begins and ends with the soil and the ways in which it affects grass quality," he explained.

"Whether grazed or conserved, this impacts the cows, then the slurry impacts soil biology – either for good or ill."

Starting with the soil, Mr Law advocated two main steps: "First, have you soil analysed, not just for pH, nitrogen, phosphate, potash and sulphur, but also 12 addition elements covered by a more thorough system.

"Based on this, with independent interpretation and advice, make a plan to correct soil pH to 6.4 in conjunction with correcting mineral imbalances, particularly calcium and magnesium.

"Next, consider the impact, not always for the better, of your slurry on soil and grassland," he said. "From a crusted store, even after breaking up with a stirrer, slurry is likely to be dominated by anaerobic bacteria that have proliferated during prolonged oxygen deprivation caused by the crust.

"Not only will the foul smell upset your neighbours, this septic, acidic and toxic soup will contaminate your topsoil and damage its delicate population of micro-organisms, which are critical for growing healthy, high nutrient and palatable grass.

"First, correct the slurry's pH to 7.4, otherwise it will continue to acidify (lower the pH) of your soil. Make sure you use the right sort of lime and correct quantity for this, consistent with the soil analysis and corrective action plan."

Instead of burning diesel to tackle problem crusts, David Law uses a bacteria and enzyme cocktail imported to New Zealand from the UK, where it was developed by Envirosystems.

"If you correct the slurry pH and follow the instructions exactly, you will see the crust gradually disappear," he pointed out. (Time-lapse photography of this taking place can be seen at https://youtu.be/GDCzic2KhXY).

"After a few weeks, you end up with 100% liquid that is easy to spread with little odour. When they first see this, farmers can't believe where the solids have gone.

"The answer is that they've been digested by the slurry bugs and converted into aerobic bacterial organic matter, suspended in the liquid. On the surface, it looks like pond water.

"That bacterial matter is nectar to soil organisms. It promotes oxygenation of the soil and, as it breaks down, releases a rich supply of nutrients that feed soil organisms and plants alike."

In the resulting pH-corrected, chemically balanced and biologically active soil, Mr Law's 'BioCircle' sees nutritionally optimal grass being produced. When fed fresh or conserved, this balanced forage is ideal for the cow's rumen, where most of the fibre content is broken down to release nutrients.

The resulting dung has a much lower fibre content than before. This creates a slurry that doesn't crust. Instead, it remains aerobic and, with stimulation from slurry bugs and enzymes, powers it around its next revolution.

On his own farm with this system, David Law witnessed a 33% increase in grassland productivity from 35 to 47 t/ha (14 to 19 t/ac), at the same time as reducing nitrogen fertiliser from 188 to 38 kg/ha (50 to 30 units/acre).

He said this transition saw a corresponding increase in clover content to about 35% of the sward, ideal for combining herbage yield and protein content.

In conjunction with Envirosystems, dairy herd manager, Dave Lievesley, is pioneering the BioCircle approach in the UK and added that dairy farmers who can match progressive arable farmers in improving soil health can expect markedly higher grassland and animal productivity.

"In arable farming, healthy soils are all the rage for very good reason," he said. "They produce more plant life and higher yields of saleable crop. The same applies not just to grassland reseeds, but permanent pastures too. It's just less obvious.

"Good soil health depends on a below-ground population of micro-organisms. In a typical soil, 1 ha contains about 50 tonnes, mainly worms, eelworms, bacteria and protozoa."

Above ground, Mr Lievesley points out that 1 ha will support about two dairy cows. Under their feet, the soil's micro-livestock are equivalent to about 67 cows.

Without these, he suggested, the two cows above ground would not get fed, explaining why soil health needs to become a hot topic in grassland farming too.