Thursday, 24 February 2011

Hard to believe but Soil Liguefies in NZ Earthquake

I'm sure everyone (especially those who have visited NZ) feel for those people in Christchurch who suffered the devastating earthquake on the 22nd Feb 2011. We are all concerned for those people who lost family members & those who are injured & suffered massive damage to their houses & farms.

I've just returned from NZ & we (a Breton Discussion Group from France ) stayed in the centre of Christchurch for a week. To see the destruction in the CBD is frightening & very sad. Outsiders will be unaware that since the Sept earthquake there have been more than 4000 after shocks. Nerves are strained as everyone is not sure whats happening next. Very scarey!
Our group was hosted by staff of Ravensdown, Cropmark, Lincoln University, Farmwise, Consulting Officers & numerous very generous dairy farmers.....we sincerely hope that you & your families & friends are all safe.
The damage to city buildings is obvious in most TV & YouTube clips.

What is not so obvious is whats happening to the soil. This is of huge importance to farmers & to every householder.
While visiting Darfield we were shown the extensive damage caused by the Sept 4th earthquake where there was sideway movement of soil by up to 4metres & upward lift of 1.5metres in places.....earthquakes are violent & have massive forces. See the photos at the top of the blog showing the massive sideway movement of soil/road & irrigation channels.
What is very scarey in big earthquakes is that the soil turns to liquid. The forces are so great that ground water & soil are mixed & pushed to the surface often causing flooding. The concept that soil could be liquefied will sound almost unbelievable to most farmers. Christchurch is built on an alluvial plain over a soft sedimentary bed so it is prone to liquefaction. It is liquefaction that probably explains why so many buildings have been destroyed despite the very tough building code aimed at earthquake protection. After the water drains away there are tonnes of structureless sand or silt left on the surface. These videos show the liquefaction of soil in Christchurch within minutes or hours of the earthquake.

Here is a technical explanation of soil liquefaction

Richard Christie from Ravensdown has sent me two photos of soil liquefaction that occured in central Christchurch within 2 hours of the big shake this week.The first shows the Avon River (normally only say 30cm deep with clear water) now in flood with liquified soil. The second is of the liquified soil being forced up thru new cracks in Tuam street outside the Ravensdown building in central Christchurch.

A number of Youtube video clips visually show how horrific it has been in Christchurch this week.
Everyone expects many aftershocks.....we sincerely hope this is the last big earthquake Christchurch & Canterbury suffers. To our Canterbury friends, fellow dairyfarmers & Agricultural support industry we are thinking of you!

Tuesday, 8 February 2011

"I Dream of Mountains..." & Amazing Pastures

Meet Charles & Jan Whitehead who farm below Mt Hutt, Methven in Canterbury NZ. They milk over 800 NZ XBred cows in two herds on a beautiful farm with stunning views of the Southern Alps & the ski field at Mt Hutt.The Whiteheads & some local Discussion Group members hosted the French Group from Brittany.
"I Dream of Mountains...." was part of Andre's thank you speech after we had completed our farm visit. In part it referred to the beautiful mountain background at Mt Hutt but it was also a "Martin Luther King" like speech that referred to the pinnacle of pasture management we had just seen on a very simple but effective grass based system. Our group was very impressed with Charles & Jan's farm & the simple grass based system that created the best pastures we saw thru out NZ. In NZ the nitrogen use has increased with milk price & one of the consequences is less visable clover on most pastures grazed by dairy cows. Its not the only reason for clovers demise as clover weevil has had a major impact in the North Island. At lincoln University dairy farm the clover has disappeared almost completely.

Charles is renovating pastures on a 10 yr cycle partly because of grass grub damage. He has used both a ryegrass/clover mix and a fescue/clover mix. Both looked to be very good with a strong presence of clover (Charles uses 200kg N/ha per year. Excellent quality pasture grazed hard with a relatively high stocking rate resulting in a very good pasture on the next round. A simple but effective use of the pasture wedge graph. The fescue was planted at 25kg/ha plus 6kgs clovers (both small leaf & medium leaf). He explained to the group that the fescue needed to be on a quicker rotation to maintain quality.
The photo below is of the Fescue/clover pasture.
His usual pre grazing target was 3100kg DM/ha with a target residual of 1500..
The pre grazing pasture quality was exceptional & Odille those boots are "Sweet as".