Thursday 20 September 2012

Intensive sustainable crofting - lime

All other things being equal the most profitable farms are on the best soils; soils that are neither acid or alkaline but neutral, soils that are well drained but not drought prone and soils that are deep and well structured. Here on the West coast of Scotland, with few exceptions, we have thin, stony, acid soils in the lowest land classification category. In other words they are not inherently fertile. High rainfall, high wind speed and the short growing season compound the difficulty of growing anything.

Sanna Bay in 1968 shell sand and lime rich machair grassland above the beach
So where do we start if we want to increase production per hectare of grassland or arable?  Soil acidity has to be the first limiting factor. The soil analysis for my hay park shows it to be strongly acid, around pH 5.3  to neutralise it will require 2.5 tonnes of ground limestone per acre. I know, I'm  mixing metric with imperial measures, its my age.

Ground limestone is bulky, heavy stuff and it comes in 20 tonne loads, four times as much as I need. My neighbours need it too so we have ordered a load between us at £42/tonne. Its the distance, 50 miles from the quarry at Ft. William and the narrow roads that push the price up. Historically shell sand was carted up from the beaches but they are protected areas now. The ground limestone will be delivered in 1 tonne bags in the next week or two and applied with a borrowed lime spreader.

We should see an immediate return on the investment with more grazing and higher yield of haylage / silage next year and for several years to come. It doesn't end here. Next the soil needs phosphorous and potassium so that clovers will grow, fix atmospheric nitrogen and make our crofts more productive and sustainable.


Michael said...

The photo's interesting. Is the machair the flat green grass behind the dunes at the bottom left? I'm never sure if the dunes and machair are the same thing or different. I suspect the latter because I'm sure Alasdair Maclean says in his book that the machair was disappearing at Sanna.

Tom Bryson said...

Yes the machair is the relatively flat lime rich and species rich grassland behind the dunes. The lime, in the form of fragments of shells, is carried inland by the wind. The grazing and the infertility lead to high plant diversity.

Michael said...

I did find some old maps of Sanna which are fascinating. Hard to tell how much smaller the machair now is compared to before. I once tried to work out where the small lochan in this map used to be - you walk to the beach through a flat area that looks like it could have been filled with water once.

Tom Bryson said...

Dune systems are continually shifting and this would affect the extent of machair. You might get an idea of the change by comparing old aerial reconnaissance photos with Google earth images.