The importance of good soil health as the foundation of productive grassland, was the main topic at the recent Isle of Mull monitor farm meeting.
The 7600 acre (3075ha) Torloisk, one of the network of Quality Meat Scotland (QMS) monitor farms throughout Scotland, is rented by Iain MacKay on a five year Short Limited Duration Tenancy. He runs a pedigree Highland fold of 55 breeding females and approximately 850 ewes.
The current Torloisk stocking rate is 0.07 Livestock Units per hectare. At a previous meeting, Mr MacKay had told the community group he was trying to increase the farm’s stock carrying capacity.
To do this he aims to improve the grassland on some of the better, ploughable land, with the target of eventually achieving a stocking rate of 0.09 Livestock Units per hectare, which numbers-wise would mean an additional 350 ewes.
Dr Bill Crooks, a Senior Consultant and Soil Specialist with SRUC, Scotland’s Rural College, explained basic soil health principles to the community group, adding that soil improvement ventures demand a time investment of a minimum of several years.
“To maximise grass growth, four key aspects need to be correct and in balance: soil structure; pH; phosphate; and potash.
“To assess soil structure, dig a hole in the fields selected for improvement. This will show you the existing root development, and establish whether or not root growth is being restricted by compaction,” said Dr Crooks.
“Compaction limits the ability of plants to glean nutrients from the soil, so you need a soil which is free draining, with plenty of air spaces to allow good root penetration. Compaction also leads to drainage issues, with water logged soils being colder, resulting in slower spring grass growth, than in soils which are free draining.”
Dr Crooks explained that surface compaction is generally caused by livestock and/or rain. Deeper compaction is often the result of machinery, with ploughing sometimes creating a pan several inches below the surface.
“Once the problem is identified, select the correct solution from the available options of techniques and equipment. Whatever action is decided upon, it’s important to work just below the compacted layer, to ensure the entire layer is broken up,” advised Dr Crooks.
He also emphasised the importance of establishing correct pH levels in soil. “The optimum availability of plant nutrients in soils occur only within a small pH range. A pH of 6 should be targeted for mineral soil, and between 5.3 and 5.5 on peaty soil.”
Dr Crooks recommended soil sampling every three to four years, to assess pH levels, and to apply lime at between one and three tons per acre to lift levels, depending on soil analysis.
Any lime spread on Mull has to be shipped from the mainland, a prohibitively expensive venture for farmers working individually. In 2010, 16 Mull farmers, including monitor farmer Iain MacKay, combined to purchase and ship 900 tonnes of lime from Torlundy quarry, near Fort William. If there is sufficient farmer interest this year, a similar team effort will be organised by the Highland Machinery Ring.
Dr Crooks told the group that the target minimum phosphate level in a soil analysis is “Moderate”. Phosphate is important for root development and early season growth, especially in re-seeds, with clover being particularly susceptible to Phosphate deficiency.
To boost phosphate levels, the application of Triple Super Phosphate, if available, (it is currently in short supply), was recommended as the most cost effective, if your soils are on target for pH.
The third vital soil nutrient listed by Dr Crooks - potash - helps grassland plants maximise the benefits of available nitrogen, either bagged or natural, while also boosting disease resistance.
“Be aware that by cutting silage, you are removing large amounts of potash from the area of grassland,” cautioned Dr Crooks. “So it is important to carry out soil analysis to ensure you have accurate, up to date information on potash levels.”
The target figure, as with phosphate, is “moderate”. Dr Crook recommended countering deficiencies by applying Muriate of Potash.
He warned: “If planning to apply high rates of potash to grazing land, delay until after July. Application in the spring can cause grass staggers (hypomagnesaemia) in livestock.”
Dr Crooks also flagged up a Government-funded Grassland Technical Note on Fertiliser Recommendations, which is at http://www.sruc.ac.uk/tn652
The next Mull monitor farm meeting will be on 6th June.
For general information on monitor farms, plus detailed reports of meetings visit www.qmscotland.co.uk/monitorfarms