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Management of the soil is the key to profitable livestock production, Welsh grassland consultant Charlie Morgan reminded farmers during the first of two online sheep events taking place this month.
Organised by various industry organisations including the UFU, CAFRE, AFBI and the National Sheep Association, Morgan told attendees that a failure to supply nutrients to soil means that low-quality grasses and weeds take over.
The resultant material is then unable to support even low level animal performance.
The starting point was a 25-year-old sward
To illustrate his point, Morgan outlined the results of a study he was involved in during the 1990s on an 18ac plot of land in Brecon Beacons national park, Wales, which investigated the implications of reducing fertiliser inputs on subsequent sward output.
The starting point was a 25-year-old sward, mainly dominated by perennial ryegrass and creeping bent.
Six treatments were used:
1 Soil pH, phosphorus (P) and potassium (K) were kept at optimum levels, with 150kg nitrogen (N)/ha applied each year.
2 As per treatment one, except the N was removed.
3 No N, P or K was applied. The only input was lime to maintain pH at optimum levels.
4 No inputs were applied.
5 No inputs were applied. Area was cut once per year.
6 The area was totally abandoned.
In treatments one to four, sheep maintained the sward height at 4cm (1,500kg DM/ha).
Numbers of ewes varied across treatments, and during the year, to keep the height consistent. No topping of swards was done until the end of the growing season, so weeds were left to flower.
Moving across the treatments, the proportion of perennial ryegrass in the sward was highest in treatment one, but was gradually replaced by unproductive grasses, falling to zero in treatment six.
Thistles were low in the first treatment, but started to increase in treatment two, peaking in the third, before falling back in treatment four.
“As you reduce the nutrients, the thistle ingress was increasing, but also when you take out the nutrients altogether, you start not even being able to grow weeds,” said Morgan.
Clover was highest in the second treatment, and also performed quite well when just lime was applied.
“But once you start taking the animal away, clover starts to disappear,” he added.
Stock carrying capacity
Unsurprisingly, the first treatment was able to carry the highest number of animals per ha.
The second treatment, which created ideal conditions for clover, saw stock carrying capacity at around 75% to 80% of treatment one. When P and K were removed (treatment three) this fell to 50%, and when neither fertiliser nor lime was used (treatment four), it reduced to 45%.
“If you have got a Scottish holding with 5,000ha and one ewe per ha, that is maybe OK [to apply no inputs]. But if you are on smaller farms, you have got to have a certain number to have a turnover to generate a profit,” said Morgan.
He also emphasised that there was a significant knock-on impact on animal health, welfare and, ultimately, performance when perennial ryegrass in swards was gradually replaced by unproductive grasses such as creeping bent.
The genetics were the same – the only change was nutrition
Despite lowering stocking rates down to one or two ewes per acre in the low-input treatments, Morgan said that ewes struggled, being 6kg lighter on average, with lambing percentages 10% lower, and replacement rates higher as teeth and udders didn’t last as long.
“The genetics were the same – the only change was nutrition. You can’t ignore feeding and managing your soil if you want to achieve good animal performance,” he said.
Lessons
The outcome of that 1990s study highlights the importance of having at least 50% ryegrass in swards.
Where old grasses are allowed to dominate, the field might still look green, but it is less responsive to fertiliser, and with significantly lower D-value and ME.
They won’t graze this old grass that deep, they would rather starve than eat some of this poorer-quality grass
“We talk about grazing pressure and grazing heights and getting sheep to graze down to 1,500kg DM/ha. They won’t graze this old grass that deep, they would rather starve than eat some of this poorer-quality grass,” said Morgan.
He also said he was “horrified” by how few farmers are able to identify a perennial ryegrass plant, and encouraged farmers to adopt rotational grazing systems, pointing out that it can deliver other benefits beyond just better utilisation of grass.
In particular, he maintained that in set-stocking, livestock tend to congregate in one part of the field, whereas in a paddock they are forced to graze and fertilise the whole area. That will encourage biological activity, leading to improved soil structure, negating the need for machines to alleviate compaction.
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