Scotland’s wet winter and late spring has put silage-making behind in some parts of the country, with difficult decisions now needed to ensure adequate forage quantity and quality for the coming winter.

Second cut silage is going to be more important than first for many Scottish livestock producers this year as grass in many parts of the country was exceptionally slow to get going following challenging conditions for growth in the spring, said independent grassland specialist Dr George Fisher.

With the start of the cutting season delayed due to months of wet weather, variable soil nutrient levels and a late spring, livestock producers were faced with waiting for growth to bulk up or take a cut as soon as possible, he pointed out.

“Grass was so slow to get going and then, for many, there was a huge surge, which was difficult to manage. Those that cut close to normal timings have poor first cut yields, but the regrowths are OK.

“Those that waited for bulk got lower quality and the regrowths will be slower. There’s a real risk that many producers could go into the winter critically short of forage quantity and quality, unless some difficult choices are faced up to now.

“Importantly, those farmers who have made the decision to delay taking the usual early cut need to think carefully about what this will do to grass growth for the rest of the season.”

Those leaving swards beyond the usual first cut window could be storing up major problems later, he warned. He said it was better to take cuts as close to normal as possible and then pay attention to the state of the soil and the nutrition needed to help second, and third cuts.

“Research from SRUC's Crichton Royal Farm shows that poaching from livestock can check grass growth sufficiently to reduce yields by 15%, whereas deeper compaction from machinery wheelings can reduce output by up to 25%,” he argued.

The only way you can tell if this is limiting growth is to dig and assess soil condition at various locations in the field, he said.

“Wheelings can cover up to 85% of a field used for silage production so the chances are compaction will exist. Use a spade to dig three sides of a square then lift the turf up and take a good look for obvious pans.

“Compaction created by sheep typically exists in the first 2-inches of the soil profile whilst that from cattle could be at 4-inches of depth. Damage from machinery wheelings, meanwhile, will usually be from 4-inches deep and beyond.”

It reduces soil microbe populations which, in turn, limits those making nutrients from soil organic matter, manures and purchased fertilisers.

“Sward lifting can be an effective way of addressing these problems, but it has been shown to reduce grass yields by up to 10% in the four weeks after it is carried out. That is not something you want to risk.

“If compaction is only in the top 5-6-inches then 'spiking' will get air into it and while this can improve soil microbes and structure, it is essential to get below the compaction to allow water to drain and get air.”

Another issue that impacts on yields is the use of urea as a fertiliser. Farmers need to be careful with this.

“Trials have consistently shown urea is a false economy for grassland, looking at the big picture. It is tempting to use because of its lower price, but it almost always limits production.

“Trials at Reaseheath College, in Cheshire, have shown savings of £1900 from using urea over Nitram ammonium nitrate on an 80ha system, but this also resulted in a 17% loss in grass yield, worth at least £8500.

“Even with inhibited urea, which is designed to make nitrogen loss to air less of a problem, a 15% reduction in grass yield compared to ammonium nitrate was seen,” he said.

The main problem is weather and its effect on urea stability and utilisation, he said. “With urea, you need significant rainfall within three days of application to wash it into the soil where the microbial urease can convert it into nitrate. Without that, losses to air through volatilisation make it wholly uneconomic.

“In most years, there’s generally only a 30% chance of getting an economic benefit from using urea over ammonium nitrate.”

CF Fertilisers’ regional manager for Scotland, Mark Garrett, says as well as applying nitrogen carefully, soil pH, P and K need to be taken into account.

“Soils with low pH are generally pretty inactive and unlikely to promote uptake of the key nutrients efficiently. Usually, grassland has adequate amounts of P and K because of slurry and FYM, but this may not be the case this year after high rainfall.

“Even if you put as much slurry and FYM on as possible earlier in the year, available nitrogen from this will largely have been used or lost.”

Sulphur behaves like N in the soil, so if N has been lost, you will have lost sulphur, too, he added. “Trials suggest a 20-40% increase in DM yield are possible from using sulphur and it has been shown to lift protein and soluble sugar levels and 2016 could prove to be the year sulphur comes into its own on grassland.

“Work from your soil analysis and take into account all the nutrients from manures. For second cut you need to be typically looking at 80-100kg of N/ha, 60-90kg of potash/ha and 25-40kg of sulphate/ha to meet requirements,” he said.