How to manage fertiliser effectively for first cut silage

High nitrogen prices make astute applications vital this spring

Rising input costs have seen fertiliser suppliers ramp up advice to help livestock producers get the most from first cut silage this spring.

Manufacturers say it is still possible to get a good return on investment – despite high fertiliser prices. Yara held a special webinar for farmers looking at ways farmers can get the most from nutrients.

Sulphur applications

Fields using a granular compound NPKS fertiliser can expect to see yields increase by up to 11%, according to Yara grassland agronomist Philip Cosgrave, who shared the findings from Yara/Farming Connect silage trials at three Welsh farms.

“With the typical cost of adding sulphur to each silage cut at around £7/ha, the extra grass grown in this trial – 300kg DM/ha – is worth nearly £50 in terms of energy and protein. That gives a healthy 7:1 return on investment.”

Many farmers believe a good response to sulphur is only possible on very light soils with low organic matter. But other trials have demonstrated a response between 10% and 37%, even on heavier type soils, says Mr Cosgrave.

These days, sulphur deposition in soils is at pre-industrial revolution levels, which affects yields and nutritional quality of grass. “We’re not getting the same amount of sulphur from the atmosphere, so we need to top up in some way.”

Organic manure is not enough, adds Mr Cosgrave, so using the right product with sulphur is important. That said, organic manure does have its place, especially when fertiliser costs are so high.

“Slurry is variable in nutrient content. It should be used primarily as a resource for phosphate and potash, rather than nitrogen, because 64% of the value in slurry comes from P & K.

“It’s worthwhile sending a sample to a lab for analysis or using a slurry hydrometer. For spring applications, we aim to optimise nitrogen content and use low emission spreading equipment.” 

Nitrogen rates

Reducing nitrogen rates by by 20kg/ha from the optimal rate of 120kg/ha will save input costs. But it will also reduce output. In Yara trials, applying only 100kg/ha of N with slurry making up 31kg/ha of N in both scenarios reduced grass yields by as much as 2t/ha.

“The cash cost of growing and harvesting the 120kg scenario works out at £20.07 per tonne, while the 100kg N rates comes to £20.08,” says Mr Cosgrave.

“Costs are lowered per hectare when applying less N, but the cost per tonne didn’t change, because most of the cash costs are charged on a per ha basis and not by yield.

“In this scenario, for grass produced, they’re no better off and have two tonnes of silage less, which is equivalent to 70kg of protein. It’s a balance and reducing N rates needs to be carefully considered.”

Another option for those considering lowering N rates is to delay harvest for a week or more, this will increase the rate of dry matter you produce. But this will also cause a decline in quality.

“In just one week, quality falls by 3.3%,” says Mr Cosgrave. “It’s not a straightforward decision. Consider all your options and whether allowing a longer period is right for you, as it obviously has an impact.”

Optimise nutrients

Yara offers a range of extra tips for getting the most from first cut silage this spring. Chief among these is focusing on establishing a strong nutrient management programme to ensure the best results possible.

“Creating a fertiliser plan is key,” says Mr Cosgrave.

“Calculate the NPKS requirement of the crop and determine how much you can provide with slurry and how much mineral fertiliser you need. Ensure sulphur is going in and don’t put apply any more than 90kg/ha of potash.”

“Optimising nutrient applications for your first cut is important. This is where we see the best nutrient response, and ultimately helps produce the best quality silage.”