Written by Victoria Rutherford

North Canterbury dairy farmers Kevin and Sara O’Neill have improved pasture quality by extending round lengths and applying different fertiliser mixes in a little-and-often approach.

Underpinning all their fertiliser decisions are Whole Farm Soil Tests (WFST) and the assistance of their Agri Manager, Eilish Burrows. If testing shows any paddocks are below optimum range for phosphate (P) and pH, they receive a capital application of superphosphate and lime to rectify them.

“WFST is a big driver for us when we catch up in the spring. Levels in some areas of the farm may have dropped or be trending down, so they might get a capital dressing. We are starting to build up a bank of trends now which is the key to making these decisions,” Kevin says.

“It’s a good way to give you a bigger picture and monitor what’s going on,” says Eilish.

The couple own two dairy farms at Culverden with contract milkers on both. Red Hills is 312ha, milking 920 cows at peak, and Pahau Reserve is 158ha with 510 cows at peak.

At Red Hills, 75% of the herd is wintered on (all mixed-age cows) while at Pahau Reserve 25% are wintered on and the remainder grazed out. Both farms are irrigated, currently with pivots and lateral shift gear, but they are moving to fixed-grid irrigators next spring.

The O’Neills operate with a stocking rate of 3.2 cows/ha on the pasture platform of both farms, excluding the wintering area. The pasture sward is a mix of ryegrass, clover and plantain.

They have five years of WFST data and have built a detailed view of each farm’s nutrient status and trends. Eilish also carries out herbage testing to monitor micro-nutrient levels, particularly molybdenum.

They had previously focussed on short round lengths to help maintain pasture quality, but have since increased from 18 days to 24 days after struggling to maintain sufficient clover population in the sward and ensure its establishment at higher rates of N.

“Six days in a cycle is quite a long time, a quarter of the growing length,” says Kevin. “We have found the grass is yielding better too.”

Targeting clover persistence in their pastures led the couple to investigate the use and timing of other nutrients, particularly sulphur (S).

When Kevin was sharemilking, he found that single annual applications of fertiliser were okay, but often created a feed pinch later in the season.

S also had the potential to leach out of the soil, especially in a wet winter. So he worked with Eilish to come up with a cost-effective mix that would ensure pasture growth and quality was maintained alongside the increased round lengths.

Single round applications range between 40–70kg/ha of urea, trending towards the lower end of input last season. “We have always been reasonably low, so the N-cap didn’t mean drastic changes,” Kevin says. After the first round in spring, both farms typically receive Ammo 36 (a blend of ammonium sulphate and urea at a ratio of 40:60). For subsequent rounds, a blend dubbed ‘Red Hill’ mix is spread to meet N, P, K and S requirements and keep pastures humming. “We apply the Red Hill mix to both farms, and review again in the autumn,” says Eilish.

“Sometimes it’s been a DAP mix with potassium chloride and a bit of granular ammonium sulphate (GAS). But this year with prices rising, we changed it to Sulphur Super 15 and Flexi-N with potassium chloride.

“So it’s a little and often approach – the pastures are getting N, P, K, and S every round,” Eilish says.

Kevin O'Neill with Ravensdown Agri Manager Eilish Burrows

More S was applied in their Red Hill blend last season because it was wetter than normal. Testing showed soil S was lower, so sulphur super was added to the Ammo 36 to ensure elemental S (which is not water soluble and therefore not subject to a winter drainage effect) would be there in the spring before soil microbial mineralisation converts it to plant available sulphate S.

“We went with more S than N because there’d been a lot of rain, and that definitely boosted things along,” Kevin says.

He is aware the science suggests that as long as applications of each nutrient are adequate, there is little difference in total pasture growth between his preferred little-and-often approach versus spring/autumn applications, except under very high rainfall.

However, he feels this approach better suits them.

“One of the big drivers for me was the comfort of having S going on right through the season to try to help that clover. We were concerned that when you’re putting P and S on at more leachable times of the year like the end of April, then you still have that whole winter to lose it.”

While the soil tests and the trends dictate the capital application, the maintenance applications following the cows are standard. When following the cows, it’s a set rate in the plan, allowing the contract milkers to adjust it to suit requirements.

“Anything that’s little and often has to be good in my mind, rather than having infrequent larger applications of P. It’s just about being more consistent,” Kevin says.

Eilish says looking at things from a different perspective, such as round length rather than focussing on the nutrient application rates, can be beneficial.

“With nutrients being expensive, it’s good to think outside the square about how things can be changed to achieve outcomes,” she says.

Kevin agrees. “Just because it was appropriate once, doesn’t mean it’s necessarily appropriate now. We like to fine tune. We are very cost-focused on both farms so any way we can find the savings is enough of a reason to investigate further and look at how we do things.”