Low soil fertility has paddocks under pressure

6 April 2011

Some of New Zealand’s farm paddocks are reaching a nutrient tipping point says Warwick Catto, Head of Research and Environment at Ballance Agri-Nutrients.

‘Many paddocks are now close to slipping below the levels required to sustain quality pasture and production, and if pasture composition deteriorates further the way back will likely be longer and more costly’

The need to keep farms solvent through tough times has seen farmers reduce or skip maintenance fertiliser applications and in some regions, no capital fertiliser has been spread for several years.

He says the dairy sector has generally been more careful about the continued use of fertiliser, but Olsen P levels in particular were now tracking down, with the average just above 40 on dairy farms.

The situation is worse on many sheep and beef farms, Mr Catto says, where farmers have struggled to accommodate the need to apply fertiliser due to the lower relative returns. As a result, productivity and pasture quality have been impacted directly.

‘We are seeing typical Olsen P levels on sheep and beef farms in the low 20s, with some dropping into the low teens.’

While some dairy farmers have been able to use the surplus nutrients in their soils, sheep and beef farmers typically had no comparable buffer. Dry stock farmers with declining soil fertility will already be seeing their ryegrass losing out to poor-fertility grass species, Mr Catto says.

‘Your soil fertility determines how long your winter will last It’s a double whammy: lower nitrogen fixation from the drop in clover content means less grass is grown, and the feed is of lower quality.

‘This creates a longer winter effect because you lose your cool season production. The poorer grass species that overtake the ryegrass and clover don’t grow at that time of year.’

Mr Catto says there are ways dry stock farmers can improve the situation, within the economic restraints.

‘The key is to protect your valuable production. Give fertiliser priority to new pasture, cropping land and your finishing areas. The fertiliser impact on poorer pastures will be less.

‘Talk to your spreader to exploit how nutrients move around the hillsides. Animals tend to gather at the tops so let them provide fertiliser for the tops, just put your fertiliser on the lower slopes and base of hills where nutrients are more likely to be of more benefit.’

For dairy, there’s an opportunity to manage the variability within each farm on a paddock-by-paddock basis, Mr Catto says. ‘We are seeing variable Olsen P levels across the farm in the range of 17-90. You can exploit that variability and realise production gains from the same quantity of fertiliser going on, by just varying where it is applied.

‘There is a lot to be addressed – soil pH is showing the same sort of paddock-to-paddock variability. Farmers might address their Olsen P one year, pH the next, then potassium. That will be a realistic, manageable strategy over time.’

Tests were also showing significantly lower soil sulphur (S) levels. ‘There is no reason why S – the cheapest nutrient – need be a limiting factor in pasture growth.

‘Doing nothing is only a short-term option. While prices are holding and returns are improving, now is the time to take some action.’

ENDS

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