In last November’s edition of Agriculture Today, NSW Department of Primary Industries special projects agronomist Mike Keys analysed the value of sowing new pastures in light of the high cost involved.

Recent price hikes in the cost of fertiliser prompted a similar analysis of whether supering existing perennial pastures (including natives with subterranean clover) will pay.

"The story is remarkably similar," said Mr Keys.

"Only fertilise where necessary, fertilise pastures and landscapes that have productive potential and make sure you can utilise the extra feed produced."

Mr Keys said guiding principles to assess whether returns will come from fertiliser input costs on existing introduced or modified native pastures were the same, provided the pastures were productive with good potential.

"The enterprise must be matched to the pasture and land class, with potential to generate a good income," he said.

"Stocking rates must be sufficiently high to capitalise on the extra pasture grown in response to the fertiliser, while ensuring the pasture is not over-grazed.

"Soil fertility levels must be known, any deficiency addressed and rates of fertiliser matched to the stocking rate and export of nutrients.

"Remember it is more cost effective to maintain soil phosphorus levels near the critical levels, rather than let them fall and have to build them up again later," Mr Keys said.

Newbridge long-term trial looks at best super returns

In 1995 soil phosphate levels averaged 11 milligrams per kilogram compared to a critical level (for 90 per cent sub clover production) of approximately 30mg/kg.

The district practice paddock received 125kg per hectare single super one year in three and ran five ewes per hectare.

Two other paddocks received 140kg/ha annually and stocking rates were slowly raised after a couple of years to peak at 7.5 ewes after six years.

The high super paddocks received nearly one tonne per hectare of super in the first three years, then a maintenance rate of approximately 160kg/ha annually.

Stocking rate was raised 20pc from day one and eventually peaked at eight ewes/ha.

In addition to recording livestock data, detailed measurements were taken of species composition, perennial grass persistence and soil fertility in each paddock.

Increased fertiliser did not destabilise native pastures or reduce the number of species present, provided annual species were grazed and not allowed to smother the wallaby grass in spring.

By November 2005, soil phosphate level in the district practice paddock remained the same as in 1995, in the annually supered paddocks it was 32mg/kg and in the high super paddocks it had been raised too high (for maximum cost-benefit) to 37mg/kg. 

Annual inputs win profit race

The table summarises financial data over 12 years, using actual stocking rates, lamb numbers, weights and sale prices but applying a 2008 superphosphate price of $465 per tonne for the entire period.

While the highest returns are generated by the high super regime, the best return on dollars invested was from the annual super paddocks, where stocking rates were slowly increased as the paddock grew more pasture.

It is unlikely a high input approach will achieve the best return on dollars spent, especially in the first two to three years, with current fertiliser prices.

It should be noted that simply reducing costs (inputs) did not increase profits, particularly as the cost being reduced was the one addressing the most limiting factor - in this case phosphorus, sulphur and molybdenum.

Once these deficiencies were addressed, legumes thrived, feed quantity and quality began to rise and more stock could be run.

Despite the higher stocking rates, all annually fertilised paddocks had significant numbers of lambs reaching the target weight of 38 kilograms at weaning.

Only one lamb ever reached the target weight (and thus higher dollar per kilogram value) from the district practice paddock.

"This work has clearly shown that modified native pastures can be productive and are not adversely affected by fertiliser application, especially if fertility is the most limiting factor to production as it was here," said trial organiser, Mike Keys.

"It is vital, however, to know what native grass species are in the paddock so that appropriate management can be employed to ensure their long-term persistence.

"As a general rule, more harm is done to native pastures by lax grazing or inadequate matching of pasture growth to stocking rate and stock requirements, than by hard grazing."

Also in this edition:

Bookham says value, despite a hike