7 February 2008 Lincoln University research reveals some answers for forest to pasture conversion

 

Land use conversions are today transforming the agricultural landscape. Fonner sheep farms now bustle with the daily routines of dairying; other land has been regimented into the parade-like orderliness of vineyards; urban fringe farmland is being parcelled up for housing development; and elsewhere, harvested pinus radiata forests are being converted to pasture.

Lincoln University's Associate Professor of Pasture Management Grant Edwards says that while there are a number of constraints to converting radiata pine forest to pasture, science has been able to help by clarifying the nature of many of the problems and offering research-based recommendations to deal with them.

At Darfield, 45 kilometres west of Christchurch, Lincoln University researchers have been working on a 30-hectare Selwyn Plantation Board forestry site logged in 2004 after a century of growing radiata pine. The project has been funded by Selwyn Plantation Board Limited.

Soils on the research site are Lismore stony silt loams, and rainfall on the block is a low, 750mm/year. Initial pastures were planted in autumn 2005 and lime was added to increase pH to 6.1, as well as 350kg/ha of superphosphate.

"Our research has been all about converting forest land to pasture in a sustainable way that will lead to productive and persistent pastures into the long term. The aim has been to investigate pathways and practices for achieving sustainable levels of productivity and minimal weeds," says Associate Professor Edwards.

Constraints identified in converting radiata pine forest to pasture included -
• Low soil ph of 4.6 to 4.9, which can promote relatively toxic levels of aluminium.
• A relatively high carbon to nitrogen ratio of more than 20 in the soil due to woody
debris, which is double the optimum for pasture on these soils.
• Large seed banks of woody weed species such as gorse and broom.
• Lack of structure in the soils following cultivation mulching after clearing of the pines, which makes the soils prone to erosion.

Trial plots included Italian ryegrasses, permanent perennial ryegrass pastures with white, sub and balansa clover, a triticale crop followed by permanent pasture, and then a sequence of triticale to rape, undersown with clover and followed by permanent pasture.

And the findings?

"Crops undersown with legumes appear to counter many pasture establishment problems when forest is converted to pasture," says Associate Professor Edwards.

"Overall the experiment on the site showed that annual forage crops like rape and triticale are much better to use before sowing permanent pasture on the Canterbury Plains.

"Pastures which had been cropped first with rape or triticale and undersown with legumes ended up with a very high abundance of legumes, and this was achieved at very little cost to drymatter production.

''The legumes provided not only high quality feed but high nitrogen inputs into nitrogen deficient soils. High legume pastures and luceme crops were also nearly free of gorse and broom.

"All the pastures produced about the same amount of drymatter, around 6t DM/ha, which showed it didn't matter if they had been undersown or sown conventionally."

For further information on this research contact Associate Professor Grant Edwards, Agriculture and Life Sciences Division, Lincoln University, email: edwardsg@lincoln.ac.nz.