Hundreds of tonnes of compost were trucked onto Miah and Jenny Smith’s property after they bought it with Jenny’s parents and uncle in 2011.
They were trying to build up the precarious topsoil layer typical on light pumice country recently out of pine trees.
Coming from the rich farming country of Taranaki but prompted by the desire to own their own farm after years of waged and sharemilking positions, they knew their 250ha property was going to be tough going.
“We had driven past it before we bought it and said to ourselves ‘no, wouldn’t want to farm on that place’ but here we are,” Jenny said.
Like many south Waikato conversions the place was full of grass grub, insidiously gnawing away at new pastures and confounding efforts to build up a valuable level of organic matter in the topsoil.
An up-and-down contour makes pasture and stock management tricky while the soil is low in most key minerals including nitrogen, calcium and boron and pasture root depth is shallow at best.
Early on in a bid to build up organic matter Miah trucked in more than 3000 tonnes of compost over three years, which had some but not a great deal of impact on the organic content.
Then he was convinced by a friend to attend a seminar run by Paeroa seaweed fertiliser company AgriSea.
“I have to admit I was pretty sceptical and kind of thinking this could be a snake oil that we did not need but I went along anyway.”
The company has been operating for over 10 years processing a New Zealand native seaweed species, Ecklonia radiata, into a foliar spray for horticultural crops and pasture.
The unconventional product has not been without controversy. In 2009 soil scientist Dr Doug Edmeades described the product as “snake oil” when it won a Waikato sustainable business award.
Miah opted to put aside 40ha for a cold-turkey trial of the product, keen to see if it would at least help build some much needed soil depth by encouraging greater bacterial breakdown and organic matter accumulation.
Cold turkey meant stepping right away from conventional fertiliser application on that area, including dropping nitrogen.
Typically, farms converting to such an approach step down their nitrogen levels over about four years.
“Six months into it and the grass had gone yellow but I realised it was too late now, we were committed so may as well continue with the trial anyway.”
Now, in the third year of the trial, Smith says he would not recommend a cold-turkey approach to dropping conventional fertiliser but is happy with what his onfarm trial is starting to reveal.
“The most interesting aspect is what is happening underneath in the soil. The pH level has lifted by 0.5 from 5 to 5.5 on one site and the phosphate levels have not been mined out and dropped as I would have thought they would. Instead, they have stayed almost the same as before we started.”
Potash levels also remain healthy despite the tendency to leach on the light pumice soil.
Grass grub numbers have declined to almost zero on treated sites and, partly as a result of that, grass root depths are on average double those on conventionally treated pastures.
Smith says he has noticed the impact not using conventional nitrogen has had on the grass in spring with the rate of growth slower coming out of the cold winters than on nitrogen applied pasture.
“But overall we have still managed to graze those areas eight times in the year, the same as conventionally treated paddocks.”
The couple are now watching how the system responds to a “salad” approach to pasture sowing, where more than a dozen species are sown rather than a conventional clover-rye mix.
Costing about $150 a hectare more than conventional mixes, Smith said he was encouraged by the experiences of Dr Christine Jones from Australia, a proponent of mixed pasture swards for boosting a soil’s carbon-capturing capacity through better topsoil development.
The Smiths are optimistic they will share the experiences of the German Jena experiment where a highly mixed pasture was shown to consistently outproduce a conventional pasture treated with nitrogen.
The Smiths are conscious three years is a short time when it comes to long-term activity like topsoil creation.
However, they also recognise they need to be looking ahead to futureproof their business as the national spotlight on stock numbers and nutrient losses grows more intense.
