Compost builds yield but what cost?
by Andrew Swallow
16/3/2010
Compost’s interaction with conventional fertiliser is being investigated as part of the Lincoln trial, explains Plant and Food’s Craig Tregurtha.Crop yields can be substantially improved by hefty applications of compost, a FAR organised field day near Lincoln was told recently.
However, limited supply, variable response and substantial delivery and application costs means it will need to be carefully targeted to be economic.
Trials in South Canterbury have already shown the yield enhancing potential of the product, 50t/ha applied prior to sowing boosting kale drymatter yield 50%, from 8t/ha to nearly 12t/ha, with a 25% benefit to the following year’s kale, though barley this summer, the third since application, didn’t respond.
“It looks like there’s very little in it in terms of grain yield though we did see height differences in the barley,” says Plant and Food Research’s Craig Tregurtha.
That South Canterbury work is ongoing with oats/moata already sown for winter grazing, to be followed by kale and possibly barley again after that, but a new, more in-depth trial with a more typical cropping soil and rotation has been established at Lincoln.
Following 0, 25t and 50t/ha applications of compost to deep, paparua silt loam on Plant and Food’s farm, forage maize was sown, to be followed by wheat this autumn, oats/moata for winter 2011 and a crop of peas or barley in 2011-12.
Compost has either been applied in one hit, incorporated into the Lincoln soil (it was broadcast pre direct drilling in South Canterbury) or will be split applied across the three phases of the rotation. Overlaying those plots are four nitrogen rates.
“We’ve tried to make it a fairly typical arable rotation but also to make best use of the trial opportunity,” says Tregurtha.
A recent history of intensive cropping and cultivation means the Lincoln soil is low fertility and structure is “shot”, notes Tregurtha’s Plant and Food colleague Shane Maley.
“The soil’s pretty much like flour.”
How compost changes that will be monitored, as will moisture retention and distribution of nutrients through the soil profile to 1.5m deep, something that is impossible on the South Canterbury site due to stony subsoil.
Tregurtha says poor structure as seen at Lincoln is not unusual: “Across the Canterbury Plains there are a lot of paddocks like this that could really benefit from the use of composts.”
However, as various speakers at the field day noted, the challenge is to get compost from processing sites near large towns such as Christchurch and Timaru, which supplied the Lincoln and South Canterbury trials respectively, applied on farm in sufficient volume to make a difference without blowing the budget.
Transpacific Industries, which runs the Timaru District Council composting site and is a 50:50 partner with Living Earth in Christchurch’s composting facility, says it is charging $30/t for its product ex-depot, with about 13t normally fitting in truck.
“We’re still doing work to get a realistic price based on its value, but we’ve got to be prepared to meet the market. The bug bear is it is so bulky,” says Transpacific’s organic processing planner Geoff Hemm.
For $30 buyers get $65-$70-worth of nutrient, but have to a pay a premium for spreading, he acknowledges.
Timaru’s green waste is being turned into about 8000t/year of clean, screened, weed-free compost by Transpacific while Christchurch generates about 70,000t though the potential is 100,000-120,000t says Living Earth’s George Fietje.
The Lincoln trial is funded by MAF Sustainable Farming Fund with composter Transpacific Industries, Canterbury Waste Joint Committee, Environment Canterbury, FAR and Ballance Agri-Nutrients.