Reducing rubbish by feeding the soil

Research has shown that everyday kitchen scraps and garden waste can be used to increase the production of farmers’ crops and reduce their need for conventional fertilisers.

A trial by Plant & Food Research showed that adding compost to different farming scenarios increased the production of arable crops by up to 14% and forage crops by up to 50%. This compost, made from municipal garden and food waste, increases the health of soil, resulting in a better crop yield and reduced need for nitrogen fertilisers, as well as redirecting waste that may otherwise enter landfills.

The research has been used to develop guidelines for farmers in the Canterbury area, where municipal composting schemes use around 50,000 tonnes of green waste to make 25,000 tonnes of compost each year.

“Plants need nitrogen and other nutrients to grow,” says Plant & Food Research scientist Abie Horrocks. “These nutrients and high levels of carbon are present in compost and adding it to soil boosts production. Because it can also supply the plants with nitrogen, a reduction in nitrogen fertiliser application is also possible without compromising yields.

“Around 726,000 tonnes of garden and kitchen waste is buried in New Zealand landfills each year. The proximity of farms to the source of municipal compost will strongly influence the profitability of utilising compost in agriculture. This research suggests that agricultural sectors close to populated areas, where municipal composting facilities could be developed, would benefit most from using compost and could result in redirecting most, if not all, the green waste for profitable use.”

The 3-year field trial assessed the effects of different rates of mature municipal compost (0, 25, 50 t/ha) in combination with different rates of nitrogen fertiliser (urea at 0, 33, 67, and 100% of standard rate) on crop production. Productivity was then compared to standard practice (100% crop-model-recommended fertiliser nitrogen and no compost).

By adding compost and reducing nitrogen fertiliser by one-third the recommended rate, arable crops were shown to yield 10% greater than standard practice. Applying compost without reducing nitrogen fertiliser resulted in productivity increases of 14% over the three year cropping rotation. When used in the production of forage crops, yield increases of close to 50% were achieved compared to where no compost was applied.

The research was conducted with funding from the Sustainable Farming Fund and with support from Transpacific Industries, Canterbury Waste Joint Committee, Environment Canterbury, Ballance Agri-Nutrients, Living Earth, Timaru District Council, Poulfert, the Foundation for Arable Research and the Ministry for the Environment.