News & Media

By Jeffrey Carter – freelance journalist based in Dresden jcarter@ciaccess.com

A 10-year study at the Harrow research station has been looking at urban carbon sources.

There’s an opportunity for cities to help revitalize Canada’s agricultural soils by supplying composted organic materials – things like food scraps, leaf litter and lawn clippings.

Agriculture and Agri-Food Canada soil scientists say that by applying an organic carbon source, even once or twice every 10 years, there can be positive impacts. There are yield gains and, with improved soil structure, nutrients are more likely to stay put.

Dr. Dan Reynold, Dr. Craig Drury and other soil scientists at the AAFC research station at Harrow are just wrapping up a 10-year study looking at the potential of organic carbon source from cities and other places.

“As soil quality degrades, farmers have been able to compensate by adding more and better fertilizers. That has worked from a yield aspect, but from an environmental aspect, we’ve ended up with more erosion, more leaching losses of nutrients into the tiles, drainage water and groundwater,” Reynolds says.

“The algae blooms, particularly in Lake Erie, they’re caused primarily by agricultural runoff.”

Reynolds and Drury say farmers have helped alleviate environmental concerns through conservation tillage practices. Unfortunately these do not adequately address the basic problem of soil structure as it relates to soil carbon.

They cite a long-term comparison between no-till and moldboard plowing in continuous corn at Eugene F. Whelan Research Farm in Essex County as evidence. The no-till plots at the Brookston clay site do tend to have higher levels of organic carbon on the soil surface. However, when the carbon content in the entire topsoil profile is measured, carbon levels in the two treatments were about the same.

To understand the situation, Reynolds says farmers should consider the state of undisturbed woodlots soils that once dominated the area and compare them to today’s farm fields.

The latter are often grey in colour and, after a summer dry spell, cracks reach deep into the soil profile. They also tend to have a high bulk density – a compacted nature – that requires heavy equipment to break them up.

Left in their natural wooded state, these soils contain far more organic carbon. The water-hold capacity and air capacity are greater. From a visual standpoint, they have a dark colour and crumbly consistency.

For agricultural purposes, Reynolds says the ideal situation lies somewhere between the two extremes.

With organic carbon, the content should be from three to five percent by weight of agricultural purposes – the sweet zone. That compares to six to seven per cent for woodlot soil and around two percent for today’s typical Brookston-clay soils under a corn-soybean-wheat rotation.

Organic carbon is the carbon portion of organic matter. To calculate the amount of organic matter in soil from the organic carbon level, multiple by factor of 1.72.

The challenge is to return organic carbon source to the soil. Reynolds and his associates have found there can be long-term benefits from just a single application.

Five different materials were compared including 75, 150 and 300 tonnes of composted household vegetable waste per hectare, 75 tonnes of composted yard waste and a mixture of 75 tonnes of composted pig manure and straw. These were fall-applied to plots of continuous corn at the Whelan Research Farm in 1998. Over the next nine years, physical and biological changes to the soil were recorded along with yields and other data.

Both chemically fertilized and unfertilized plots were examined.

Reynolds says continuous corn was chosen for the experiment in an attempt to isolate the impact of the compost from other factors – such as the benefits that may have been derived from a crop rotation.

In both the chemically fertilized plots there were yield advantages associated with the addition of compost from all the sources, Reynolds and Drury say.

Over the first five years of the experiment on plots receiving chemical fertilizers, average yield advantages ranged from 12 per cent with the pig manure/straw compost combination to an 18 per cent advantage with the 300 tonnes of composted food waste.

Interestingly, the pig manure/straw compost came out on top over 10 years on chemically fertilized plots with an average yield advantage of 14 per cent. The smallest, average 10-year yield advantage associated with a compost application was five per cent.

In the plots that received no chemical fertilizers, the yield advantage associated with compost was often much greater in the first few years. However all yields in the unfertilized plots were relatively low compared to those receiving chemical fertilizers, regardless of the application of compost.

“The findings are encouraging,” Drury says.

“We can start engineering soils (using compost). We don’t have to wait 50 years for benefits of wider rotations to kick in.”

Reynolds feels yield benefits from compost in the fertilized continuous corn plots can be primarily linked to the improved physical characteristics of the soil. There were also positive biological changes and compost provides a source of slow-release nutrients.

The use of compost is often associated with organic production but there are others who see a benefit.

In Chatham-Kent, for instance, Carl Sterling has been using a mix of composted cattle manure, wheat straw, soybean straw and food waste on his 120-acre home farm outside Paincourt. After spreading 11 to 22 tonnes per hectare over four years, he says his organic matter levels have been increased from about six to seven per cent or better and the ground has more tithe.

Sterling hopes to reduce or even eliminate his use of fertilizer over time.

For farmers without an adequate source of cattle manure, municipal organic waste could provide an answer.

The Composting Council of Canada surveyed 227 centralized composting facilities across Canada. In 2005, these produced nearly 2.5 million tonnes of compost using nearly four million tonnes of feedstock.

Yard waste, wood waste and animal manure were the most common materials composted but residential and commercial food wastes were also utilized.

In comparison, back in the early 1990′s, less than 300,000 tonnes of organic materials composted by centralized facilities.

There’s room for further growth.

Danielle Buklis, a project coordinator with the council, says the amount of municipal organic waste being composted could be tripled.

The market price of compost varies widely. Some municipalities sell it in bulk for as little as $5 per tonne while privately operated facilities often charges $20 to $30.

Reynolds says it’s unlikely to be a cost-effective measure, based on the amount of nutrients release to the first crop after application. However, when long-term benefits are considered, applying compost to farmland may be an economically viable option.

Dr. Rob Nurse and the rest of the team at Harrow are embarking upon a new study involving compost as a mulch and soil amendment for vegetables grown on Harrow sandy loam soil.

This article was originally published in the June 30th, 2009 edition of the Ontario Farmer Magazine.