Researchers show soil microbes increase in organic fields -
Timing of cover crop planting is important to good performance, depending on variety

By Jeffrey Carter, Special to Ontario Farmer
Tuesday, February 7, 2006

Prince Edward Island organic potato growers have had good luck using shellfish waste as a nutrient source and disease control agent.

Greg Peters of the Agriculture and Agri-Food Canada research station at Charlottetown has been investigating the practice. Peters, and other researchers, had an opportunity to talk about their work, at the Guelph Organic Conference in January.

"In terms of yield, we get just as a high a yield with the raw shellfish waste as with commercial fertilizer and we're also boosting soil calcium," Peters says. Peters says the practice is also having a positive benefit on soil microbial life. Beneficial bacteria are providing disease control in the soil and are also being taken up by the tubers, enhancing their storage capability, Peters says.

"In a sense, we're creating these tubers that have these bio-control agents built into them. I'm quite excited about this."

The raw shellfish waste, which is simply spread on the field, seems to work better than if it's composted, Peters says. With a nitrogen content of two to four per cent, it provides a similar nitrogen boost as commercial fertilizer.

Another East Coast researcher, Derek Lynch of the Nova Scotia Agricultural College, talked about an Ontario study of 15 organic dairy farms.

Working with a team of researchers, Lynch has been looking at the environmental nutrient impact of 15 organic dairy farms as compared to conventional dairy farms.

The 15 farms, all under organic management for 10 years or more, are located in western and eastern Ontario. The average farm size is 110 hectares. The average herd composed of 52 milking cows producing, on average, about 8,200 kilograms of milk annually - somewhat lower than the overall Ontario average.

The biggest crops grown on the farms include forage and pasture and small grains. On average, less than six per cent of the acreage was composed of corn and half the farms didn't grow any corn.

Soil organic levels were around 4.8 per cent.

It was found that the farms were not in a significant nutrient surplus position. In comparison, many intensive, confinement dairy operations have a far greater nutrient surplus.

One concern for the organic farms is the long-term maintenance of available soil phosphorus.

SOIL phosphorus levels on organic farmers have also been the focus for Cathy Welsh who's working with Dr. Mario Tenuta at the University of Manitoba. Rotational research at the university's Glenlea Farm has shown that while available phosphorus levels may be lower with organic practices, overall phosphorus levels - both available and unavailable - are similar to conventional farms.

"With the addition of animal manure, you may increase the level of available phosphorus," Welsh says.

It's also been found that organic systems support a greater population of arbuscular mychorrhizae, fungi that support the plant uptake of phosphorus. Consequently, while organic soils may have lower levels of phosphorus, the activity of this fungi may enable plants to better utilize what's there.

Unfortunately, canola, members of the crucifer family do not use these soil-borne helpers.

Organic methods also improve soil structure and increase the level of microbial activity, Welsh says.

SOILS scientist Paul Voroney of the University of Guelph has been looking at the impact of organic methods over the past three or four years. Using adjacent fields in nine different locations, he's compared the impact of conventional practices with organic practices.

On average, organic matter levels were 15 per cent higher in the organically-managed fields. There were also better soil structure and a 20 per cent increase in the number of living soil microbes in the top 10 centimetres of the soil profile. The number of earthworms in organic and conventionally-managed soils were similar, Voroney says. Conventional farms tend to use less tillage which may account for their competitive numbers.

DR. ANN CLARK of the University of Guelph provided a broad view of organic agriculture as she tackled the subject of ecological sustainability. In this context, organic agriculture may not be much further ahead than conventional agriculture, she says.

"Organic agriculture is not sustainable by design," Clark concludes.

"If we truly wish to be sustainable, we need to come up with a new design."

Clark has developed a system to rank agricultural systems for their sustainability. More points are given to systems that retain nutrients, nurture a wide spectrum of plant types including perennials, have a minimum amount of bare soil exposed, include a livestock component, and involve local or regional marketing.

Clark also discussed the use of cover crops or "system service crops" in organic agriculture. Research at the Ignatius Jesuit Centre outside Guelph showed that buckwheat, oilseed radish and sorghum Sudan grass performs well when established in the summer. Legumes such as red and sweet clover would perform better if they're under-seeded in the spring.

Clark was somewhat surprised at the performance of sorghum Sudan grass which provides a huge amount of biomass for plow down and suppresses weeds.

OACC gratefully acknowledges Ontario Farmer for permission to post this article on our website.