Organic agriculture offers helpful options to manage nutrients

By TANYA BROUWERS
It is a well-known fact that nutrient leaching from intensive agricultural activities is a major contributor to the pollution of Canada's limited and, therefore, precious groundwater supply. The consequences of this widespread, and largely unchecked contamination are numerous; domestic wells tainted with nitrates have been linked to health concerns in pregnant women and infants; where the affected water is discharged into surface bodies like streams and wetlands there is an increased incidence of reproductive disorders in fish and other aquatic life; oceans, too, are at risk when agriculturally polluted rivers become the fuel for algae blooms and the resultant 'Dead Zones'. In a country such as ours, where population pressures already threaten the viability of underground water sources and where marine ecosystems are fragile, the promotion of agricultural practices that minimize nutrient loss are becoming higher priorities of farmers and the federal government alike.
In response, Dr. Derek Lynch of the Nova Scotia Agricultural College has published a paper, "The Environmental Impacts of Organic Agriculture: A Canadian Perspective", a section of which addresses the positive role of Canadian and North American organic farming practices to reduce off-farm nutrient losses. The cited studies comparing nutrient leaching on both organic and conventional farms are, Lynch admits, by no means exhaustive, but they are a vital first step in creating a compelling body of North American based research, largely lacking up to this point, that should influence Canadian agricultural and environmental policy makers.
In his paper, Lynch stresses that the use of green manures in organic crop rotations appear to have a mitigating affect on the nutrient levels in agricultural soils. He notes that legumes, especially, will act as a "buffer", moderating nitrogen levels in the soil and, by reducing the need for additional organic amendments, will also minimize soil accumulation of phosphorous and potassium.
Interested parties in Eastern Canada, where an increasing acreage of agricultural soils have been classified as a source of nitrate losses to water, should especially take note of Lynch's conclusions. He cites two studies in both Prince Edward Island and New Brunswick that compare the residual soil nitrates (RSN) in commercial organic and conventional potato operations following potato harvest. Both studies concluded that RSNs were markedly lower in the organically managed systems where legume plowdowns were utilized as the nitrogen source. Similarly, a study from Washington State, comparing the annual nitrate leaching in conventional and organically managed orchard systems concluded that the nitrate leaching in conventional orchards was 4.5 to 5.6 times greater than that in the organic orchard.
Nutrient losses to air, soil and water are also affected by the type of livestock management system. Organically managed livestock farms, strictly adhering to the guidelines as outlined in the new Canadian Organic Standard, exhibit a much lower risk of off-farm nutrient loss than the more intensively managed, confinement based conventional operations. Lynch cites a 15-year study comparing the farm nutrient loading and loss on both organic and conventional dairy operations in Ontario. The study concluded that the off-farm nutrient loss was greatly reduced in the organically managed operation. A similar Canadian study by Martin and others (2007) comparing levels of labile soil phosphorous on organic and conventional dairies found that nearly all of the organic dairies exhibited lower levels of such phosphorous. Incidentally, phosphorous from agricultural run-off is one of the nutrients responsible for algal blooms in aquatic environments.
Citing a study by MacRae and others (2007), Derek Lynch notes that, "it is well established that the off-farm costs of mitigating soil and water degradation far exceed the costs of appropriate soil conservation and nutrient management practices on-farm." In light of the developing environmental and, consequently, economic benefits of organic agriculture, Canada's policy makers have new data to consider when assessing legislation and financial incentives for farming practices in a healthy future. Fortunately, Canadian researchers like Derek Lynch are taking the steps necessary to ensure that the North American based evidence pertaining to organic agricultural methods is compiled in a conclusive and reliable manner. Thus, it will be available to those individuals involved in Canada's agricultural industry that desire to improve agricultural resilience and stability. Given the increasing attention to the role of agriculture with respect to the health of Canadian people and our landscape, this research offers positive options for all farmers.
(Tanya Brouwers is a Consultant for the Organic Agriculture Centre of Canada. Please send comments or questions by phone to 902-893-7256 or by email to oacc@nsac.ca. One month after publication, OACC newspaper articles are archived at www.oacc.info. )