Inside View: Organics: Feed the soil and not the plant

April 30, 2009
Written by Gary Jones
When we look at growing media, most of us in greenhouse production start thinking of pH, EC, nutrient content, and water holding capacity, among other things. Nothing wrong there. We consider the medium as something to provide support to plants, help provide nutrition, and regulate water and oxygen availability to roots. Oh, and if it’s a proprietary mix or bulk raw materials, “growbag” or inert slab, of course we think about the cost.

But what about its effect on and contribution to the bigger picture – climate chaos and greenhouse gas emissions? Work reported at this year’s Guelph Organic Conference provides a whole new world of information about the “dirty side” of our business.

Derek Lynch, Canadian Research Chair for Organic Agriculture based at the Organic Agriculture Centre of Canada (OACC), looked at management practices of agricultural systems and how this affects greenhouse gas (GHG) emissions. Oxides of nitrogen (NOx) are greenhouse gases that can be readily measured from soil systems, and provide an opportunity to estimate if organic production is better for the climate than conventional systems.

Lynch and his colleagues found that the type of manure and other off-farm amendments, such as composted waste paper and composted municipal wastes, affect the level of (NOx) emissions from soil. Using green manure and paper compost reduces GHG emissions by 37 per cent and 57 per cent, respectively, compared to a conventionally fertilized crop. While not new information, they also corroborated that plowing and other soil work generally release GHGs into the atmosphere. Interestingly, clover grown as the green manure source of nitrogen for potato crops reduces GHG emissions by up to 60 per cent, while potato yields were maintained at acceptable levels (about 30 t/ha).

Tek Sapkota, from the University of Pisa, Italy, also looked at organic systems and their effects on climate change. He and his colleagues reminded delegates that climate change leads to drought, floods, potentially more pests, and an increase in average sea level. Agriculture is responsible for 13.5 per cent of all of mankind’s GHG emissions. However, the choice of growing systems can reduce GHGs and, furthermore, sequester carbon through different agricultural practices, so it’s certainly possible to mitigate our negative effects with positive ones and come out with a better net balance. After all, we all need to eat, so stopping agriculture is not an option!

In general, organic agriculture can reduce CO2 output, increase carbon sequestration and consume less fossil fuels per kilogram biomass produced than conventional agricultural systems.

In his project, Sapkota compared conventional and organic field cropping systems for five years starting in June 2001. He calculated total CO2 outputs from a number of sources: fer-tilizer manufacturing and inputs, pesticide use and fossil fuels used in both systems. Organic systems came out well ahead; that is, they were producing fewer GHGs. Organic systems were also found to increase the amount of carbon put into the system (e.g., through use of composts or manure). There are net benefits to adding carbon to the soil and reducing the carbon lost to the air, and therefore an overall improvement on carbon balance.

Furthermore, because of the fossil fuels used, energy input into conventional systems is much higher than organic systems, and biomass production per kilogram fuel input is significantly higher in organic systems.

Andy Hammermeister and a colleague, also from the OACC, reported on a survey that had been distributed among more than 830 organic producers and industry affiliates. Among other outcomes, respondents identified the following major research needs with respect to growing media:

Soil fertility and crop nutrition, especially crop rotations and soil biology.

Ecology and environment, especially biodiversity, soil quality, reduced pesticide inputs, and reduced energy systems.

When it comes to growing media and crop nutrition, one of the most basic principles of organic production has been to “feed the soil, not the plant.” In the framework of the bigger global picture, this is an approach that clearly has a lot going for it.

Gary Jones is Chair of Production Horticulture at Kwantlen University, Langley, B.C. He sits on several industry committees and would welcome comments at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

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