Cover crops are one of the best ways to improve soil health, maintains a long-time organic vegetable grower from Nova Scotia.
David Blanchard was one of the keynote speakers at the 2016 Soil Sessions staged recently by the PEI Certified Organic Producers Cooperative. The two day session attracted over 40 participants. Sandy MacKay said they included both organic and conventional growers and varied in size from an acre and a half to over 500 acres.
"Sessions like these are a great opportunity to not only learn from the speakers but to learn from each other," MacKay said.
Blanchard operates Pleasant Hill Farm and has over 40 years of experience in the industry. He was also involved in developing the online cover crops tool in Nova Scotia. Blanchard told the meeting soil health essentially means the ability to support crop growth without becoming degraded.
Blanchard said a holistic approach is needed to soil health encompassing biology (how the living organisms in the soil interact with each other ), chemistry (the nitrate and pH levels) and physics (soil composition and water retention capacity). Blanchard noted the rising world population and the impacts of climate change are two major reasons why soil health now matters more than at any other time in history.
"There is no single cover crop that can provide an optimum outcome," he told the meeting.
However, he said a mixture of cover crops can help prevent erosion by water and wind. Blanchard added "the soil lost to erosion typically contains three times as many plant nutrients as the soil left behind and it also results in significant loss of the water holding capacity."
The guest speaker noted cover crops reduce run-off by slowing down the flow of water across a soil surface. Blanchard pointed to a ten year study south of the border which showed using rye as a cover crop reduced soil run-off by 43 per cent.
As well, he said cover crops play a role in scavenging nutrients and preventing leaching. Blanchard noted soil run-off into rivers is often considered by organic growers to be a problem largely for the conventional sector, but he warned the over-application of organic amendments can lead to nitrogen leaching.
"Cash crops can also be important to building and maintaining soil organic matter," he said. "It you want to control the nitrogen from your cash crop, grow a grass crop."
Blanchard said cover crops can be used to make a crop rotation plan even better. He noted research has shown adding a second cover crop in monoculture increases soil carbon by 2.9 per cent and "if the second crop is a cover crop, soil carbon increases 7.5 per cent."
"Cover crops improve soil structure and lead to better water infiltration and less run-off because water is available for the crop," he pointed out. "There is better gas exchange (oxygen in and carbon dioxide out) and less tillage is needed."
As well, he said a cover crop can help suppress weeds, adding "a dense fast growing cover crop can out-compete weeds. As well, he said some cover crops also excrete a substance that can help suppress weed growth.
Blanchard said cover crops can loosen soil compaction, recommending root crops for deep compaction. Flowering cover crops can also help build the population of native pollinators.