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Organic Agriculture Centre of Canada
Organic farmers can’t rely on synthetic pesticides and fertilizers for their soil management and crop production problems, so they need other options.
Green manures, row crops and forage crops in rotation and tilled summerfallow were significantly more common among organic farmers than conventional ones, a study has found.
The study, based on a mail-out survey of organic and conventional farmers with most of the responses coming from the Prairies, described land management practices affecting soil erosion risk.
The difference in approaches was most striking in growing green manures, with 84% of organic farmers doing so, compared with only 6% of conventional farmers. This illustrates “how important green manures and other crop rotation practices are to organic farmers for soil fertility and soil and weed management,” states the study.
The study said tilled summerfallow could increase soil erosion risk even when green manures are used during the fallow year. More research is needed to determine best management practices for reduced erosion risk.
Green manures are crops, such as sweetclover and buckwheat, grown for the purpose of being plowed under. “It has a number of benefits,” says Alison Nelson, lead author of “Organic and conventional field crop soil and land management practices in Canada”.
“If it’s a legume it fixes nitrogen which is added back into the soil,” said Nelson.
“And it adds all that organic matter back to the soil. The farmers I’ve talked to and worked with tend to plow it under partway through the season.”
Nelson said carbon storage is lower because there is generally less biomass with row crops, such as potatoes, compared with field crops. “Row crops can be tilled during the growing season, so those extra tilling operations can break down organic matter quicker,” said Nelson. “They’re not as good for building up stored organic carbon.”
Wide rows are often used to make weeding easier, but the increased tillage can lead to more erosion. There is also less soil coverage, compared with solid-seeded crops.
Forage crops were used by about two-thirds of organic farmers, compared with less than half of conventional farmers.
Forage crops, such as alfalfa, grasses and red clover, are grown to feed animals. “Having livestock on the farm makes the most sense, because you’re not taking that crop off the farm and transporting it somewhere else,” said Nelson.
Forage crops are generally harvested while the crop is still green. So there can be weed control benefits to that since weeds can have a more difficult time getting established. “A lot of forages are perennial, so they’ll be deeper rooted and they help build soil structure and organic matter,” said Nelson.
The study found that 52% of organic farmers used tilled summerfallow, compared with 6% for conventional farmers. Tilled summerfallow represents a risk to soil sustainability on organic farms.
Soil erosion risk can increase with summerfallow, even when green manures are used. The study recommended that future research should focus on reduced tillage systems for managing fallow periods.
Nelson described a system currently being tested by Dr. Martin Entz and others with Organic Science Cluster funds. A crimper-roller attached to the tractor can kill a green manure, but leave it as mulch on the surface. Then another crop can be sown directly into the mulched crop. “So you’re not actually tilling it under,” said Nelson. “You’re keeping it rooted in the soil and the organic matter is staying on the surface and protecting the soil crop from erosion.”
Different practices used by organic farmers to manage their soil and crops have a common theme. “The idea with an organic system is to try and prevent problems from occurring,” said Nelson.
See the research abstract...
© 2012, Organic Agriculture Centre of Canada (OACC)