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Organic Agriculture Centre of Canada

Organic farmers can鈥檛 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 鈥渉ow important green manures and other crop rotation practices are to organic farmers for soil fertility and soil and weed management,鈥� 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. 鈥淚t has a number of benefits,鈥� says Alison Nelson, lead author of 鈥溾��.

鈥淚f it鈥檚 a legume it fixes nitrogen which is added back into the soil,鈥� said Nelson.

鈥淎nd it adds all that organic matter back to the soil. The farmers I鈥檝e talked to and worked with tend to plow it under partway through the season.鈥�
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The study found that twice as many organic farmers had row crops in rotation compared with conventional farmers. This may indicate that organic farmers are substituting row crops for solid-seeded crops. 鈥淚f this is true, a reduction in the amount of stored organic C (carbon) is expected since row crops generally have lower residue levels and require more tillage than solid-seeded crops,鈥� states the report.

Nelson said carbon storage is lower because there is generally less biomass with row crops, such as potatoes, compared with field crops. 鈥淩ow crops can be tilled during the growing season, so those extra tilling operations can break down organic matter quicker,鈥� said Nelson. 鈥淭hey鈥檙e not as good for building up stored organic carbon.鈥�

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. 鈥淗aving livestock on the farm makes the most sense, because you鈥檙e not taking that crop off the farm and transporting it somewhere else,鈥� 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. 鈥淎 lot of forages are perennial, so they鈥檒l be deeper rooted and they help build soil structure and organic matter,鈥� 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 funds. 听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. 鈥淪o you鈥檙e not actually tilling it under,鈥� said Nelson. 鈥淵ou鈥檙e keeping it rooted in the soil and the organic matter is staying on the surface and protecting the soil crop from erosion.鈥�

Different practices used by organic farmers to manage their soil and crops have a common theme. 鈥淭he idea with an organic system is to try and prevent problems from occurring,鈥� said Nelson.

This article was written by Steve Harder on behalf of the OACC with funding provided by Canada鈥檚 Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).听 The Organic Science Cluster is a collaborative effort led jointly by the OACC, the and industry partners. For more information: oacc@dal.ca or 902-893-7256.

Posted August 2010