Reduced tillage in organic cropping systems on the Canadian prairies
Organic producers on the Canadian prairies rely heavily on tillage for weed control and soil nutrient management. Intensive tillage degrades soil quality, and therefore efforts to reduce tillage in organic agriculture are increasing. Research has focused on replacing tillage for green manure termination with alternative low-disturbance methods. The roller-crimper terminates green manures by rolling over the crop and creating a mulch that is anchored to the ground. Rolled mulches can suppress weeds and conserve soil moisture, but surface-placed residues can delay N mineralization and result in subsequent yield loss. Three field studies were conducted in Saskatchewan, Alberta and Manitoba using the roller-crimper to determine the extent to which tillage can be reduced in organic systems without negatively impacting nutrient availability and yield. At two sites in Saskatchewan, the effects of termination timing (early flower, late flower, early pod) and termination method (rolling, mowing, tillage) of field pea (Pisum sativum) and faba bean (Vicia faba) green manures on soil properties and spring wheat (Triticum aestivum) performance were measured in 2009 and 2010. Faba bean did not establish well and failed as a green manure crop. Termination timing and method affected soil properties in the first year, but did not affect wheat yield significantly. Wheat yield was equivalent in the rolled and mowed treatments to the tilled treatment, indicating field pea termination without incorporation does not inhibit wheat yield under moist conditions. Soil inorganic N was measured in the spring of 2011 following green manure (field pea/barley [Hordeum vulgare]) termination in 2010 by tillage, rolling, rolling + fall tillage, and mowing at two locations. Inorganic N was highest in the tilled plots at both sites, but effects on 4 wk mineralized N (Nmin) differed between sites. When the green manure C:N was narrow (14:1), tillage resulted in lower Nmin than the other treatments; when the C:N was wider (20:1), tillage resulted in the highest Nmin. These results confirm mineralization rates vary with residue placement and N content. Lastly, the effect of 2 yr of continuous no-tillage (NT) or conventional tillage on available N and P, soil microbial biomass (SMB), and oat (Avena sativa) N and P uptake was measured at one site in 2010. Overall, tillage regime did not affect N and P availability, SMB, or oat nutrient uptake. Microbial biomass C and inorganic N tended to be higher in the NT treatment at 0 to 5 cm, suggesting differences may become apparent in the long term. This research confirms that a reduction in tillage is possible in organic systems on the Canadian prairies. The degree of reduction is dependent on the green manure used, soil and climatic factors, and the goals of the producer.
DegreeMaster of Science (M.Sc.)
DepartmentGraduate Studies and Research
SupervisorKnight, Joan D.
CommitteeSchoenau, Jeff J.; Pennock, Dan J.; Walley, Fran L.
Copyright DateFebruary 2012
green manure termination
soil inorganic N
soil microbial biomass