If farmers want to use reduced tillage in organic agriculture, they often face great challenges in weed control. One goal of the European research project TILMAN ORG (www.tilman-org.net) was to develop a more efficient weed management and increased biodiversity through improved use of green manures in different systems of reduced tillage.
In a repeated one year trial on the research farm of University of Kassel the effects of different green manure species and different tillage systems on weed cover, density and biomass as well as yield of a subsequent main crop were examined. Sinapis alba, Trifolium resupinatum and Vicia sativa were tested as green manure species. Bare fallow served as control. After the green manures the main crop oat was sown in four different tillage systems: (1) plough, (2) chisel (2011/12) or disc harrow (2012/13), (3) mulching + drilling and (4) direct drilling.
In 2011/12, weed cover was generally low in the plough system compared to the other tillage systems. In the mulching + drilling- and direct drilling- systems V. sativa was able to suppress weeds considerably more efficiently than the other green manure treatments. The oat plots after the green manure species S. alba and T. resupinatum as well as the bare fallow had to be given up because weed pressure was too high. Instead, the oat yield in the mulching + drilling- and direct drilling treatments after green manure species V. sativa resulted in oat yields similar to the plough treatments. In the chisel system, oat yield in the V. sativa treatment was significantly higher than in the other green manure treatments. 2012/13 all mulching + drilling- and direct drilling- plots had to be given up because of too high weed pressure. In the disc harrow– system weed pressure differed not significantly from the plough system, but only green manure species V. sativa resulted in comparable oat yields
