Flax (Linum usitatissimum L.) production system performance under organic rotational no-till and two organic tilled systems in a cool subhumid continental climate

Abstract

Studies comparing crop agronomic response in organic production systems under contrasting tillage practices are lacking. The objective of the study was to compare the effect of organic rotational no-till and two organic tilled systems on the basis of mulch biomass, soil chemical properties, weed control, and subsequent crop productivity. A field study consisting of two-year sequences was conducted three times at three close sites in Carman, Manitoba, Canada (2009–2010 at site A, 2010–2011 at site B, and 2011–2012 at site C), on Chernozem soils. Three management systems of cover crops were tested, in a randomized complete block design. A barley (Hordeum vulgare L.)/hairy vetch (Vicia villosa Roth) cover crop was grown in the first year of the study and terminated by rolling (no-till), rolling and tillage (Roll+Till), or haying and tillage (Hay+Till). Flax (Linum usitatissimum L.) was seeded the following year. Our first hypothesis that a full-year growth of barley/hairy vetch cover crop allows the production of between 6 and 8Mgha−1 of mulch biomass for the subsequent crop was confirmed in two of three years. Flax was no-till seeded into 6.7, 7.7, and 4.2Mgha−1 of mulch at sites A, B, and C, respectively. At two of three sites, flax seed yields were significantly higher in no-till than in the two tillage treatments. There was no penalty on flax seed yield for haying the cover crop in mid-summer instead of incorporating it into the soil by tillage, across all three sites. There was an overall trend towards lower contents of soil nitrate-N in no-till, although it did not greatly influence total plant nitrogen uptake at two of three sites. This corroborates our second hypothesis that while flax N uptake would be reduced by the reduced soil N status in no-till, there will be sufficient N for optimum flax yield. The third hypothesis that barley/hairy vetch cover crop mulches have the ability to provide adequate weed control was generally supported, though there were important exceptions when insufficient mulch biomass was produced. Success of flax crop grown in an organic rotational no-till system in southern Manitoba depended on weather, mulch biomass production (>6.7Mgha−1), and weed species present. The fourth hypothesis that there is no yield penalty for eliminating tillage for 1.5 years in an organic flax crop in southern Manitoba held true only if that minimum mulch biomass benchmark of 6.7Mg ha−1 was reached.