Weed manifestation under different tillage and legume undersowing in organic wheat

Abstract

Field experiments from October 2010 to August 2012 were conducted at the Royal Agricultural University's organic Harnhill Manor Farm near Cirencester, UK to explore tillage and legume undersowing effects on dry matter (DM) of broadleaf and grass weed infestation in organic winter and spring wheat. The experiments were designed using a randomized complete block with split plot arrangements. Tillage treatments involved conventional tillage (CT), low residue non-inversion tillage (LRNiT) and high residue non-inversion tillage (HRNiT) as main plots with undersowing white clover (WC), black medic (BM) or non-undersown (Nus) as subplots. In both cropping seasons, among tillage treatments, HRNiT had significantly higher total weed DM than CT or LRNiT. The mid-season assessments for weed species indicated HRNiT as having significantly higher grass weed DM than CT or LRNiT for both the wheat types. Broadleaf weed DM was significantly higher under CT than under LRNiT or HRNiT for winter wheat after GS61, whereas for spring wheat, broadleaf weed DM was significantly higher under CT than under HRNiT throughout the growing season. Undersowing had a significant effect only in spring wheat. Among undersowing treatments, WC had significantly lower total weed DM than BM. The broadleaf weed DM was significantly lower under WC than under BM or Nus. On the basis of these results, increasing the levels of tillage intensity with complete (0%) or minimal (30%) dispersion of soil cover appears to have decreased grass weed and total weed DM. Among undersowing treatments, WC seems to be a more reliable option than BM for spring wheat.