Weed Control with Straw Residues in Occasional Direct Seeding of Faba Bean (Vicia faba sp.) in Organic Agriculture

In order to gain momentum in the consolidation process of no-tillage systems in Europe’s Organic Agriculture, occasional direct seeding (DS) of faba bean (FAB) into a mulch layer of residues from precrop oats should be scrutinized. In contrast to non-legumes, grain legumes do not depend on soil-borne nitrogen due to their ability to fix nitrogen symbiotically. Concerning weed infestation, straw residues left by precrops may at least physically suppress weeds. In order to prove this hypothesis, two field experiments were carried out in 2009 at two sites in the lower Rhineland region, Germany. DS treatments were combined with 0, 4, and 6 t ha-1 of straw residues. Mouldboard ploughing (MP) combined with conventional seedbed preparation was used as control. Compared to the DS treatment without straw residue (0 t ha-1), DS treatments with straw residues (4 and 6 t ha-1, resp.) resulted in significantly lower weed density (70 and 84 % resp.). Neither differences were observed in both shoot dry matter of FAB and weeds for DS with straw residues compared with MP, nor for the grain yields of FAB. We conclude that occasional DS of FAB in OA is successful to reduce annual weeds sufficiently and may not lead to reduced FAB yields

Kontrolle von Rumex spp. mit Citronella-Öl im Organischen Landbau

Citronella is an oil, extracted from lemon grass species (Cymbopogon sp) and has been identified as a potential burn-down bioherbicide. In greenhouse pot experiments two fractions of dock roots, Rumex obtusifolius and Rumex crispus (light root fraction, LW: 5-12 g root weight and heavy root fraction, HW: 15-30 g weight) were planted. 116 days after planting the mass of the untreated control gave an increase of 600% (LW) and 300% (HW) root mass, respectively. Citronella oil hindered the accumulation of assimilates in the roots showing a slight decrease of the initial root mass. Efficacy of citronella oil was higher as with cutting the leaves. Citronella oil also showed its efficacy to decrease the leaf area of dock plants after application of lower concentrations (12.5%, 25% and 50% of the recommended concentration), rather than their counterparts acetic acid and pelargonic acid