Intensive tillage by means of mouldboard ploughing can be highly effective for weed control in organic farming, but it also carries an elevated risk for rapid humus decomposition and soil erosion. Conservation tillage techniques offer considerably reduced soil erosion and improved soil structure but they are rarely used in organic farming systems due to the increased weed pressure. To develop organic systems that are less dependent on tillage this study evaluated the non-legume cover crops spring rye (Secale cereale L.), black oat (Avena sativa L.), sunflower (Helianthus annuus L.), white mustard (Sinapis alba L.), buckwheat (Fagopyrum esculentum Moench) and hemp (Cannabis sativa L.) for their ability to suppress weed growth, reduce plant available nitrogen in the soil and produce large amounts of biomass with slow N mineralisation, without and with the incorporation of organic fertiliser (horn grist, 50 kg N ha-1) before seeding. Resulting from these preliminary trials the spring rye was chosen as cover crop before no-till, reduced tillage and plough tillage cropping of legume cash crops monocropped and intercropped with cereal grains. The legume cash crops winter and spring faba bean (Vicia faba L.), field pea (Pisum sativum L.) and spring narrow-leafed lupin (Lupinus angustifolius L.), monocropped and intercropped with winter wheat (Triticum aestivum L.; winter crops) and oats (Avena sativa L.; spring crops) were evaluated for their dry matter production and grain yield as well as for their ability to suppress weeds. An additional study determined if the transition to the no-till system could be carried out through no-till seeding of summer annual legume cover crops faba bean, normal leafed field pea, narrow-leafed lupin, grass pea (Lathyrus sativus L.), and common vetch (Vicia sativa L.) monocropped and intercropped with sunflower after the harvest of cereal grain cash crops. The objectives of the studies were: (i) to examine six non-legume cover crops (rye, oats, sunflower, mustard, buckwheat and hemp) for their suitability for cover cropping preceding no-till sown legume cash crops through evaluation of their ability to produce biomass and reduce plant available inorganic soil N resources by N accumulation and assessment of long term N immobilisation in plant compartments with a high C : N ratio through simulated N mineralisation, (ii) to determine if the total biomass production and N accumulation can be increased by incorporating organic fertiliser before seeding, (iii) to assess the suitability of three different legume species (field pea, faba bean and narrow-leafed lupin) for no-till cash crop systems by examination of their grain production after no-till, reduced tillage and plough tillage, (iv) to determine the capacity of intercropped plant stands of legume cash crops and cereal grains to enhance the weed suppression and the total grain yield, (v) to investigate if autumn seeding compared to spring seeding of grain legumes can enhance the weed competition of legume cash crops, (vi) to determine if the transition to the no-till system can be alternatively realised through no-till seeding of legume cover crops or if tillage is needed for sufficient weed suppression and cover crop production.
The non-legume cover crop biomass production ranged from 0.95 to 7.73 Mg ha-1, with fertiliser increasing the total biomass at locations with low N status. Sunflower consistently displayed large biomass and N accumulation at all locations and fertiliser variations, although not always significantly more than other species. Most shoot-N was stored in sunflower leaf material, which can be easily mineralised making it less suited as cover crop before no-till sown spring grain legumes. Rye, which produced slightly less biomass, but accumulated more N in the stem biomass, would be better suited than sunflower in this type of ... | data is too long for this filed (Max of 4000 chars)