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Browsing by Subject "Mixtures"

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    Evaluating different management strategies to increase the effectiveness of winter cover crops as an integrated weed management measure
    (2020) Schappert, Alexandra; Gerhards, Roland
    Weed control in agricultural production systems is indispensable to achieve stable crop yields. Integrated cropping systems are demanding for preventive and ecologically harmless weed control measures in order to protect soil and water resources and to retard the selection of herbicide-resistant weeds. Well-established winter cover crops provide nutrient retention and soil protection and may effectively suppress weeds. This contributes to reduce chemical and mechanical fall- and spring-applied weed control practices. However, producers are cautious towards integrating cover crops in crop rotations, as their performance is related to environmental conditions and varies, therefore, significantly from season to season. To increase their integration into cropping systems, reliability on weed control by cover crops needs to improve. In the current study, management strategies such as i) the cover crop sowing method, ii) the selection of water deficit tolerating cover crop species, iii) cover crop species combinations, iv) the adjustment of the mulching date and v) tillage practices after cover crop cultivation were considered as possibilities to improve the effectiveness of cover crops to control weeds during cultivation and in the subsequent cash crop. Within the first and the second publication, the general weed and A. myosuroides control ability of a cover crops mixture during and after cultivation were compared in the field with various fall-applied tillage methods and glyphosate treatments. Due to the development of highly competitive cover crop stands, weeds were suppressed by 98% and A. myosuroides by 100% during cultivation. Therefore, cover crops were more efficient compared to glyphosate application(s), non-inversion and inversion tillage and revealed a great potential to reduce or even replace chemical and mechanical fall-applied weed control measures. The efficient A. myosuroides control during the cover crop cultivation remained until spring barley harvest. This quantifies cover crops to complement herbicide resistance management strategies. In contrast, due to the weak cover crop performance during fall-to-winter within another two experiments included in the second article, weed suppressive effects of cover crops disappeared after the cultivation of cover crops. This might have been the reason why reduced tillage and adjusted mulching dates in spring failed in contributing to expand weed suppressive effects of cover crops in these experiments. Cover crop mixtures are attributed to show a greater resilience against unfavorable conditions than pure cover crop stands which is expected to result in an increased weed suppression ability. Within article three, the weed control efficacy of pure cover crop stands was compared with species mixtures. Pure stands of Avena strigosa Schreb. and Raphanus sativus var. oleiformis Pers. provided the most efficient weed control with 83% and 72%, respectively. Cover crop species mixtures showed a weaker weed suppression ability than the most efficient pure stand. In order to improve the weed control ability of cover crop mixtures, it was evaluated that the species selection is more relevant than the species diversity. Thereby, environmental requirements, such as water and temperature demand, and weed suppression mechanisms should be considered. Weed suppression of mixtures was improved by increasing the proportions of A. strigosa and R. sativus var. oleiformis, as they were showing a susceptibility for dry conditions and combine a strong competition for resources and allelopathic interference with weeds. Within the fourth article, it was explored whether a low susceptibility of single cover crop species to water-limitations accompanies an improved weed suppression ability. A. strigosa and Sinapis alba L. showed differing suitabilities to cope with water-deficit in the greenhouse. A relation between weed suppression and water demand of cover crops at the field was not identified. Although the weed control ability of cover crops is generally narrowed under water-limited conditions, the weed suppression potential of individual species seems to be independent of their water supply. The adjustment of the cover crop sowing method, the consideration of species-specific requirements and the mixing strategies, were evaluated as being important to improve the resilience of cover crops against severe environmental conditions and their weed control ability. Investigations of cover crop mixtures with respect to single component species, their mixing ratios and seed densities, might further increase the absolute and average effectiveness of cover crops as an integrated weed management practice.