Browsing by Subject "Cover crop"

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Cover cropping in integrated weed management
(2018) Sturm, Dominic; Gerhards, Roland
Weed control constitutes a major challenge in the worldwide crop production. Beside chemical and mechanical weed control strategies, cover cropping provides an effective way of biological weed suppression. Five different field experiments were conducted at six locations from 2014-2016 to evaluate the weed control efficacy of different cover crops in mono and mixed cultivation combined with different fertilization strategies and sowing dates. Furthermore weed suppressing effects of cover crop mulches in spring and of living mulches in summer were investigated. Potential effects on sugar beet emergence, quality and quantity were also assessed. In three laboratory and two greenhouse experiments from 2015-2017, the proportional contribution of competitive and biochemical effects on the overall weed suppression and the identification of varying susceptibilities of different weeds against biochemical stresses were at the center of research. In field experiments, the weed suppressive effects of cover crops and living mulches in mono and mixed cultivation were tested. The experiments emphasized the importance of cover crop and living mulch mixtures compared to mono cropping due to a higher flexibility to biotic and abiotic stresses. This was followed by a more constant biomass production and more effective weed suppression. Moreover, the observed weed control was a result of competitive and biochemical effects, induced by cover crops. These were later on analyzed for active weed growth suppressing compounds. Altering cover crop sowing date and fertilization to optimize the weed control resulted in significant changes of cover crop and weed biomass. Early cover crop sowing five or three weeks before winter wheat harvest increased the weed control efficacy in one year, significantly. Due to contrary results over the two experimental years, we suggest that the cover crop biomass and consequently the weed suppressive ability depends on sufficient soil water for rapid cover crop germination and growth. The use of cover crop mulch in sugar beet crops provided a weed suppression of up to 83%. Especially mulch derived from cover crop mixtures reduced the weed density (56%) more effectively compared to mono cultivated cover crops (31%). The inclusion of cover crops, mulches and living mulches can lead to significant herbicide reductions in the main crop. However supplementary mechanical or chemical weed control strategies are still necessary, especially in crops with a low competitive ability like sugar beets. Nevertheless, novel mechanical weed control approaches and adequate herbicide application techniques, as band-spraying, can reduce the herbicide input in the long-term. Germination tests with aqueous cover crop extracts were conducted on weed seeds to evaluate differences in the inhibition of germination and root growth. Furthermore, different sensitivities of the weeds against the different cover crop extracts were revealed. Some cover crops as S. alba, F. esculentum, H. annuus, T. subterraneum and L. usitatissimum showed the most effective weed suppression. Moreover, the weed M. chamomilla showed the highest susceptibility against biochemical stresses in the germination tests. A strong positive correlation between the weed suppressive effects by the extracts and the field weed suppression was found. This indicated that biochemical effects play also an important role on the overall weed suppression in the field. To estimate the proportions of competitive and biochemical effects on the overall weed suppression by cover crops, greenhouse experiments with active carbon supplemented soil were conducted. These experiments revealed that biochemical effects, by the presence of active carbon in the soil, shifted the balance of competition between cover crops and weeds. In the course of the experiments, we also found species-specific effects on the donor as well as on the receiver side. The results of this thesis demonstrate the diverse use of cover crops, their mulches and living mulches in agricultural systems. This work aims on the optimization of biological weed control strategies and indicates approaches for future research. It is for example not yet clear how cover crops suppress specific weeds and if it is possible to design combinations of specific cover crops for the suppression of individual weed communities. Additionally, these results help to reduce long-term herbicide inputs in agricultural systems.
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.
Integrated weed control in sugar beet (Beta vulgaris), using precision farming technologies and cover cropping
(2017) Kunz, Christoph; Gerhards, Roland
Weed control is one of the major challenges in sugar beet (Beta vulgaris) production worldwide. Due to the high flexibility and low costs, herbicide applications are the common agricultural practice for successful weed control. Yet, due to European and national restrictions, farmers are forced to substitute their herbicide input in order to reduce the chemical influence on the environment. Beside chemical weed control systems, integrated weed management (IWM), can be an alternative, to reduce the chemical preponderance. The five essential parts in composing a successful IWM system are: i) cover crops (CC) and ii) resulting mulch residues which can decrease the weed infestation prior to the actual crop establishment, iii) living mulches which can suppress weeds during the crop growth period and iv) precision mechanical weed control which can provide herbicide reductions. Last but not least v) herbicide applications should be optimized with sensor technologies to identify and reduce stress on crops. In the current study, all the named aspects of IWM were examined in sugar beets. In order to accomplish that, the following research objectives were investigated and answered in the course of the papers composing this thesis: • Evaluation of the suitability of CC and CC mixtures for weed suppression prior to sugar beet sowing • Assessment of differences in sugar beet emergence, weed control and biomass under different CC mulches • Application of living mulches and measurement of their weed control efficacy during the sugar beet growth period • Evaluation of mechanical weed control along with chemical band spraying compared to an overall herbicide application • Determination of the weed control efficacy of mechanical weeding by using visual sensors and GNSS-RTK • Investigation of the feasibility of intra-row mechanical weed control, its prerequisites and limitations • Detection of responses to herbicides by using chlorophyll fluorescence imaging technology 1st paper: Field and laboratory experiments were conducted to investigate the competitive and biochemical weed suppressive ability of CC. Applied aqueous CC extracts in germination tests inhibited weed growth and potential allelochemicals were identified. In the field all CC either in mixture- or mono-cultivation were able to suppress weeds compared to an untreated control by 66%. In the 2nd and 3rd paper sugar beet plant emergence was investigated in greenhouse and field experiments, in order to evaluate the influence of various CC mulches on weed suppression. Different CC mulches reduced weed germination successfully. During one dry growing season sugar beet emergence was enhanced by increased soil moisture due to the existence of a CC mulch layer compared to uncovered soil. Our findings suggest that CC mulch layers can substantially effect crop and weed development within the field. To assess the weed suppressive ability of living mulches in sugar beets, field studies were carried out at four sites in southern Germany, presented in the 4th paper. Results show that living mulches can reduce the total amount of different weed species in the inter-row area up to 71%. The white sugar yield was increased in average by 42% with the existence of living mulch as compared to the untreated control. In the 5th, 6th and 7th paper sensor technologies were used for mechanical weed control combined with chemical band application to reduce the herbicide input, with similar weed control results to the overall chemical application. Sensor based, mechanical precision steering technologies, reduced weeds more effectively than when compared to manual operator guidance. This is due to accurate fast driving speeds close to the crop area. Intra row elements (finger weeder, rotary harrow, torsion weeder, heap element) for mechanical weed control showed effective weed suppression. Nevertheless, suitable soil and weather conditions for mechanical weed control were not always given, which can result in an efficacy loss. Finally, in the 8th paper, a portable sensor, based on chlorophyll fluorescence imaging, was used in greenhouse experiments to investigate the response of plants after herbicide application. Various active ingredients have shown different damage concerning the photosystem II. The use of this sensor can quantify phytotoxic effects due to herbicides and can help to find the most suitable herbicide application date, active ingredients or herbicide mixture. The overall result of this dissertation reveals the great potential of CC, living mulches, precision mechanical methods and sensor technologies as part of an IWM system in sugar beet production.
Weed suppression with cover crops and undersown crops in modern cropping systems
(2014) Brust, Jochen; Gerhards, Roland
The agronomic situation in Germany is characterized by a reduction of crop diversity within crop rotations, which is mainly a consequence of present economic conditions. This results in rare change between fall and spring seeded crops, combined with increasing weed populations. The integration of cover crops and undersown crops into such cropping systems could be a step to reduce the amount of herbicides during crop cultivation but also within a fallow period. The aim of this study was to determine the influence of cover crop and undersown crop cultivation on arable farming systems from the perspective of weed science. Furthermore it should be clarified in which way it is possible to integrate cover crops and undersown crops in intensive cropping systems. Within the cover crop topic this was done by the search for new cover crop species which are suitable for cultivation in Central Europe to expand the range of available cover crop species for lots of cropping situations and site conditions. Additionally the weed suppression ability of different cover crop species in fall and spring was analyzed to determine if it is possible to avoid a mechanical or chemical weed control prior seeding the next cash crop. Within the undersown crop topic the influence of different management practices on growth of undersown crop as well as growth and yield formation of the main crop was investigated. Furthermore, it was researched if it is possible to achieve a suppression of weeds by undersown crops. The conducted experiments relating the cover crop topic showed that from the new cover crop species especially tartary buckwheat, forage radish and lopsided oat are well suited for cultivation. The shoot and root growth of weeds could be effectively reduced by the successful establishment of a cover crop stand in fall. In plots of competitive cover crops like yellow mustard, oilseed radish, tartary buckwheat and lopsided oat, no further growth of weeds and volunteer cereals occurs after the first measurement in fall four weeks after cover crop planting. The weed-suppressing effect of cover crop cultivation was measurable not only in fall during growth, but also in spring after freezing of cover crops. Especially in plots of late freezing cover crop species like oilseed radish and phacelia only a very reduced plant density or even no living weeds and volunteer grains were observed. The conducted experiments relating the undersown crop topic demonstrate that it is possible to integrate undersown crops in high yielding cereal cropping systems without decreasing growth and yield formation of the main crop. During the four conducted field experiments, a reduction in grain yield was only observed when perennial ryegrass was seeded at the three leaves stage of spring wheat and grew under sufficient nitrogen conditions. The study shows that undersown crops are able to reduce weed density during main crop growth. However, the habitus of weeds was an important factor influencing the weed suppression ability of undersown crops. Undersown crops were able to reduce the density of small growing weed species such as Veronica persica while density of high-growing weeds like Chenopodium album were not affected. The experiments in this study offer that is possible to successfully integrate cover crops and undersown crops into modern agricultural systems without reducing their productivity. Furthermore it was demonstrated that due to the cultivation of cover crops and undersown crops it is possible to control the growth of weeds not only during but also between cash crop vegetation. By these methods, under certain conditions a reduction of the required amount of herbicides is possible, which can be a contribution to a more sustainable food production.