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Browsing by Author "Smith, R. G."

Now showing 1 - 2 of 2
  • A new hypothesis for the functional role of diversity in mediating resource pools and weed-crop competition in agroecosystems
    Smith, R. G.; Mortensen, D. A.; Ryan, M. R. (Oxford, UK: Wiley-Blackwell, 2010)
    We develop a new conceptual model we call the Resource Pool Diversity Hypothesis (RPDH) aimed at explaining how soil resource pool diversity may mediate competition for soil resources between weeds and crops. The primary tenets of the RPDH are that (i) in plant communities, the intensity of inter-specific competition can depend upon the degree to which niche differentiation and resource partitioning occur among species, (ii) agricultural systems are unique in that management practices, such as crop rotation, source of fertility and weed management, result in inputs to the soil and (iii) these inputs directly or indirectly become soil resource pools from which crops and weeds may partition resources. The RPDH leads to the novel prediction that along a gradient of increasing cropping system diversity, yield loss due to weed-crop competition (i.e. the impact on yield per unit weed density) for soil resources should decrease. Similarly, the degree to which crops and weeds overlap in soil resource niche breadth (which is determined by species-specific functional traits for resource acquisition), will determine the extent to which weed-crop competition weakens as resource pool diversity increases. While there have been no direct tests of the RPDH, we highlight evidence from the agricultural literature that provides strong support for components of the hypothesis. Validation of the RPDH would have important implications across a broad range of cropping systems for the development of management strategies that aim to reduce yield loss impact per unit weed plant density and the fundamental principles of integrated weed management, such as the concepts of weed thresholds and critical periods. (CabAbstracts)
  • Weed-crop competition relationships differ between organic and conventional cropping systems
    Ryan, M. R.; Smith, R. G.; Mortensen, D. A.; Teasdale, J. R.; Curran, W. S.; Seidel, R.; Shumway, D. L. (Oxford, UK: European Weed Research Society, 2009)
    Experiments comparing conventional and organic systems often report similar yields despite substantially higher weed abundance in the organic systems. A potential explanation for this observation is that weed-crop competition relationships differ between the two types of systems. We analysed weed and crop yield data from the Rodale Institute Farming Systems Trial (FST), which provides a unique 27-year dataset of a conventional (CNV) and two organic [manure (MNR) and legume (LEG)] soyabean (Glycine max (L.) Merr.) and maize (Zea mays L.) cropping systems. Average soyabean yields were similar between the MNR and CNV systems and only slightly reduced in the LEG system, whereas average maize yields did not differ among systems despite the two organic systems having more than four and six times greater weed biomass in soyabean and maize respectively. Plot-level weed biomass-crop yield relationships indicated that weed-crop competition differed between the two organic and CNV systems in maize, and was strongest in the CNV system, intermediate in the LEG system and weakest in the MNR system. These results suggest that organic cropping systems may be able to tolerate a greater abundance of weeds compared to conventional systems and that fertility management within organic systems may influence weed-crop competition. (CabAbstracts)