Effects of organic and conventional cropping systems on plant diversity and plant soil feedbacks
Johnson, Stephen Patrick.
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The reliance on tillage for cover crop termination, weed, and residue management is one of the biggest sustainability challenges facing organic grain farmers. Integrating grazers may be an alternative to tillage for weed management and cover crop termination. We used an on-farm trial to compare tillage-based versus grazed / reduced tillage-based management of organic crops. Our results indicate that using sheep to terminate cover crops andmanage weeds can reduce tillage intensity and provide crop yields weed communities similar to standard, tillage-intensive practices. In addition, growers leasing their land under a grazing lease may be able to increase economic returns. We also implemented a crop rotation study comparing traditional tillage-based organic to reduced-tillage organic with animal-integration, as well as to a no-till conventional system with fertilizer and pesticide inputs. There were no differences in cover crop growth and subsequent winter wheat yielded the same among the three systems. We found little evidence that weed communities differed among the three management systems in the transition to organic period. Generally, shifts in weed communities occurred across all system from one crop to the next, indicating cropping sequence structured weed communities more than divergent tillage and weed management practices Biologically-mediated plant-soil feedbacks (PSFs) are known to alter plant growth, plant-plant interactions, and plant community dynamics in natural systems. Yet, little is known about the magnitude and importance of PSFs in agro-ecosystems. Therefore, we implemented a greenhouse study that investigated the impact of organic and conventional management systems on crop growth and crop-weed interactions as mediated through PSFs. Results indicated that in general, PSFs and plant growth were more positive when soil inocula was collected from organic farms compared to conventional farms, suggesting that cropping systems modify the relative abundance of mutualistic and pathogenic organisms responsible for the observed PSFs. Also, as feedbacks became more positive, crop-weed competition decreased and facilitation increased. Therefore, in annual cropping systems, PSFs can alter plant growth and crop-weed competition.