Soil management legacy alters weed-crop competition through biotic and abiotic pathways

Authors: GAN, HUIJIE - Cornell University; Emmett, Bryan; DRINKWATER, LAURIE - Cornell University

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2021
Publication Date: 2/22/2021
Citation: Gan, H., Emmett, B.D., Drinkwater, L.E. 2021. Soil management legacy alters weed-crop competition through biotic and abiotic pathways. Plant and Soil. 462:543-560. https://doi.org/10.1007/s11104-021-04891-3.
DOI: https://doi.org/10.1007/s11104-021-04891-3

Interpretive Summary: Weed management is an important challenge in agricultural systems and growers in low input and organic production systems need improved strategies for managing crop/weed competition. We investigated whether soil fertility and soil microbial communities alter competitive interactions between grain sorghum and two common agricultural weeds, Ambrosia artemisiifolia (ragweed), and Amaranthus powellii (pigweed). A greenhouse experiment was conducted using two soils with a history of conventional vs. organic management that has led to large differences in soil fertility and soil microbial communities. We then used cross-inoculations of the microbial communities to separate the effects of the soil biota vs the soil abiotic environment on crop and weed growth. We found that high soil fertility (organic soil) led to increased weed growth at the expense of sorghum. However, inoculation with the high fertility microbial community improved sorghum competitiveness in both soil environments. These results suggest that long-term organic management has the potential to promote beneficial soil microbial communities that increase crop competitiveness against some weeds and that soil fertility should be managed to optimize crop performance and competitiveness. Weed scientists, agronomists and biotechnology companies focused on microbial products can use these results to develop weed management strategies for systems where herbicide use is limited.

Technical Abstract: Aims: Agricultural practices often have persistent effects on soil physicochemical properties and microbial community. Management legacy in soil can further feedback to influence plant performance, but the underlying mechanisms are not fully understood. We investigated management-induced differences in soil fertility and microbial communities for their legacy effect on plant nutrient acquisition and crop/weed competition. Methods: Sorghum bicolor (L.) Moench (sorghum), Ambrosia artemisiifolia (L) (ragweed), and Amaranthus powellii S. Wats. (pigweed) were grown as monocultures and mixtures in the greenhouse in soils with distinct management histories. Soils were sterilized and then inoculated with microbes of the same or different origins. Plant biomass, nutrient uptake, and mycorrhizal colonization were quantified after two months. Results: Soil under long-term organic management exhibited significantly higher organic matter (HOM) than conventionally-managed soil, resulting in a 37% increase in N acquisition in all species. The high N availability preferentially benefit pigweed growth which in turns exerted stronger competition on sorghum. However, microbes from the HOM soil alleviated the negative effects of pigweed competition on sorghum. In addition, HOM microbes stimulated axillary tiller emergence in sorghum. Mycorrhizal colonization was higher in the HOM soil than in the low OM soil (LOM), and was negatively correlated with ragweed N acquisition when ragweed was in competition with sorghum. Conclusion: Management-induced difference in soil biotic and abiotic factors altered plant performance in a specie-specific manner. Long-term organic management has the potential to promote beneficial soil microbiomes that increase crop competitiveness against some weeds.