Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2010
Publication Date: 8/1/2010
Citation: Udawatta, R., Kremer, R.J., Anderson, S.H. 2010. Influence of Herbicide on Microbial Resilience in Soils Under Contrasting Management. In: Gilkes, R.J., Prakongkep, N., editors. Proceedings of the 19th World Congress of Soil Science, August 1-6, 2010, Brisbane, Australia. p. 72-75. Interpretive Summary: The ability of soil to provide critical functions including the support of plant productivity by supplying available nutrients and other necessary growth conditions often depends on resistance to disturbance of soil properties and resilience of soil processes following degradative activities or perturbations. Concern exists regarding seasonal applications of herbicides to crop production fields and their potential for disrupting soil processes and subsequent environmental degradation. To address these concerns, we examined the effects a widely used herbicide, glyphosate (commercially available as Roundup™), on the resilience of microbial activity in soils under contrasting management practices. Although glyphosate is primarily applied to foliage, considerable amounts indirectly reaches the soil surface and subsequently enters upper layer of soil. Glyphosate solutions were applied at various concentrations to soil from fields under crop cultivation and from permanent grassland sites. Soil biological activity was assessed by measuring enzyme activity, which indicates the functioning of important processes relative to decomposition of organic substances and making essential nutrients available for plant growth. Glyphosate at all concentrations suppressed microbial activity in all soils, however, activity returned to levels in non-glyphosate treated soil within five days for a native prairie whereas soil from the cropping system required 10 days for restoration of microbial activity. Results suggest that prairie soils and the grassland soils under minimal disturbance were more resilient in restoring microbial activity compared with the cropped soils that experience annual disturbance due to planting, chemical application, and harvest activities. The results are important for soil scientists, extension personnel, landowners, and farmers because they provide information that may be useful for selecting crop management systems and chemical programs that will have minimal effects on soil biology and ultimately on overall soil quality.
Technical Abstract: The objective of this study was to examine soil microbial resilience in response to herbicide application on soils from prairie and row crop management. The management treatments were: native prairie (TP), restored prairie (PF), conservation reserve program (CRP), and corn-soybean rotation (CS) management. Surface soil (10 cm) was collected from two locations within each treatment with four subsamples per location in June 2008. Soil enzymes assessed included: fluorescein diacetate hydrolase (FDA) and dehydrogenase. Eleven glyphosate concentrations (0 to 2000 ppm) were applied using the commercial formulation (Roundup Original Max(TM)); soil dehydrogenase and FDA hydrolase activities were assayed periodically over 50 days. Soil enzyme activities were lower on days one and ten irrespective of enzyme type or management. The highest enzyme activities were observed on day 5 and the activity declined thereafter. However, some soil treatments exhibited increased activity on days 30 and 50. Herbicide concentration had a smaller effect on FDA hydrolase activity while the effect of concentration was highly variable for dehydrogenase activity. Results of the study show that soils from native prairie have greater enzyme resilience while cropped soils have the lowest. Establishment of prairie vegetation may help maintain active soil processes and could help maintain or improve soil quality.