Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2009
Publication Date: 9/28/2009
Citation: Ramirez, N., Wang, P., Lejeune, J., Shipitalo, M.J., Ward, L., Sreevatsan, S., Dick, W. 2009. Effect of Tillage and Rainfall on Transport of Manure-Applied Cryptosporidium Parvum Oocysts through Soil. Journal of Environmental Quality. 38(6):2394–2401. Interpretive Summary: Animal manures are a valuable resource for crop production, but can contain oocysts of the disease causing organism Cryptosporidium. The factors that affect the movement of oocysts in land-applied manure through soil, however, are poorly understood. In this laboratory study we evaluated the effect of rainfall timing and intensity and storm sequence on oocyst transport through undisturbed blocks of tilled and no-till soil. When we applied liquid dairy manure spiked with Cryptosporidium oocysts to no-till soil some of the manure and oocysts were immediately transmitted through the 30-cm deep blocks, but no manure or oocysts were transmitted when the upper 10 cm of the blocks were tilled. When simulated rainfall was applied to the manure-treated tilled and no-till soil oocysts were detected in the leachate, but the numbers transmitted were much greater for the no-till soil. Delaying the first rain for 48 hours or light rainfall preceding a heavy rainfall greatly reduced oocysts transport for both tillage treatments. Large pores created by roots and earthworm activity contributed to the greater oocyst movement in the no-till soil, but the continuity of these macropores was disrupted in the tilled soil. These results suggest that farmers can reduce the potential for oocyst transport to groundwater or subsurface drains by avoiding manure application when heavy rainfall is expected within 48 hours or by lightly tilling the soil above the drains to disrupt the macropores. These measures will help to preserve the many benefits associated with no-till production practices.
Technical Abstract: Most waterborne outbreaks of cryptosporidiosis have been attributed to agricultural sources due to the high prevalence of Cryptosporidium oocysts in animal wastes and the practice of spreading manure on farmlands. No-till is an effective soil conservation practice, but it often results in soil having higher water infiltration and percolation rates than conventional tilled soil that may facilitate the transfer of pathogens to groundwater and subsurface drainage systems. Therefore, we treated six undisturbed no-till and six tilled surface soil blocks (30 by 30 by 30 cm) with liquid dairy manure containing C. parvum oocysts to test the effect of tillage and rainfall on oocyst transport. Two, 4, 24, or 48 hours after manure application the blocks were subjected to simulated rainfall consisting of heavy (30 mm in 30 min) or light rainfall (5 mm in 30 min). Leachate was collected from the base of the blocks in 35 mL increments using a 64-cell grid lysimeter. After percolation ceased the blocks were sectioned into eight, 3.75-cm-thick horizontal slabs. The leachate and soil samples were subjected to oocyst detection and enumeration. Simulated rainfall applied 2 hours after manure addition increased oocyst transport up to 85-fold through no-till compared to tilled soil blocks while oocyst retention in the soil was up to 21-fold higher in tilled blocks. Oocysts transport was greatly reduced when rainfall occurred 48 hours after manure application. This suggests soil tillage, and rainfall timing and intensity, affect transport of C. parvum oocysts through the soil. To minimize transport of Cryptosporidium in manure applied to no-till fields, manure should be applied at least 48 hours before heavy rainfall is anticipated or methods of disrupting the direct linkage of surface soil to the drains via macropores need to be used.