Influence of soil structure on contaminant leaching from injected slurry

Authors: AMIN, MOSTOFA - Pennsylvania State University; OSTERBALLE PEDERSEN, CHRISTINA - Bangladesh Agricultural University; FORSLUND, ANITA - Danish Technical University; Veith, Tameria - Tamie; LAEGDSMAND, METTE - University Of Copenhagen

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2016
Publication Date: 10/8/2016
Citation: Amin, M., Osterballe Pedersen, C., Forslund, A., Veith, T.L., Laegdsmand, M. 2016. Influence of soil structure on contaminant leaching from injected slurry. Journal of Environmental Management. 184(2):289-296. doi:10.1016/j.jenvman.2016.10.002.

Interpretive Summary: To fully understand the water quality impacts of applying liquid manure on crops, we must better understand the differences in liquid manure movement through soil with macropore structures, as found in the field, and through soil without macropore structures, as typically found in laboratory soil columns. We collected nine soil columns from a crop field, repacked three of the columns to match typical laboratory studies, and studied the liquid manure that either drained through or remained in the soil after four simulated rainfall events. Because rain water drained more slowly through the repacked soil columns and allowed more time for the water and liquid manure to interact, less nitrogen and more microorganisms drained through the repacked columns than the undisturbed field columns. This study demonstrates the importance of considering soil structure effects when scaling study results from standard soil column studies up to the field-level in order to estimate the impacts of management practices such as reduced tillage and manure injection on controlling nutrient and microorganism losses.

Technical Abstract: Animal manure application to agricultural land provides beneficial organic matter and nutrients but can spread harmful contaminants to the environment. Contamination of fresh produce, surface water and shallow groundwater with the manure-borne pollutants can be a critical concern. Leaching and persistence of nitrogen, microorganisms (bacteriophage, E. coli, and Enterococcus) and a group of steroid hormone (estrogens) were investigated after injection of swine slurry into either intact (structured) or disturbed (homogeneous repacked) soil. The slurry was injected into hexaplicate soil columns at a rate of 50 t ha-1 and followed with four irrigation events: 3.5-h period at 10 mm h-1 after 1, 2, 3, and 4 weeks. The disturbed columns delayed the leaching of a conservative tracer and microorganisms in the first irrigation event compared to the intact columns due to the effect of disturbed macropore flow paths. The slurry constituents that ended up in or near the macropore flow paths of the intact soil were presumably washed out relatively quickly in the first event. For the last three events the intact soil leached fewer microorganisms than the disturbed soil due to the bypassing effect of water through the macropore flow path in the intact soil. Estrogen leached from the intact soil in the first event only, but for the disturbed soil it was detected in the leachates of last two events also. In contrast, NO3-N leaching from the intact soil was higher for all events except the first event, probably due to a lower nitrification rate in the disturbed soil. A week after the last irrigation event, the redistribution of all slurry constituents except NO3-N in most of the sections of the soil column was higher for the disturbed soil. Total recovery of E. coli was significantly higher from the disturbed soil and total leaching of mineral nitrogen was significantly lower from the disturbed soil. Results suggest that tillage and other structural soil disturbances prior to manure injection can impact the fate of different slurry constituents in conflicting and unexpected ways.