2018 Volume 89 Issue 1 Pages 19-25
We monitored soil erosion in two sloping fields that were contaminated with 137Cs to test the effect of cover crops on 137Cs runoff control as a countermeasure for pollutant diffusion caused by rain erosion. In the first field in the Tohoku Agricultural Research Center (slope angle: 4 deg., Low-humic Allophanic Andosols), we established three test plots: the first was sown with Festulolium (×Festulolium Aschers. et Graebn.), the second with soybean (Glycine max) cultivation, and the third was a plowed plot. Then, we monitored soil erosion from June 2013 for 17 months. In the second field (slope angle: 6–7 deg., Allophanic Andosols), in the Yamakiya district of Kawamata Town, decontamination work (removing the top 5 cm of soil and dressing with decomposed granite soil) had been conducted. Here, we established two kinds of cover crop plots and a plowed plot, and it was then monitored from October 2015 for 13 months. In the first cover crop plot, perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), and white clover (Trifolium repens L.) were sown (Pe+Kb+Wc plot) as a combination to cover the ground quickly and persistently with minimal management effort. In the second plot, hairy vetch (Vicia villosa Roth.) was sown as a green manure (Vetch plot). In both fields, cover crops reduced sediment and 137Cs runoff by one order of magnitude than that in the plowed plots and soybean plot. Compared with the Pe+Kb+Wc plot, the Vetch plot had a lower coverage for several months after sowing in September, and consequently, had an 8 times higher 137Cs runoff in December. Thereafter, the differences in coverage and runoff between the plots decreased. Thus, we demonstrated a large-scale runoff control regardless of the grass species that was cultivated.
