Effect of Dairy Slurry Application on Soil Compaction and Corn Yield in Southern Wisconsin

As stocking rates on Wisconsin dairy farms continue to increase, one possible nutrient
management solution is to haul slurry to nearby grain farmer’s fields. Although the
nutrient and soil building benefits of manure are well known, many grain farmers are
hesitant to apply manure on their fields due to potential soil compaction. Studies were
initiated to evaluate the effects of tanker-applied slurry on soil compaction and corn (Zea
mays L.) yield. An on-station trial was established to address the issues of compaction
caused by manure tankers, repeated traffic associated with field headlands, and the
possible ameliorating effect of manure itself on corn yield. In addition, 15 replicated onfarm
trials were established to evaluate the impact of single pass manure applications on
soil compaction and yield. These predominately fall applications were conducted when
the host farmer felt that the soil would support tanker traffic. Due to its portability and
instrument sensitivity, compactness was evaluated with a data-logging hand held
Results from the on-station trial indicate that multiple passes did increase compactness
above single-pass traffic and the check. The slurry itself did not attenuate the effect of
traffic on soil compaction, nor on yield. Despite yield reductions estimated from in-track
samples in both years of 6% (one-pass traffic) and 22% (six-pass traffic) in this study, whole
plot corn yields were not reduced due to compaction. The on-farm trials indicated that
manure application technique does affect compaction patterns; with broadcast
application resulting in less area trafficked by the tanker than injection application,
and therefore less area compacted. The narrower gauge truck tires used at some sites led to
significantly higher penetrometer readings compared to the control, but this was not the
case at sites with wider tractor tires. As in the on-station work, although compaction led to
higher penetrometer readings, whole plot corn yields in compacted plots were not
adversely affected compared to the control. These results suggest that, in the first year
after slurry application, on predominantly prairie derived soils; well-timed applications of
dairy slurry do not cause extensive soil compaction nor a reduction in corn yields. This
study did not look at the potential residual effects that may positively (>soil organic
matter) or negatively (residual soil compaction) impact subsequent crops.

Authors: G. Sanford, J. Posner, R. Schuler, J. Baldock

Published in Soil & Tillage Research (2008) 100:42-53