These results are closely reflecting the effect of residue removal,
tillage and fertilization practices on corn yields (Coulter and Nafziger,
2008; unpublished data of the authors since 2007). In poorly-drained,
productive soils of Illinois, with annual corn yield averages of 10 Mg/ha
or more, removing residue increases yield regardless of tillage, but
more under no-till than when tilled. The positive quadratic response to
N fertilizer rate is also accentuated with tillage, though the magnitude
of this response varies with weather conditions. Thus we see that residue
and its removal have effects that extendwell beyond those of short-term
changes in soil C, N, and other nutrient levels, and include such things as
effects on soil temperatures and soil water retention that are unrelated to
small changes in C and nutrient stocks.5. Conclusions
Under the temperate weather, high yielding, and high fertility soil
conditions of Illinois, residue removal, with or without tillage, appears
to represent little threat to soil productivity, at least over a period of
five years, and as long as removed nutrients are replenished. By increasing
grain and biomass yield, higher N rates increased estimated nutrient
uptake and stover content, thereby increasing the amount nutrients removed
when residue was removed. Removing all of the residues at the
highest yield levels removed only 10 kg of P ha−1 over 5 years, and so
the drop in soil P with full residue removal and as N rate increased
was due to factors other than removal of P alongwith residue. Actual removal
of N and K was likely overestimated because of weathering after
harvest in the current work, but maximum removal levels that
exceeded 200 kg ha−1 over five years may be enough to influence soil
K levels. Yet a longer term evaluation of these practices is required to
generate responsible recommendations regarding residue removal
rates integratedwith tillage and fertilization options if corn crop residue
is to provide a major feedstock to support a sustainable bioenergy
industry.
Acknowledgments
This research was supported in part by the North Central Regional
Sun Grant Center at South Dakota State University through a grant provided
by the U.S. Department of Energy Office of Biomass Programs
#802 DOE Sub SDSU 3TP146 and through a grant fromthe Illinois Fertilizer
Research & Education Council, Project #335.We acknowledge with
gratitude the work of Lyle Paul, Eric Adee, Martin Johnson, Mike Vose,
Mike Kleiss, Krishna Woli, and Joe Little in plot care and sample collection
and analyses.