Agriculture Reference
In-Depth Information
greater infiltration rate related to loosening of topsoil by light trampling compared
with lower infiltration rate at higher stocking rates. An ungrazed control had greater
bulk density and lower infiltration rate compared with the light stocking rate. In dairy
systems, where soil pugging may be more intense, Singleton and Addison (1999)
cautioned to manage grazing to minimize long-term compaction of the soil profile.
Mills and Fey (2003) synthesized South African research and found that removal
of vegetative cover by tillage, grazing, or burning reduces SOC and increases soil
crusting. Interactions of SOC with soil mineralogy influences clay dispersion and
crusting, and the relationship must be understood in finding appropriate soil quality
indicators. Francis et al. (2001) showed that, after 6 years under pasture, several soil
quality attributes had improved compared with soil cropped annually. However, the
improvement during 3 years under perennial pasture was of similar magnitude to
the decline under 3 years of cropping. They suggested that similar lengths of pastoral
and arable cropping are needed in crop rotations for the long-term maintenance of
the crop-livestock systems they evaluated.
In the southeastern United States, stocker cattle (young, weaned animals weigh-
ing 70-350 kg head
−1
) managed for 3 years with a near-continuous grazing system
(January to October) on Tift-44 Bermuda grass pasture overseeded with rye (
Secale
cereale
) resulted in greater bulk density (1.63 Mg m
−3
) than under pasture excluded
from cattle grazing (1.50 Mg m
−3
) (Tollner et al. 1990). Another study in the region
showed soil bulk density at a depth of 0-6 cm declined with time from 1.53 to
1.26 Mg m
−3
due to accumulation of surface soil organic matter. Bulk density tended
to be greater at the end of summer grazing than before summer, but was not signifi-
cantly affected by grazing with stocker cattle as compared with ungrazed plots dur-
ing the first 5 years of management (Franzluebbers et al. 2001). These results suggest
that cattle trampling could have both negative and neutral effects on soil compaction,
likely depending on soil water content, vigor of plant growth recovery following
grazing, stocking rate, and/or landscape features.
In the Midwest United States, soil bulk density was not affected by winter grazing
of corn stalks for 1-month periods in the winter (Clark et al. 2004). The estimated
corn residue consumption by cows was only 9%, so grazing time and trampling were
minimal. In the southeastern United States, winter grazing by cattle of a rye cover
crop following soybean (
Glycine max
[L.] Mer.) for 3 years resulted in surface soil
bulk density that was not different from the same cropping system that was not grazed
when managed with conventional disk tillage (1.50 Mg m
−3
). With no-till manage-
ment, the bulk density of grazed plots was greater than that of ungrazed plots (1.60
vs. 1.52 Mg m
−3
) (Tollner et al. 1990). Disk tillage apparently removed any evidence
of compaction. In contrast, grazing of winter and summer cover crops by cow-calf
pairs in Georgia did not significantly alter surface bulk density under either con-
ventional tillage or no till (Franzluebbers and Stuedemann 2008b). SOC, total soil
nitrogen, and mineralizable carbon and nitrogen were unaffected by grazing of cover
crops; however, soil microbial biomass carbon was sometimes enhanced with grazing
(Franzluebbers and Stuedemann 2008a). Deep-profile SOC was unaffected by graz-
ing of cover crops; however, greater SOC was retained following termination of pas-
ture with no till than with conventional tillage (Franzluebbers and Stuedemann 2013).
The surface 5 cm of a soil in Argentina had greater bulk density with winter grazing
