- P. Neave, V. Thomas, Department of Zoology, University of Guelph, Guelph,
Evaluation Summary (Tech. Transfer Report Summaries)
Associated SWEEP/LSP Research
View / Download Report [596 KB pdf]
Completed: October, 1991
soil microbiology, soil biology, soil quality, no-till, pasture soils,
spring plowing, earthworms, nematodes, cryptozoic invertebrates, mites,
springtails, bulk density, infiltration, soil temperature
The purpose of this study is to use populations of soil organisms to
contrast ecosystem stability in an undisturbed pasture with a zerotill winter
wheat field. Soil organisms that were considered include soil microbial
biomass, nematodes, earthworms, soil dwelling arthropods, cryptozoic invertebrates,
and emergent arthropods. The pasture represents a more natural ecosystem
as it is undisturbed agriculturally, and the zerotill field represents an
actively managed agroecosystem.
Stability was measured by perturbing the populations of soil microflora
and fauna by plowing and disking the soil, and measuring their time to return
to, deflection from, and rate of return to, the ground state. Return time
was faster and deflection from ground state was less in the zerotill agroecosystem
than in the pasture system. These results suggest that agroecosystems are
not unstable, as communities within the agroecosystem can recover from perturbation.
Diversity, as measured by richness and evenness, was similar in pasture
and zerotill soil for those populations for which it was determined.
Litter decomposition rate (LDR) was measured using litterbags. LDR was
faster in the zerotill plowed system compared to pasture plowed, possibly
because of the more rapid return of macro-invertebrates in the plowed soil.
Differences in soil microbial biomass do not appear to account for differences
Saturated hydraulic conductivity (SHC) and dry bulk density (DBD) were
used to measure pore continuity. In the zerotill system, SHC and DBD were
significantly higher in the unplowed soil indicating that pore continuity
is much higher in unplowed soil. In the pasture system, plowed soil had
a higher SHC and a similar DBD to that of unplowed soil indicating that
pore continuity is higher in plowed soil, possibly because of the destruction
of roots previously plugging the pores of unplowed soil.
Water infiltration rate was found to be correlated with the number of
earthworms in pasture and zerotill unplowed and plowed soils. This illustrates
the importance of bioporosity in these soils.
The recommendation to plow zerotill soils every 4-5 years is put into
question by this study. The soil quality indicators of earthworm number,
water infiltration rate and pore continuity indicate that plowing zerotill
soil may not be beneficial. Chisel plowing or ridge tillage might be acceptable
Number of mites and richness and abundance of soil dwelling arthropods
were modelled against various environmental parameters. Cropping system
(pasture or zerotill), depth, and organic matter content appear to strongly
influence the distribution of soil dwelling arthropods. Tillage (yes or
no), water content and wet bulk density were not as important determinants.
Number of mites did vary with depth over the season, numbers increasing
with depth in the plowed soil, and decreasing with depth in the unplowed
soil. Mites returned to the upper levels of plowed soil when temperatures
and vegetational growth returned to similar levels to that of the unplowed
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
A one year study using soil organisms to contrast the agro-ecosystem
stability in an undisturbed pasture with a zero-till winter wheat field
in plowed and unplowed plots. Four treatments were studied: a pasture field
and a zerotill field; each of these were split in half, one side was moldboard
plowed and the other was left unplowed. Numerous parameters were evaluated
and results are as follows:
Abundance of nematodes - The number of nematodes was initially higher
in zero-till than in pasture but towards the end of the growing season
nematode numbers were higher in pasture soil. Number of nematodes correlated
with saturated hydraulic conductivity in pasture soil, therefore in this
soil, pore size might be limiting the activity of nematodes.
Earthworms - The number of earthworms in all sample plots were at a
maximum at the end of the season (November). At the end of the season
the number of earthworms in unplowed pasture soil was more than double
that in unplowed zero-till soil. Pasture soil may take several years for
populations to return. Earthworm populations do not appear to recover
fully from plowing even after six months.
Cryptozoic invertebrates - The abundance of invertebrates was generally
low in the spring, high in the summer and low again in late fall. There
was no significant difference among plots. Slugs were similar in numbers
in pasture and zero-till plots. The highest numbers were in plowed pasture
and unplowed zero-till soils at the end of the sampling period. Similar
trends were found for sowbugs except the number of sowbugs were higher
in unplowed pasture than in plowed soil in mid-summer.
Mites and springtails - The occurrence of mites and springtails were
similar in all plots. The average number of animals in unplowed pasture
and zero-till was higher in the surface soil (0-5 cm). In plowed pasture
and zero-till the numbers were found at greater depths (5-15 cm). Tillage
alone doesn't influence distribution of mites. Changes in the soil after
tillage has a greater influence.
Soil Biomass - Soil biomass was almost always higher in pasture soil
regardless of whether it was plowed or unplowed. Soil biomass C:P ratios
were generally higher in pasture soil than in zero-till.
Litter decomposition rate (LDR) - The LDR was higher in zero-till plowed
soil than in pasture plowed soil 39 and 69 days after plowing.
Dry Bulk Density (DBD) - DBD was similar in unplowed and plowed pasture
soils and was significantly higher in zero-till unplowed versus plowed
Infiltration rate - Infiltration rate was higher in unplowed pasture
and zero-till soils than in plowed soils. The average infiltration rate
increased with increasing earthworm numbers and earthworm mass. The higher
infiltration rate in unplowed soils at this site could be due to biopores
transmitting more water than macropores.
Soil temperature in the plowed zero-till and plowed pasture soils had
higher temperatures than unplowed soils. This difference disappeared by
Water content - There was no significant difference in water content
amongst the plots.
Stability - Return times of population parameters were faster in zero-till
soil. The zero-till community was more stable (by definition) than the
Diversity as measured by richness (number of species per catch) and
evenness were the same in zero-till and pasture soils.
Some conclusions from the report are:
Plowing reduces earthworm populations (even after six months) and reduces
the water infiltration rate.
The study shows a long time is required for zero-till soil to "peak"
The zero-till community is more stable than the pasture community.
This is a good report (although very technical) with some interesting
trends showing up. From this report it would seem that we should not be
recommending to plow zero-till soil 4-5 years into the system to mix the
soil. This would harm earthworm numbers and infiltration rates. It is important
to note that our soils tend to be very stable ecosystems and return times
for organisms are relatively quick after cultivation (except for earthworms).
SWEEP Report #47 - Effect of Woodlot Borders
and Crop Residue on the Distribution of Invertebrates in Agroecosystems
SWEEP Report #37 - Effects of Tillage on the
Quality and Quantity of Surface and Subsurface Drainage Water: Uplands
LSP 7016 - Response of the Soil Microflora
and Fauna to Spring Plowing of Zerotill and Pasture Soils
Future Research: ( ) indicates reviewers suggestion for
priority, A - high, C - low.
(A) Future research into soil life should differentiate, where possible,
amongst soil organisms which are beneficial to agriculture and those that
are not. It would be interesting to see differences amongst zero-till, minimum
till and moldboard plow systems examined.
Thursday, May 19, 2011 02:44:49 PM