Compaction trial at McMaster Chris Guppy- UNE Grain and Graze by lindash


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									    Compaction trial at McMaster
    Chris Guppy- UNE
    Grain and Graze activities at McMaster Research Station, Warialda fall into
    several of the Themes identified as priorities for research and extension
    through the Border Rivers-Gwydir catchment. These activities are found
    all over the research station on soil and land use types that are typical of
    the region. One of these activities is designed to investigate the question
    of whether or not cattle grazing on black cracking clays have an adverse
    effect on subsequent crops. Two trials are proposed to investigate this
    question – the first of which is outlined below. The site of the compaction
    trial at McMaster Research Station is indicated below, as are the other
    Grain and Graze activities (Figure 1).

                        Land use types at McMaster Research Station, 2006.

Legume –
grass mixed
pasture trial                                                                   Compaction by
                                                                                livestock on
                                                                                cropping country

                                                                                GPS tracking of
                                                                                livestock foraging
Temperate                                                                       behaviour
legumes and
variety trials

     Figure 1. Grain and Graze trials and activities at McMaster Research Station, Warialda.
First experiment
A split plot trial will be undertaken, essentially as a demonstration
experiment on a uniform section of land equating to approximately 1.5
ha. The Gray Vertosol is currently under grazing triticale, and the uniform
site was selected following an EM survey (Figure 2).

                                                             Compaction site July 2006 (mS/m)
                                                                 37 - 58
                                                                 59 - 70
                                                                 71 - 81
                                                                 82 - 91
                                                                 92 - 101
                                                                 102 - 112
                                                                 113 - 124
                                                                 125 - 137
                                                                 138 - 149
                                                                 150 - 170


                                                                              W                 E

     0         100         200        300 Meters                                         S

   Figure 2. EM survey of selected paddock with potential trial site indicated in white

The aim is to measure a number of related parameters designed to assess
the impact of cattle on soil physical properties including saturated
hydraulic conductivity, penetrometer resistance and aggregate size
distribution using dry sieving. Following the trial a field day is planned to
demonstrate the effects of cattle on soil physical properties where
preliminary results can be presented, as well as a white paint pit study of
pore size distribution on the variably compacted sites.

On Monday 4th September a group of academics and students will peg out
the trial sites using GPS and line up a sampling transect across each of
the paddocks. The identified trial site will be electrically fenced during the
morning. At least 6 sites in each paddock will have hydraulic conductivity
assessed using a disc permeameter. Following the disc permeameter
measurements (and depending on how far the moisture has managed to
penetrate) a field penetrometer will be used to assess soil strength.
Visual assessment at each of the GPS identified sites on the transect will
determine soil horizonation and subsequently identifiable layers (through
aggregation) will be sampled uniformly and dry sieved to determine the
size distribution. A separate, (fenced if Milton is going to graze the rest of
the triticale around it?), series of control sites (at least 6) will be sampled
external to the two paddocks in the same manner. Soil moisture content
from 0-20 cm will also be determined both in the sampled sites and in dry
adjacent soil.
The fenced areas will then be grazed with different numbers of cattle (12
in one 0.75 ha paddock and 3 in the other) for 21 days. If the GPS
livestock tags are ready in time they will be used to assess grazing
pattern and allow a ‘density’ measure of cattle trampling, particularly
around the watering point.

Following grazing, on approximately the 27th September, the same GPS
identified sites will be resampled using the same parameters to determine
the impact of cattle grazing on soil physical properties in a Gray Vertosol.
The white paint method will also be used to examine pore size distribution
following grazing, digital photography being used to assess changes in
porosity. Should any soil physical effects be observed, the same sites will
again be sampled approximately 2 months after harvest to determine if
there is significant recovery following wetting/drying cycles.

In June 2007, a winter cereal (barley) will be sown over the top of the
trial site. Prior to sowing an EM survey will be conducted to determine if
profile moisture storage was affected by grazing, and subsequently
whether this moisture storage difference resulted in reduced yields. A
control on ungrazed soil, to remove the effects of differential stubble input
(and hence moisture storage efficiency) should involve slashing and
carting the stubble from an ungrazed section of the paddock as a control
comparison on yield. Alternately, an average of the remaining stubble
following harvest of the triticale can be used as the ‘baseline’ to which
stubble levels should be lowered. The growth RATE of the subsequently
sown barley will be monitored 4-5 times during the season, prior to
complete canopy closure, using CropCircles (with destructive harvests of
small areas for calibration).        Any reduction in crop vigour due to
compaction/profile moisture storage can then be recorded. The null
hypothesis in the first trial is that self-mulching Gray Vertosols will remain
unaffected by grazing, and have no impact on the following cereal crop.

Second trial
Presuning there is not heavy rain during the 21 days that the cattle are
grazing in their separated paddocks, it is proposed that a second trial be
undertaken to examine the effects of different pre-existing soil moisture
content on the effect of cattle grazing on soil physical properties. This
study would commence in January/February 2007 and involve the use of
a rainfall simulator to apply different amounts of rainfall to the Gray
Vertosol prior to the introduction of cattle. Systematic, repeated EM
survey of the trial site, coupled with gravimetric measurement of soil
moisture content in the upper 20cm of the soil profile will be used to
monitor the impact of cattle on infiltration, aggregate stability and soil

Cattle will be allowed to wander (hay bales etc) overall the sites for 3
days to compact the soil, and will be GPS tagged to ensure reasonably
even trampling distribution. Before and after compaction, soil physical
parameters as indicated in the First trial, will be measured. An EM survey
will be conducted to look at profile moisture levels, and after 7 days and
28 days the rainfall simulator will apply a uniform amount of water across
all sites. Runoff, erosion and profile moisture retention can then be
assessed, through both physical measurement and EM survey. The
details of this second trial can be determined closer to the middle of
summer! It may be possibly, given timely storm events to assess
following storms?

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