Reduced Waterlogging Of Pastures Trial
Darren and Michelle Evans, Derrinallum.
Graeme Ward, PIRVic, Warrnambool
Tim Johnston, PIRVic Geelong
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Milestone 5 - Annual Report - Results for the 2006 Season
February 2007
Disclaimer
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Graph: D&M Evans Monthly Rainfall (So you wonder why we didn't get any runoff this year!?)
Contents
Results and Discussion
Executive summary
During 2006, a field trial designed to quantify the effect of two different surface drainage strategies of pasture (hump & hollow and raised beds) on farm productivity, profitability and sustainability was conducted on a commercial farm near Derrinallum as part of the Corangamite/Glenelg-Hopkins “Grain & Graze” program. Unfortunately, despite above average rainfall for January, February and April, severe drought conditions prevailed with total rainfall for the year being in decile 1. As a result of these rainfall deficiencies for winter and spring, no surface runoff or waterlogging of pastures occurred during 2006. Therefore, the effect of the hump & hollow and raised bed drainage treatments compared to the undrained control on surface runoff, pugging damage and trafficability could not be determined.
However, the effect of the two drainage treatments in a dry year on the pasture and animal productivity was determined. Significantly, the raised bed drainage treatment had lower pasture productivity growing only 4.81 t DM/ha for the year compared with 7.05 t DM/ha for the hump & hollow and 7.61 t DM/ha for the control. A large part of this lower DM yield on the raised beds is likely to be a result of a poor establishment of the autumn oversown Italian ryegrass on the raised beds. Despite having a satisfactory initial establishment, the ryegrass seedlings in this treatment suffered from serious moisture stress leading to a high mortality and an open pasture with more bare space. This was then reflected in lower animal production for the raised bed treatment. Lambs from all three treatments had similar liveweights at weaning in early November, but the raised beds was only able to be stocked at 4.3 ewes/ha over the spring period compared to 5.2 and 5.4 ewes/ha for the control and hump & hollow treatments respectively.
Marked differences in soil physical health were found between the topsoils of the different treatments. Most notable was the aeration porosity of the soils at field capacity (10 kPa). The control treatment had a porosity of only 6.5% at 10 kPa, indicating that this soil had lost most of its macro, or large pores due to treading. This value is well below the well recognized critical level of 10%, below which plant growth can be restricted through poor root aeration. In contrast the raised beds and hump & hollow had values of 15.7% and 11.5% respectively. The change in pore size distribution in the soils from these different treatments was also found to have a marked effect on the water holding capacity of these soils. The plant available water (PAW) of the top 10 cm of these soils was found to 28.5 mm for the control, but only 19.8 mm and 17.8 mm for the hump & hollow and raised beds respectively. This reduced water holding capacity may have contributed to the markedly poorer productivity of the pastures on the raised beds under the drought conditions of 2006.
Darren and Michelle Evans, Derrinallum.
"Grain & Graze"
Reduced Waterlogging of pastures trial
Project Aim
The aim of this project as stated in the Grain & Graze project brief is to;
Quantify the effect of surface drainage on farm productivity, profitability and sustainability (both on and off farm).
The trial is designed specifically to monitor the effect of surface drainage on:
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Pasture productivity and nutritive value.
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Animal production.
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Waterlogging severity and duration.
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Trafficability and soil physical condition.
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Monitoring of waterflows off the site.
Note that until additional funding is obtained, the project does not include monitoring of nutrient losses in runoff water.
Purpose of Milestone 4.
As part of the contract between Southern Farming Systems Limited and the Department of Primary Industries, a progress report, Milestone 4 – “Annual report on results from monitoring for 2006, including extension activities” is required. The purpose is to formally report on and present the relevant findings from the first year’s (2006) operation of the trial. Milestone 4 was originally specified to be delivered on 01 February 2007. However, due to the heavy commitment of project staff in fire suppression activities during December 2006 and January 2007, the delivery date was renegotiated to 01 April 2007.
Trials site and design
The trial is being conducted on a “Grain & Graze” surface drainage demonstration paddock established on the property of Darren and Michelle Evans, Kurweeton Road Derrinallum. The 23 ha paddock had raised beds (2 m wide) and hump and hollow(25 m wide) drainage installed on approximately one third each of the paddock during the autumn of 2005, with the remaining one third of the paddock being left as an undrained control area. The paddock was sown to hybrid perennial ryegrass (Lolium perenne L. cv. Horizon) and white clover (Trifolium repens L. cv. winter white) in June 2005, with some areas requiring resowing in August 2005. In October 2005, the paddock was fenced along the boundaries between treatment areas to form six small paddocks: two in each drainage treatment – larger paddocks to the west of the north-south drain dissecting the paddock, and smaller paddocks to the east of this drain (Figure 1). The larger paddocks to the west of the drain, hereafter called “plots”, are used as the experimental areas for the trial, whilst the smaller paddocks to the east be used as part of the grazing rotation, but no experimental observations are collected from them.
During January-February 2006 a road grader was used to form hydraulically isolated treatment catchments in each of the western side of the raised bed, control and hump & hollow treatment paddocks (Figure 1). Each of these catchments are 2.5 ha in size and have flumes and automated water measurement and sampling equipment installed to collect surface runoff water.
Figure 1. Layout of surface drainage trial at D & M Evans, Derrinallum showing location of different drainage treatments and the hydraulically isolated catchments.
Major management and experimental activities during 2006
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12 April: Autumn fertiliser applied – 20 kg P/ha as triple superphosphate.
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26 April: All of trial area oversown with “Crusader” Italian ryegrass (Lolium multiflorum Lam.) at 25 kg/ha seed with 80 kg/ha DAP due to very poor persistence of the “Horizon” hybrid ryegrass sown the previous autumn.
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1 May: Installation of all experimental measurement and monitoring equipment completed. This included all pasture, soil, water and meteorological equipment – assessments commenced.
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19 June: Western (experimental) paddocks sprayed by air with 1.5 L/ha of Agtryne MA (Terbutryn 275 g/L + MCPA 160 g/L) and 100 ml/ha of Fastac (Alpha-cypermethrin 100 g/L) for broadleaf weed (mainly thistles) and pasture pest (mainly black headed cockchafer) control.
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Early July: All western (experimental) paddocks crash grazed with commercial mob of sheep following herbicide application.
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14 July: trial ewes weighed, conditions scored, vaccinated and drenched – allocated to and put on trial paddocks (36 ewes/treatment).
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16 July: 100 kg/ha of Urea (47 kg N/ha) applied by air to western (experimental) paddocks.
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28 July: Ewes on trial commenced lambing.
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10 August: Stocking rates on each of the treatments adjusted by adding additional ewe lambs to some treatments. This was done in an attempt to bring standing pasture mass on all treatments back to a common level.
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15 September: Lambs on trial marked. Stocking rates on the different treatments adjusted by removing some of the ewe lambs to bring stocking rates back in line with pasture growth.
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8 November: Lambs weaned. Ewes weighed and condition scored. Lambs weighed and counted. Trial sheep removed from the treatments – animal monitoring for the season concludes.
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5 December: Final pasture measurements for 2006 conducted.
Results and Discussion
Meteorological Monitoring
Rainfall
Total annual rainfall recorded at the trial site for 2006 was only 409 mm compared to the long- term average for Derrinallum of 570 mm (Table 1). This placed the year in Decile 1; that is in the lowest 10% of years indicating a serious rainfall deficiency. In contrast, rainfall for January, February and April was well above average giving a good start to the season. However, from May onwards, monthly rainfall totals dropped dramatically with, except for July, rainfall being in either decile 1 or 2. These results are indicative of the severe drought conditions experienced over much of Eastern Australia during 2006.
Soil temperatures
With frequent frosts occurring over the winter–early spring period, 10 cm depth soil temperatures reached lows of around 5oC some mornings during the June-July period (Figure 2). Such low soil temperatures are likely to have retarded pasture growth over this period, despite there being adequate soil moisture. From early August, soil temperatures started to rise gradually with the mean daily 10 cm depth soil temperature exceeding 10oC by late August. By late November, 10 cm depth temperatures exceeded 25oC some afternoons in response to high daytime air temperatures.
Figure 2. Soil temperature (oC) at 10 cm depth from winter to early summer at the Derrinallum trial site.
Table 1. Monthly rainfall totals (mm), monthly rainfall decile and number of raindays recorded during 2006 at the trial site and at the nearby Bureau of Meteorology recording station compared with the long term averages
Soil Profile Water Content
Soil profile water contents as determined by weekly neutron probe readings to a depth of 100 cm (Figures 3 – 7) indicate that the soil reached maximum wetness in late July. Thereafter, the soil profile dried out steadily during spring at all depths in response to the very low rainfall received over this time. The largest drops occurred at 10 cm depth (Figure 3) in the A1 horizon – this being the zone of most active root growth and hence greatest water extraction. A similar trend, but with lesser water extraction occurred at 20 cm depth in the heavier textured A2 soil horizon (Figure 4). The hump & hollow treatment consistently had lower soil water contents (as indicated by the neutron probe count ratio figures), followed by the control and then the raised bed treatments. This suggests greater water use by the hump & hollow pastures, followed by the control with the raised bed pastures – this trend is particularly apparent at the 20 cm depth (Figure 4) where all three treatments had identical soil water contents in early August but then diverged during spring.
Figure 3. Trend in 10 cm depth soil water content from winter to early summer in the control, raised bed and hump & hollow treatments as measured by neutron probe count ratio.
Figure 4. Trend in 20 cm depth soil water content from winter to early summer in the control, raised bed and hump & hollow treatments as measured by neutron probe count ratio.
Figure 5. Trend in soil profile water content at a range of depths in the control treatment from winter to early summer as measured by neutron probe count ratio.
Figure 6. Trend in soil profile water content at a range of depths in the hump & hollow treatment from winter to early summer as measured by neutron probe count ratio.
Figure 7. Trend in soil profile water content of the raised bed treatment from winter to early summer as measured by neutron probe count ratio.
The neutron probe count ratio data also appears to indicate that soil water depletion by early summer at the 30 and 50 cm depths was lower for the raised bed (Figure 7) than the hump & hollow (Figure 6) and control (Figure 5) treatments. This apparent lower water extraction from the top 10 cm and 20 cm soil horizons by the raised bed pastures compared to the control and particularly the hump & hollow pastures is likely to be explained by nature of the pasture that was established on the respective treatment areas. The raised bed treatment pasture had a much lower plant density, especially of the sown Italian ryegrass than the pasture in the other treatments. There were large areas of bare ground between the fewer, but larger Italian ryegrass plant crowns in the pasture growing on top of the raised beds. Observations over the autumn-winter period indicated that this was due to a poorer initial plant establishment on the beds after the autumn oversowing with Italian ryegrass. In contrast, the pasture growing on the hump & hollow treatment had a greater density of vigorous Italian ryegrass and sub clover with little bare ground.
Water measurements
Perched watertable depth
A series of 1.2 m deep piezometers equipped with automatic data loggers to record the depth below the soil surface of any perched watertable at two hourly intervals were installed in each treatment. Due to the very much below average rainfall received at the site, no perched watertable formed at any time on any part of the trial during the winter or spring of 2006.
Surface water runoff
In each of the western treatment areas, earthworks including mounds, drains and stainless steel barriers were installed to form hydraulically isolated catchments of 2.5 ha in area for the collection of runoff water. Each of these 3 catchments is equipped with a flume at the lowest point to measure the volume and timing of surface water runoff following rain events. Automatic water samplers are connected to each of these flumes to enable the collection of representative water samples for later nutrient analysis.
No surface water runoff events occurred during 2006 due to the very much below average rainfall. Therefore no data on surface runoff or nutrient loss from the different drainage treatments were generated.
Soil Physical Measurements
Soil physical health- Porosity and water holding capacity
A series of 10 intact cores (7 cm diameter) of the 0 – 5 cm depth surface soil were collected from each treatment on 5 July for soil physical condition and porosity assessments.
Marked differences in soil physical condition were found between the soils of the different drainage treatments. Soil bulk density was highest for the hump & hollow treatment at 1.29 kg/L and lowest for the raised beds at 1.17 kg/L, with the control treatment intermediate at 1.19 kg/L (Table 2). Such bulk densities are typical of the light clay soils in the region and should not present any particular problem or limitation in their own right. The higher bulk density of the soil in the hump & hollow treatment may have resulted from the earth moving equipment used to form the beds causing some soil compaction.
Differences in the aeration porosities at 1 kPa and 10 kPa indicate that despite all three treatments having similar total porosities, there were large differences in the pore size distribution of the soils of the different treatments – the control having few large pores, but many small pores while both the hump & hollow and raised beds treatments having more large pores and fewer small pores. Of some concern is the very low 6.5 %V/V aeration porosity at 10 kPa for the control treatment. This figure is well below the 11.5 and 15.7 %V/V values for the hump & hollow and raised bed treatments. It is also less that the widely accepted critical 10% V/V aeration porosity at field capacity (10 kPa) below which pasture growth declines because of reduced root aeration. It is likely that this low aeration porosity for the control has been caused by a number of years of sheep trampling while the cultivation required for the Hump & Hollow and Raised Bed treatments has restored their aeration porosities to levels that are more favourable for plant growth.
Table 2. Effect of drainage treatment on soil physical condition (0 – 5 cm horizon) – soil porosity
The differences in pore size distribution (Table 2), have also had a marked effect on the water holding characteristics of the soils of the three different treatments (Table 3). Most notably, the volumetric soil water content of the control treatment at field capacity (10 kPa) at 43.6% V/V is considerably higher than the 36.1% V/V and 33.5% V/V for the hump & hollow and raised beds treatments respectively. These differences are reflected in the Plant Available Water (PAW, field capacity (10 kPa) less permanent wilting point (1500 kPa)) for the top 10 cm for the soil of each treatment, with control holding 28.5 mm, hump & hollow 19.8 mm and raised beds only 17.8 mm. It is conceivable that such differences in PAW storage capacity will have an impact on pasture growth with the hump & hollow and raised bed treatment pastures likely to run out of soil water earlier than the control treatment.
Table 3. Effect of drainage treatment on soil physical condition (0 – 5 cm horizon) – soil water holding characteristics
Soil stregnth- Trafficability measurements
As outlined in the research protocol for the conduct of the trial (Milestone 1), one of the major aims of the trial is to monitor the impact of the different drainage treatments on trafficability of the soil during the wet conditions of winter – early spring. This was to be assessed using a range of instruments including a penetrometer to measure soil bearing strength and a shear vane to measure the shear strength of the soil at various times over the winter wet period. This would allow the impact of and risk of soil pugging of the different drainage treatments to be assessed and documented. A decline in soil strength and hence the risk of soil pugging occurs when the water content of the top soil exceeds field capacity and begins to saturate.
At no time during the winter or spring did the water content of the top soil exceed field capacity and hence it was pointless taking these measurements during 2006.
Pugging severity assessments
Similarly, the research protocol specified that if any soil pugging occurred as a result of grazing the wet pastures, a number of assessments of the extent and severity of the pugging damage would be done. As no pugging occurred during 2006, such assessments were not undertaken.
Soil Chemical Measurements.
The analytical results of 0-10 cm depth soil samples collected from each of the 3 stratum of the 3 different drainage treatments indicate that overall the soils on the trial site are quite fertile and generally have good chemical health (Table 4).
The Olsen P and Skene K levels in all treatments are in the moderate range and well adequate for near maximum pasture growth. It is notable though that the Olsen P levels in the hump & hollow treatment, although still adequate for good pasture growth are generally lower than for the other two treatments – possibly a result of mixing of top soil with lower fertility soil from deeper in the profile when the beds were formed. CPC – S levels were found to be very high on all treatments, which is common on such clay soil types with impeded drainage.
The soils on the site are however strongly to very strongly acidic which is reflected in some moderate levels of exchangeable Al. These low pH and moderate exchangeable Al levels are not likely to be an issue so long as Al tolerant pasture species are grown on the site. However if more Al sensitive species such as phalaris are to be sown, then the application of lime to raise the pH may well be beneficial. Predictably, given the poor drainage of the soil type and the site, the Electrical Conductivity (E.C.), Electrical Conductivity of the saturated extract (ECe) and Total Soluble Salt ( T.S.S.) figures are elevated indicating that the soil is slightly saline. However, provided salt sensitive plant species are not grown, these higher salinity levels should not be an issue. The Exchangeable Cation (Exch Ca, Mg, Na & K) results indicate that the soils are magnesic and likely to have some structural problems. The Ca:Mg ratio at around 1.2 is low and well below the accepted desirable ratio of > 2.0. This is reflected in all the samples having moderate dispersion of remoulded aggregates, but not of the dry aggregates. This suggests that the soils are likely to disperse and suffer from structural breakdown when mechanically disturbed, such as if pugged or cultivated. The data also suggests that this soil is likely to have beneficial responses to gypsum applications, especially if cultivated for cropping.
Table 4. Chemical composition of soils (0-10 cm) collected from each of 3 stratum in the raised bed, control and hump & hollow treatments in July 2006
Raised bed soil profiles
In order to determine the effect of sheep grazing and trampling on the structure and longevity of raised beds under grazing, 12 permanently marked monitoring points on different areas of the raised bed paddock were established in July 2006. At each of the monitoring points, the profile, or shape and dimensions of the bed was determined and recorded using a “profile meter”. This “profile meter” consists of a 2 m wide wooden frame with a series of 40 steel pins at 5 cm intervals, with legs at each end placed in the furrows either side of the raised bed. The height of each pin above the wooden frame is measured enabling the profile of the bed to be recorded. Typical raised bed profiles as at July 2006 are illustrated in Figures 8(a) and 8 (b).
Figure 8. Raised bed profile in a). Position 2 –bed 10 east; and b). Position 11 – bed 50 west.
The raised beds in the eastern parts of the trial area (closest to the outlet flumes), are typically lower with the depth of the furrows either side of the beds being in the order of 6 – 12 cm deep (Figure 8 a). In contrast the raised beds in the western end of the trial area are higher (12 –16 cm), with steeper sides (Figure 8 b). By superimposing the profile of the raised beds at each spot at the start and finish of each year, the wearing away of the raised beds can be monitored. This end of year profile assessment was not conducted in the summer of 2006 due to the dry winter. The next assessment is planned for autumn 2007.
Pasture Measurements
Pasture yields and growth rates
The control treatment produced higher total herbage DM yields (7.61 t DM/ha) for the year than either the hump & hollow (7.05 t DM/ha) or raised beds (4.81 t DM/ha) treatments (Table 5). Pasture net accumulation rates peaked in the early September period with daily rates of 95 kg DM/ha.d-1 for the hump & hollow treatment and 88 kg DM/ha.d-1 for the control treatment. Pasture net accumulation rates were consistently lower for the raised bed treatment right across the growing season with a maximum of 68 kg DM/ha.d-1 during the peak early September period. At other times, the pasture net accumulation rates for the raised beds were considerably lower than for the other two treatments, often only being half. Observations after sowing and during the growing season suggest that this may be due inpart to a much poorer establishment of the oversown Italian ryegrass on the raised beds compared with the control and hump & hollow pastures. The raised bed pastures typically had a lower density of ryegrass crowns, often with large bare areas around them. Despite an apparent adequate early establishment of Italian ryegrass seedlings in the autumn, there appeared to be a high mortality of young seedlings over the dry winter on this treatment.
The greater herbage yields for the control compared to the hump & hollow pasture from early October onwards may have resulted in part from the greater Plant Available Water in the topsoils of the Control treatment noted earlier.
Table 5. Herbage DM yield (t DM/ha) and net accumulation rate (kg DM/ha.d-1) of pasture growing under different surface drainage treatments during the winter and spring of 2006
The herbage DM yield and net accumulation rates for the raised beds treatment (Table 5) were estimated from pasture assessments from both the top of the beds and pasture growing in the furrows between the beds (Table 6). The furrows grew only marginally more pasture over the growing season; 5.06 compared to 4.77 t DM/ha for the top of the beds. From mid September onwards, the furrows produced consistently higher DM yields and net accumulation rates than the top of the beds. This difference was most pronounced in November as drought stress became severe.
Table 6. Herbage DM yield (t DM/ha) and net accumulation rate (kg DM/ha.d-1) of pasture growing on top of the beds and in the furrows between the beds in the raised bed treatment area during the winter and spring of 2006
Herbage nutritional value
At each pasture DM yield assessment time, the nutritive value of herbage from a bulked sample of standing pasture collected to ground level from under the exclusion cages in each treatment was determined by FeedTest, Hamilton. The metabolisable energy (ME) contents (MJ/kg DM) were similar for all treatments over time, with the exception of the pasture grown in the furrows of the raised bed treatment (Figure 9). Metabolisable energy levels reached a high of 13.5, 13.3 and 13.9 MJ/kg DM for the control, hump & hollow and top of the raised bed treatments respectively in late August. At this same harvest, the ME of the pasture growing in the furrows of the raised bed treatment was lower at 12.2 MJ/kg DM. At each successive harvest thereafter, the pasture ME declined gradually reaching lows of 9.6 – 10.1 MJ/kg DM by early December. The ME of the furrow pasture at this time was considerably lower at 7.8 MJ/kg DM. The crude protein (CP) (%DM) content of the pasture also followed a similar pattern as the ME content (Figure 10). Crude protein contents peaked at the late August harvest at levels of 28 – 31% in response to the application of 47 kg N/ha as urea in mid July. At this same harvest, pasture from the raised bed furrows had a marginally lower CP content of 25.5%. Crude protein levels then fell rapidly during the spring period, reaching lows of 8.4% (control) to 10.6% (hump & hollow) by early December.
Figure 9. The metabolisable energy content (MJ/kg DM) of pasture growing on the control, hump & hollow and raised bed treatments over the 2006 growing season.
Figure 10. The crude protein (%DM) content of pasture growing on the control, hump & hollow and raised bed treatments over the 2006 growing season.
Figure 11. The neutral detergent fibre (%DM) content of pasture growing on the control, hump & hollow and raised bed treatments over the 2006 growing season.
Figure 12. The water soluble carbohydrate (%DM) content of pasture growing on the control, hump & hollow and raised bed treatments over the 2006 growing season.
Neutral detergent fibre (NDF) levels were lowest in the late winter-early spring period (Figure 11). In late August, the raised bed tops had the lowest NDF levels at 34.9% and the raised bed furrows the highest at 40.4 %. NDF levels then rose during the spring period as the pastures matured with the raised bed tops again having the lowest NDF level at the early December harvest of 54.9% and the raised bed furrows the highest at 64.7%. The water soluble carbohydrate (WSC) content of herbage displayed the greatest differences between treatments (Figure 12). The raised bed tops consistently had the highest WSC contents across the growing season with levels of over 16% during the spring period. The raised bed furrows peaked at 12.7% in early spring but then dropped rapidly over the spring period to a low of 7% in early December – a value half that of next lowest treatment. The hump & hollow treatment WSC levels considerably lower than all other treatments over the winter period, but levels then rose to around double that in the mid to late spring period.
Pasture botanical composition
The pastures in all treatments were dominated by the over-sown Italian ryegrass throughout the 2006 growing season (Figure 13). This ryegrass contributed at least 60% of the DM yield of the pastures for all except the early winter (after an autumn sowing). Self-regenerating subterranean clover (Trifolium subterraneum L. Ssp. Yanninicum. cv. Yarloop) was the second most abundant species for most of the growing season. This was especially so in the hump & hollow treatment (Figure 13 b) where it contributed up to 30% of the DM yield of the pasture in the early spring period. At this same time the Yarloop sub clover contributed 18% of the control (Figure 13 a) DM yield, 12% of the raised bed tops (Figure 13 c) and only 8% of the raised bed furrow (Figure 13 d) DM yields. Also of significance was the contribution of the volunteer grasses, labelled as “others” in Figure 13. These volunteer grasses consisted predominantly of barley grass (Hordeum vulgare L.) and soft brome (Bromus mollis L.) and silver grass (Vulpia bromoides ) and were particularly obvious in the control treatment (Figure 13 a) where by late spring they were contributing 25% of the pasture DM yield. The hump & hollow and raised bed treatments had only relatively small amounts of these volunteer annual grasses.
Animal performance
Sheep numbers and stocking rates
The requirement to over-sow all the trial areas during the autumn with Italian ryegrass following the poor ryegrass persistence during the previous summer meant that the trial was not able to be stocked with the trial flocks until the 14th of July. Initially, 36 in-lamb ewes were placed on each treatment. This number was arrived at in consultation with the “Grain & Graze” program managers and the collaborating farmer. It was designed to give a nominal stocking rate of 5 ewes/ha, a figure that was thought to be appropriate and safe for the conditions. During mid August, visual observations suggested and pasture meter measurements confirmed that differences in the amount of standing pasture between the treatments were occurring. The control treatment had considerably more standing pasture than both the hump & hollow and raised bed treatments.
These differences were attributed to:
a. when accurately surveyed, the total area of each treatment was found to be different – the total area of the control treatment was found to be 2.0 ha greater than the hump & hollow treatment (Table 7).
b. the control treatment had an observed higher pasture density over the winter period as a result of the greater amount of volunteer grasses in this treatment.
Figure 13. Botanical composition (% DM) of pastures of a). control, b). hump & hollow, c). raised bed – tops, and d). raised bed – furrow treatments during the winter and spring of 2006.
In collaboration with David Watson (“Grain & Graze” consultant), feed budgeting was used to estimate the stocking rate required to bring standing pasture back to a common level between the treatments. Some 62 and 11 rising 1 year old ewe lambs were added to the ewe flocks in the control and raised bed treatments respectively on the 20 August (Table 7). The number of these additional ewe lambs were further adjusted at marking time (15 September) in light of the pasture on offer and observed growth rates on each of the treatments.
Effective stocking rates for the period from lamb marking to weaning (15 September to 8 November) were the equivalent of 5.2, 5.4 and 4.3 ewes/hectare for the control, hump & hollow and raised bed treatments respectively (Table 7).
Table 7. Number of sheep run on the control, hump & hollow and raised bed treatments during the 2006 experimental period, the area of each treatment and resultant stocking rate equivalent (ewes/ha)
Sheep liveweights and condition scores
The mean liveweight of the ewe flocks allocated to each of the trial treatments on 14 July were 67.4, 67.9 and 66.6 kg for the control, hump & hollow and raised bed treatments respectively (Table 8). Mean ewe condition scores were similar for all treatments at 3.6 to 3.7 confirming that the ewes allocated to each treatment were very similar at the start of the trial. By weaning (8 November), differences in mean flock ewe liveweight had developed between the three treatment flocks. Ewes from the hump and hollow treatment had the highest mean liveweight at 81.7 kg, the raised bed ewes were 77.7 kg whilst the control flock had the lowest mean liveweight of 75.0 kg. Ewe condition scores were very similar though at either 3.7 or 3.8 for all treatments.
Table 8. The liveweight (kg) and condition score of ewes at the start of the trial (14 July) and at weaning (8 November); number of lambs weaned and their liveweight (kg) (8 November) from the Control, Hump & Hollow and Raised Beds treatment areas
The number of lambs weaned off each treatment on 8 November were 30, 44 and 33 for the control, hump & hollow and raised bed respectively (Table 8). Despite ewes that were scanned as carrying only a single lamb being allocated to the trial, a number of sets of twin lambs were born in the hump & hollow and raised beds flocks. This resulted in 44 and 33 lambs being weaned off the hump & hollow and raised bed treatments compared to the 30 off the control treatment. Lamb weights at weaning were very similar between treatments at 37.2, 37.9 and 37.2 kg/head for the control, hump & hollow and raised bed respectively.
General Discussion
Unfortunately, the very low rainfall totals received at the trial site during the winter and spring of 2006 resulted in the soils staying relatively dry without the periods of water logging normally experienced in most years in this area. As a result, no runoff occurred from the plots at all during the year. There was no surplus water present to be removed by the artificial surface drainage systems installed in the hump & hollow and raised bed treatments; - these systems being designed to speed the removal of excess water from the pasture, therefore reducing the severity and duration of waterlogging of the pasture. As the soil water contents did not exceed field capacity at any time during the year, the soils retained their bearing strength and did not suffer any pugging damage. Therefore, a number of the aims of the trial were not able to be met during the 2006 experimental period. In particular, the effects of surface drainage on; waterflows off the drainage treatments, waterlogging severity and duration, and the trafficability of the pasture and soil under the different drainage treatments.
However, the 2006 experimental period was able to provide some valuable data and learnings on the effect of the installation of the different surface drainage systems on soil physical condition and health, and on pasture production responses and issues for the different surface drainage systems. Also, experience gained by operating the trial during 2006 identified a number of areas where improved experimental methodology can be implemented in the 2007 experimental period.
One key finding was the effect that the installation of the hump & hollow and raised bed surface drainage systems had on soil physical condition and health. The surface 0-5 cm depth soils of both the hump & hollow and raised bed treatments were in physically much better condition than soils from the control treatment. The low aeration porosity of the control at 10 kPa (field capacity) of 6.5% is of some concern. It is well below 10% - the commonly accepted critical level below which plant growth starts to be restricted due to poor root aeration and penalties in terms of reduced plant growth would be expected. In contrast, both the hump & hollow and raised bed treatments with aeration porosities (10 kPa) of 11.5 and 15.7 % respectively are favourable for plant growth and are very unlikely to restrict plant production. This result is also consistent with earlier findings in south west Victoria that soils on raised beds used for cropping were found to have better soil physical health than comparable soils without drainage. These improved aeration porosities for the raised bed and hump & hollow treatments may well be a result of the soil cultivations required to form these surface drainage treatments. Therefore, an important role of this trial will be to monitor changes in soil aeration porosities of the different treatments into the future to determine the longevity of these improved soil aeration porosities on the two drained treatments.
The improved soil physical health of the two drained treatments did not however appear to be expressed in terms of improved pasture production over the control treatment. Part of this may have been a result of corresponding reduced water holding capacity, as reflected in the plant available water data, of the drained soils. With estimated reductions in plant available water in the top 10 cm of the soil of 10.7 mm and 8.7 mm respectively for the raised beds and hump & hollows compared to the control, reduced water availabilities bringing about earlier onset of drought stress may have reduced pasture growth rates in the two drained treatments.
The raised bed treatment clearly had lower pasture and animal productivity (reflected in the lower stocking rate) than either the control or the hump & hollow treatments. Field observations over the trial period suggest that this may in large part be due to the very much weaker and more open pastures that established on this treatment. Despite having what appeared to be quite a satisfactory initial establishment of the Crusader ryegrass after the autumn over-sowing, there was observed to be quite a high mortality of young ryegrass seedlings on the raised beds due to water stress during the winter-early spring period. This is likely to have been exacerbated by the “improved drainage” of the beds reducing the capture of what rainfall there was, and the reduced water holding capacity of this soil to store this water. As a result the pastures on raised beds had much more bare space with lower plant densities.
Effectively during 2006, a different pasture type developed on each of the three different treatments – a factor which is likely to have influenced the results of the trial, and if possible should be avoided for the 2007 growing season. The raised bed treatment as discussed above suffered from poor establishment of the over-sown ryegrass, which hopefully can be avoided with more favourable seasonal conditions. The control pasture however had areas with a high proportion of carryover volunteer annual grasses which contributed to the growth and yield of this treatment. It is recommended that as part of the over-sowing of the pastures on the trial area that will be required in the autumn of 2007, that the whole area be sprayed with a knockdown herbicide to attempt to establish more uniform pastures across the treatments.
The results from the 2006 growing season indicate that in dry years, surface drainage systems do not improve either pasture or animal production compared to the undrained control treatment. Further, it was found that the use of Raised Beds was infact detrimental to both pasture and animal production. This may however be quite different in wet years with periods of significant waterlogging.
Extension Activities
Due to the very dry seasonal conditions resulting in the lack of any waterlogging or runoff from the site, there was limited opportunity for extension activities to be conducted as part of the project during 2006.
The major extension activities conducted were in association with the Grain and Graze National Forum held in Geelong during August 2006. On Monday evening 14 August, Graeme Ward and Tim Johnston manned a poster and static display at the Corangamite/Glenelg Hopkins Grain and Graze Region trade display for forum delegates at the Mercure Hotel, Geelong. As part of the Forum’s field tour program, the delegates visited the Derrinallum trial site on Wednesday afternoon the 16th of August. At the site presentations explaining the design and purpose of the trial were delivered by Graeme Ward and Tim Johnston, and despite very strong winds, led an inspection of the trial site.
Some limited farmer awareness publicity was conducted during the winter of 2006 with two short articles on the purpose of the trial being published in DPI’s column in the rural section of Warrnambool’s “The Standard” newspaper during the winter of 2006.
