Manage recharge and salinity – South West Victoria (Lower)

The issue – recharge and salinity

There are at least 51,000 hectares of salt-affected land in the combined Glenelg-Hopkins and Corangamite region (Victorian Resources Online). This has led to the loss of pasture production (especially in salt sensitive pasture species, such as clover and lucerne) in affected areas. This poor plant growth results in bare ground exposed to wind and water erosion and the invasion of salt tolerant weeds, such as barley grass. Nutrient imbalances or deficiencies in affected soil further reduce plant growth. High salt levels lead to soil structure decline and a range of environmental problems, such as saline waterways that affect aquatic life.

Low pasture production and spiny rush are typical of salt discharge areas in south-west Victoria.
Low pasture production and spiny rush are typical of salt discharge areas in South West Victoria.

The cause – understanding catchment processes

The key to developing sensible dry land salinity management strategies lies with understanding how landscapes and groundwater processes function to cause salinity.

Over the past few decades there has been a focus on the control of groundwater recharge, as this was thought to be the primary cause of salinity. This approach has advocated the broad-scale replacement of low productivity pastures dominated by annual species with pastures based on perennial grasses and legumes as a means of reducing groundwater recharge and controlling dry land salinity.  So land management has focused largely on attempts to reverse changes in the hydrological balance following agricultural development. Much effort towards understanding the relationships between soils, rainfall, vegetation and farming systems has aimed to identify productive land management practices that use more rainfall, whilst limiting runoff and groundwater recharge.

For example, eighteen groundwater flow systems (GFS) have been delineated in the Glenelg-Hopkins CMA region, and seventeen in Corangamite CMA region. They fall into three categories:

  1. Local flow systems – groundwater flows over distances less than 5km
  2. Intermediate flow systems – groundwater flows over distances 5 to 30km , and
  3. Regional flow systems – groundwater flows over distances more than 50km

We now know that ameliorating salinity is more than simply recharge control. Salinity management requires an integrated approach to landscape water control. Each catchment is unique so it cannot be assumed that we can simply translate our understanding of one particular landscape to others. The manifestation of salinity in each region is linked intimately to the groundwater processes prevailing within that region (such as size of the aquifers, how readily they transport groundwater, and their storage capacity), and relationships with regional landscapes. Only when these relationships are understood can informed salinity management planning occur.

Importantly though, there is now a recognition that effective recharge control is generally difficult to achieve in the large regional groundwater flow systems, such as the Basalt Plains. These systems require regional scales of adoption for recharge control to be effective; and the outcomes may not be delivered for many decades due to the built-in inertia and slow responsiveness of these systems. In such circumstances, stabilising and/or increasing the productivity of groundwater discharge areas becomes even more important. (Refer to Managing saline discharge areas, below)

To better understand the mechanisms that drive dry land salinity in the region go to Dryland salinity on the basalt plains and papers by Dahlaus et al.

The options – managing recharge

Addressing recharge with summer active perennials

Pastures for sheep and cattle in southern Australia have traditionally been based on either perennial ryegrass or phalaris with annual subterranean clover.  Almost all their growth occurs from the autumn break in mid-April until pastures dry off in mid-December, and they respond only to large rainfall events during summer. Furthermore, they have little capacity to extract water below a depth of 1.4 m.

The three criteria for achieving recharge reduction with summer actives

Results and modelling from EverGraze research at Hamilton indicated that there are three characteristics required for a pasture to the control the groundwater recharge that drives salinity. These are;

  1. Summer activity;
  2. Persistence under grazing at high stocking rates (maintaining density); and
  3. Deep rootedness.

Pasture plants that are commercially available but with greater summer growth than perennial ryegrass include summer active tall fescue, lucernechicory, and kikuyu. These remain green through the summer period and can extract water to a greater depth than annual species. Higher water use during summer and deeper rooting characteristics suggest they reduce leakage below the root zone (recharge). For example, lucerne roots can grow to three metres deep, drying the soil profile to at least five metres (greater depth than all annual and most perennial species). In the Triple System at Hamilton EverGraze Proof Site (Figure 1), lucerne reduced recharge by 80 mm/yr compared to ryegrass pastures on well drained crests, and summer active tall fescue on clay flats reduced recharge by up to 60 mm/yr compared to ryegrass pastures.

Lucerne is the only plant that fulfils the three criteria for recharge control (Table 1). Chicory controlled recharge for the first three years of the Hamilton experiment but then density declined due to lack of plant persistence. Summer activity in the Triple system also had significant benefits for reducing supplementary feeding costs in years with a failed spring, and providing opportunities for finishing lambs in good seasons, at no expense to winter feed. For further information, see the Hamilton EverGraze research message Lucerne reduces risk, provides options for livestock and prevents salinity.

Table 1: Pasture species characteristics relevant to recharge control

  Summer activity Deep plant roots Persistence
Lucerne
Chicory
PRG Fitzroy
Kikuyu
Fescue
PRG Banquet

Figure 1. Triple system at Hamilton EverGraze Proof Site showing rooting depth of lucerne, tall fescue and perennial ryegrass.
Figure 1. Triple system at Hamilton EverGraze Proof Site showing rooting depth of lucerne, tall fescue and perennial ryegrass.

Selecting the right summer active

Although lucerne appears to be the most effective pasture species for managing recharge, it is suited only to areas that are well-drained and with low soil acidity and aluminium.  Conversely, tall fescue is tolerant of waterlogged areas but is less likely to persist on the gravelly crests. Selecting the right combination of plants must also consider the needs of the livestock production system, and individual management requirements of each plant variety.  The management of summer active perennials will also influence the degree to which they are able to control recharge.   For example, rotational grazing of lucerne is required to enable it to persist at sufficient densities to extract the stored winter surplus during the following summer.

Further information on selecting pastures for place and purpose can be found under Feedbase Options and on the Hamilton EverGraze Right Plant, Right Place, Right Purpose, Right Management page.

In practice, the actual impact on recharge due to changing grazing systems is somewhat limited by the landscape itself and the potential for adoption of new grazing systems. In a modelling study of the Wannon Catchment in SW Victoria the greatest reduction in recharge was therefore in those landscapes with the largest proportion of “crest” land on which lucerne could be established. This was in the Casterton landform zone (with approximately 50% crests) where recharge was reduced from 125mm/year under current practice to 90mm/yr with half the crest areas sown to lucerne.

The water use trade-off with farm dam levels and stream flow

A second limitation of summer-active pastures is that both surface runoff and groundwater recharge decrease.  In many areas the livestock enterprise relies on surface runoff to fill farm dams used for stock water.  In other areas such as the basalt plains, underground water is the most commonly-used source of stock water, but some recharge is necessary to maintain the resource.  Therefore, while there is a need to reduce recharge from the overall landscape, surface runoff and groundwater recharge should continue in some parts of the landscape to fulfil stock water and environmental requirements as well as community expectations of stream flow.  See EverGraze systems will reduce recharge in the Wannon catchment for details of the impact of lucerne on farm dams and streamflow.

Addressing recharge with deep rooted winter active perennials

Although they may not fully control recharge, well-managed deep rooted winter active perennials will stay productive later into the growing season, resulting in a higher water use than annual-dominant pastures. Late flowering perennial ryegrass and summer active tall fescue on the valley floors of the EverGraze Proof Site at Hamilton used more water than the failed kikuyu pasture which was dominated by silver grass and sub clover. At the Broadford Grazing Experiment in central Victoria (mean annual rainfall 625mm) a dense stand of phalaris/sub clover which was rotationally grazed to achieve persistence of the perennial, also used significantly more water than a set stocked pasture dominated by capeweed and sub clover.  It is likely that the higher water use in this scenario was a result of the higher perennial density, rather than the rotational grazing, as other studies have not shown a difference in water use resulting from management of perennial pastures of similar composition.

Addressing recharge with shrubs at the break of slope

As discussed in the section Understanding catchment processes, in local flow systems groundwater may flow less than 5km with excess water accumulating in the lower parts of the landscape where it mobilises salt. Preventing the movement of water down slope is one way to mitigate this form of salinity. One option to achieve this is to establish shrub belts along the contour to create dry soil buffers that are capable of absorbing water flowing down slope as either surface flow or sub surface flow across the soil A/B horizon interface.

Whilst data specific to southwest Victoria is lacking, the Wagga Wagga EverGraze Proof Site tested the effectiveness of shrub belts at break of slope and concluded the following:

  • The shrubs used more water than annual pastures and therefore created a small dry soil buffer in the area where they were planted.  However, the area sown to shrubs was not large enough to significantly reduce soil moisture at the foot of the slope, ie recharge control.
  • Lucerne and the shrubs used similar quantities of water, and because lucerne was sown throughout the paddock, it had a significant effect on soil water at the foot of the slope.  That is, lucerne pasture without shrubs would provide recharge control similar to lucerne with shrub belts.
  • Shrubs had no impact on pasture growth. So soil moisture in the pasture areas between the shrub belts was largely unaffected and therefore had no impact on pasture growth, but no recharge control either.
  • The evidence from the EverGraze Proof Site does not support the use of shrub belts for recharge control in environments such as those at Wagga Wagga. However, it does not mean that farmers should not plant shrubs for other reasons such as discharge management, livestock shelter and biodiversity.

The issue – saline land

In addition to information provided below, Saltland Genie uses the latest knowledge and tools for salt-land management from the Sustainable Grazing on Saline Land initiative to compare the pros and cons of 11 possible options to manage saline land for a unique farm scenario. The tool also provides case study examples for what has worked for others.

A saline soil is one with an accumulation of free salts at the soil surface and/or within the profile affecting plant growth and/or land use. These areas typically have carrying capacities of less than 5 DSE/ha, and are dominated by undesirable plants such as barley grass and spiny rush. Yet with appropriate management, carrying capacities on some saline areas can be increased 2-4 fold. Furthermore, stock can gain weight during summer, because high water tables allow pastures in saline areas to remain green while other pastures are dry.

Plants may face several challenges in saline soils: salinity (salt in the soil water), waterlogging (lack of oxygen for root function) and/or periodic flooding (water above the soil surface). A combination of them is particularly difficult.  For example, plants that actively exclude salt from the root surface in well-aerated soils cannot do this when the soil is waterlogged, because the roots don’t have sufficient oxygen.

Farmers also face challenges in managing saline areas. For example;

  • Animal welfare may be compromised because saline areas can have surface water for up to three months each year.
  • Vehicle access may be limited for long periods, reducing options for cultivation, sowing and herbicide application.
  • Many saline areas are small (<5 hectares), and it may not be worthwhile to manage them for production.

Measuring salinity

EC (electrical conductivity): Salinity is measured by the ability of water to conduct an electric current. Increasing salt in water or soil increases conductance. Distilled water has an EC of less than 0.0001 deciSiemens per meter (dS/m), and seawater 55 dS/m. Some laboratories report conductivity in different units, and conversions are shown in Table 1.

EC 1:5 is reported as part of standard soil analyses. It is the most routine measurement of salt content, but is affected by any particles in the water suspension including dispersed clay and organic matter.

ECe is the electrical conductivity of water within the soil when the soil is saturated with water, and is thus a more direct measure of soil salinity. However it is a more difficult procedure and not carried out routinely. Approximate conversions between EC 1:5 and ECe are shown in Table 1.

EM: Electromagnetic signals provide an indication of where a salt problem is likely to arise in the future, and is useful in fencing saline areas. An EM38 held horizontally detects salts in the top 40 cm, and if held vertically 1 m. An EM31 in horizontal mode senses the top 2 m, and vertically the top 6 m.

Table 2: Conversion table for salinity units

To convert to multiply by
millisiemens per centimetre (mS/cm) decisiemens per meter (dS/m) 1
millisiemens per metre (mS/m) decisiemens per meter (dS/m) 0.01
microsiemens per centimetre (µS/cm) decisiemens per meter (dS/m) 0.001
EC 1:5 sand ECe 14
EC 1:5 loam ECe 11
EC 1:5 clay ECe 8

Salinity varies through the year

Values of EC 1:5 and ECe change about three-fold during the year. Salt concentrations in the topsoil are highest at the end of summer because soil evaporation concentrates salts toward the surface. Salinity drops during winter as rainfall flushes the salts deeper, thus winter-growing plants avoid the highest levels of salinity. The best time to measure soil salinity is between November and March, because it is relatively stable, and indicates the highest levels the plants will be exposed to.

Recognising dry land salinity

Soil salinity can be determined precisely by soil tests or subjectively through observation of salt-tolerant plant species.

A paddock walk is a quicker and cheaper way of assessing salinity than soil testing or electromagnetic (EM) surveys. The presence of salt indicator species allows classification into a 3-class system, which is the first step in deciding management options.

Salinity classification

Plant indicator species can be used to classify salinised land as follows:

Class 1 – mild salting can be hard to identify and is characterised by stunted pasture growth. Salt sensitive species such as sub-clovers disappear. No salt crystals or bare patches can be seen. Soil test salinity (ECe) 2–10 dS/m

Class 2 – Where there is moderate salting, patches of bare ground appear, salt-sensitive species disappear and more salt-tolerant species become dominant. Soil test salinity (ECe) 10–25 dS/m.

Class 3 – in cases of severe salting, only the most salt tolerant species remain. Large areas of bare ground will be apparent, often with salt stain visible during dry periods. Loss of topsoil from the site is common. Soil test salinity (ECe) 25–40 dS/m.

Class 2 salinity
Class 2 salinity

Class 3 salinity
Class 3 salinity

Indicator species

Buckshorn plantain (Plantago coronopus) is a low-growing introduced perennial tolerant of flooding, waterlogging and Class 2 and Class 3 salinity. It is a good indicator of salt stress, having leaves of a dull grey-green colour at low salinity and dark red at higher salinity. Sheep will graze buckshorn plantain.

Yellow buttons (Cotula coronopifolia) are introduced annual plants tolerant of Class 2 and Class 3 salinity, flooding and waterlogging. They colonise disturbed areas and are readily eaten by sheep when in the vegetative phase.

Sea barley grass (Hordeum marinum) is an introduced annual grass tolerant of Class 1 and Class 2 salinity, but it also grows widely in non-saline areas. It is eaten by sheep when in the vegetative phase.

Buckshorn plantain
Buckshorn plantain

Yellow buttons
Yellow buttons

Sea barley grass
Sea barley grass

Salt couch (Sporobolus virginicus) is a summer-growing native perennial couch grass, tolerant of Class 2 and Class 3 salinity. It is green during summer, readily eaten by sheep, and its stolons are able to grow across scalded areas.

Native puccinellia (Puccinellia stricta var perlaxa) is a perennial grass able to colonise scalded areas of Class 2 and Class 3 salinity. Its flower head has more widely spreading branches than the introduced Puccinellia ciliarta. Its feed quality and preferred growing conditions are similar to its introduced cousin.

Salt couch
Salt couch

Native puccinellia
Native puccinellia

For more information on salt tolerant plants in South West Victoria go to Soil-salinity tolerant plants of the western Victorian region and Water spotting soil salting.

The options – pasture management for saline land

Separate fencing of saline land is the first step to improving its growth and utilisation, because unless fenced separately, sheep tend to overgraze saline land.  The next step is to either manage the native and volunteer species, or sow a new pasture.

Native pastures for saline land

Better management of existing volunteer plants including natives on saline land is worth serious consideration when desirable plant species are already present and

  • saline areas are too small to justify sowing and separate management
  • salinity is mainly Class 2 or 3
  • the landholder has an interest in native pastures

The saline areas should be fenced separately, and grazed as part of the overall farm rotational grazing. Deferment of grazing in early summer can be used to thicken up native species that flower at that time of the year. Summer weight gains of 60 g/day between December and March have been recorded on volunteer pastures that consisted of buckshorn plantain and salt couch. This was achieved on Class 2 saline land, but at stocking rates of only 4 sheep/ha. Sowing of native herbaceous species is not yet a practical option at the paddock scale, but research into low-cost methods of propagation is continuing.

Introduced species for saline land

Grasses

Tall wheatgrass (Thinopyrum ponticum) is a productive perennial grass tolerant of Class 1 and Class 2 salinity. It has been the dominant sown pasture species on saline land in south west Victoria. The current variety Dundas, was selected for improved leafiness and digestibility over the previous variety, Tyrell.

Tall wheat grass pasture
Tall wheat grass pasture

Tall wheatgrass seedhead
Tall wheatgrass seedhead

Saltland Genie case study farms in Hamilton (Michael Blake) and the Victoria Valley (Les Payne) demonstrate the significant production benefits from establishing tall wheat grass in saline and waterlogged soils.  Michael Blake found that carrying capacity could be increased from 2.5 DSE/ha to 15.5 DSE/ha on tall wheat grass compared to volunteer pastures.  Les Payne established a 35ha area of Class 1 and 2 salinity to tall wheatgrass. Green feed between January and April allowed pregnant ewes to maintain weight with virtually no supplementary feeding. In an EverGraze case study, Peter Hayes from Hamilton also explains how tall wheatgrass has carried up to 20 DSE/ha on his saline waterlogged soils.

Tall wheatgrass weed risk and managementWhile tall wheatgrass is highly suitable as a hedgerow grass species or for planting in salt-affected areas, a weed risk assessment undertaken by the Future Farm Industries CRC has identified tall wheatgrass as having a high environmental weed risk for Victoria through its capacity to invade and impact on wetlands. For this reason, the CRC does not recommend the planting of tall wheatgrass in Victoria. Agriculture Victoria considers that because tall wheatgrass is already widely distributed and has production and animal welfare benefits, its continued planting is appropriate, provided that the following practices to reduce the risk to native vegetation are adopted. To minimise the risk of tall wheatgrass spreading into areas where it is unwanted, hedgerows should be grazed in January and February to remove immature seed. Areas surrounding tall wheatgrass should be sown to competitive species such as perennial ryegrass and phalaris to reduce the chance of spread outside the sown area. Hedge areas should be located well away from waterways or natural wetlands, not only to reduce the chance of spread, but because these areas are often too wet for lambing and can harbour foxes.

Puccinellia (Puccinellia ciliata) is a fine-stemmed perennial grass tolerant of Class 1 and Class 2 salinity, and more tolerant of flooding than tall wheatgrass. It is easily established and grows mainly during winter and spring, but will stay green during summer if there is subsoil moisture.

Tall fescue (Festuca arundinacea) is a productive perennial grass tolerant of Class 1 salinity. Saline areas should be sown to varieties that are summer-active.

Puccinellia
Puccinellia

Tall fescue
Tall fescue

Legumes

Balansa clover (Trifolium michelianum) is an annual clover tolerant of Class 1 salinity. It has good tolerance to flooding because its stems are hollow, allowing oxygen to move down to the roots when the plant is partially submerged. The most popular variety, Bolta, flowers in mid November.

Persian clover (Trifolium resupinatum) is an annual clover tolerant of Class 1 salinity similar to Balansa, but is more tolerant of flooding. Cultivar Nitro flowers about 2 weeks later than the Bolta variety of Balansa.

Strawberry clover (Trifolium fragiferum) is a perennial legume tolerant of Class 1 salinity and waterlogging, but prefers alkaline soil. It is a weak seedling, but with sufficient moisture stays green through the summer.

Balansa clover
Balansa clover

Persian clover
Persian clover

Strawberry clover
Strawberry clover

Sowing and establishment of introduced species on saline land

The first step in sowing a pasture on salt-affected land is to control annual grasses by spraying in October. A total kill is not necessary, because summer-growing perennials such as salt couch and buckshorn plantain will not compete strongly with the new pasture, and their transpiration will reduce salts rising to the surface over summer. Late spring is the best time to determine the severity of salting by observing indicator species. Two soil samples (0–10 cm) should be collected – one from a good area of the paddock and one from a poor area – and analysed for EC, pH, Olsen phosphorus and available potassium.

Saline sites are variable so a mixture of pasture species should be purchased. Suggested sowing rates are shown in Table 2. The pasture mix should be sown in late March or April after opening rains. If cultivation is required prior to sowing, the length of fallow should be minimised to reduce salts rising to the surface, and the number of passes minimised to reduce damage to soil structure. Spraying for red-legged earth mite is necessary to ensure successful legume establishment.  If there have been no sowing rains by late April, the pasture can be sown dry. However, dry-sown pastures have a higher proportion of unsown “weeds” than where cultivated or treated with herbicide between the autumn break and sowing. Alternatively, sowing can be delayed until spring.

Table 3. Sowing rates for pastures on saline land

Salinity class Class 1 Class 2 Class 3
Summer-autumn  ECe (dS/m) 2-10 10-25 25-40
Year 1      
Tall fescue (kg/ha) 15 - -
Tall wheatgrass (kg/ha)*see tall wheatgrass weed risk and management 7 10 15
Puccinellia (kg/ha) 3 4 8
Strawberry clover (kg/ha) 2 3 -
Balansa clover (kg/ha) 0.5 1 -
Persian clover (kg/ha) 0.5 1 -
Year 2      
Balansa clover (kg/ha) 1-2
Persian clover (kg/ha) 1-2

There are important differences in the agronomy of land at different salinity levels:

Class 1: Weed control is critical for these areas, and cultivation or a second spraying may be required between opening rains and sowing. Balansa and Persian clover will be strong competitors to the sown grasses and should be sown at a low sowing rate. Alternatively, these legumes can be drilled in or spread with fertiliser in the following year, once the sown grasses have established.

Class 2: Plant germination is slower in Class 2 than Class 1. There are fewer weeds that compete with the pasture, and these emerge slowly. Legume growth is poor, so tall wheatgrass is more dependent on applied nitrogen to maintain vigour.

Class 3: These are often primary saline sites (i.e. saline prior to European settlement), and inappropriate to sow with tall wheatgrass-based pastures. Cultivation should be avoided. Separate fencing followed by deferment of grazing from December to mid-January will encourage the existing summer-growing species such as salt couch.

Fertiliser management

Pastures established on saline sites require adequate nutrition, either from the soil or from fertiliser, to achieve satisfactory production rates. Appropriate care is essential when applying fertilizer in wetter areas of the landscape to avoid pollution of waterways.

Phosphorus: Productive tall wheatgrass-based pasture requires soil phosphorus levels of 12–15 mg P/ha (Olsen P). If levels are lower than this, a phosphorus (P) fertiliser application will be necessary.

Potassium: During wet years, potassium (K) leaches out of saline soils. Fertiliser applications of 10-20 kg K/ha may be required after years of high water movement. Regular soil testing will enable objective assessment of potassium levels, as well as other soil nutrients.

Nitrogen: Tall wheatgrass often responds well to applied nitrogen (N), particularly on Class 2 land where legume growth is poor. Nitrogen levels can be raised with applications of 100 kg/ha of MAP or DAP in the year of sowing. Moderate to high levels of salinity restrict subsequent legume growth, and good responses can be expected from 50 kg N/ha as urea in late autumn or early spring.

Sulphur: Discharge areas are nearly always high in available sulphur (S). High-analysis fertiliser such as MAP, DAP and TSP (which are low in sulphur content) can be used in saline areas.

Grazing management

During the first growing season of a tall wheatgrass pasture, grazing should be light until November, to ensure plants are well anchored. After this, the pasture should be grazed when it reaches a height of 15cm, and grazed down to 3cm. Rotational grazing, a small paddock size, and large mob sizes are necessary to maintain the pasture in a vegetative state. Small areas should be fenced and managed separately to avoid under or overgrazing.

Control of spiny rush

Spiny rush is an introduced weed that grows on Class 1 and Class 2 saline land, and is not readily eaten by livestock. It can dominate saline and waterlogged areas, reducing its carrying capacity.  Landowners are required to take reasonable steps to control it and prevent its spread.

Control can be mechanical (mouldboard ploughing or mulching) or using herbicides. Control programs need to last two years to deplete the soil seed reserves, followed by planting of a vigorous salt-tolerant pasture to act as a strong competitor to any remaining seedlings.

Spiny rush
Spiny rush

Mulcher used for spiny rush control
Mulcher used for spiny rush control

Spiny rush after mulching
Spiny rush after mulching

Drainage

Drainage of surface runoff reduces the stresses of flooding and waterlogging on plants, while also improving animal welfare by creating drier areas for them to stand and camp.  Construction of drains that discharge surface runoff directly into waterways require the permission of the local Catchment Management Authority. However, minor earthworks that discharge onto one’s own property are permitted.

Interceptor drains divert surface water coming from higher up the slope.

Raised beds allow plants such as tall wheatgrass with less flooding and waterlogging tolerance to perform well on the beds, while the drains favour puccinellia. Raised beds also allow greater flushing of salts from the topsoil. The beds limit vehicle access, but allow livestock to avoid flooding during winter.

Ploughlands can be made by opposing passes of a one-way disc plough, followed by cross-harrowing. These are more easily trafficable than raised beds, but are not as effective as beds in waterlogging control or salt flushing. Care needs to be taken that not all the topsoil is removed from the drain areas, otherwise achieving pasture cover will be difficult.

Note: Drainage should not be contemplated on Class 3 salinity unless the surface is already bare, because of difficulties in restoring vegetative cover after earthworks.

Regional Information

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