SA05SEQ-01: Management of Erosion & Sedimentation

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Research Site/Demonstration Number: SA05SEQ-01

Grower Collaborator: Piñata Farms – Wamuran

Location 1: Pates Road, Wamuran

Start date: February 2019


OUTLINE: To evaluate the benefits of surface stabilisation practices on low to moderate slopes to reduce/mitigate surface erosion and off farm deposition.


OBJECTIVES:

  1. To improve the methodologies of implementing surface stabilisation practices to better manage soil erosion.
    • Phase 1 – living surface covers (living mulch)
    • Phase 2 – synthetic surface covers (geo polymers)
  2. To understand the impact of mechanically controlled/isolated compaction or combinations with surface stabilisers.
  3. To reduce in-field soil erosion in highly erodible soil types.
  4. To undertake a cost analysis of implementing soil erosion practices.

METHODOLOGY:

The trial site has followed a previous crop of 73-50 hybrid which was only taken to plant crop due to poor health.  The previous crop harvested below industry standards in Spring 2018 with major issues of Phytophthora root rot, nematode, black beetle/white grub and natural flowering.  

The soil was prepared to standard industry conditions with good soil tilth, no crop residue and good soil moisture with a soil pH of 4.3.  The average slopes of the block are 2 – 3%. The block was established with industry standard herbicide practices which included a pre-plant incorporation and post plant drench immediately after planting.

Phase 1: Trial map – Pates Road Wamuran
(the yellow lines indicate the position of the contour banks)

Trial location prior to contour draining/soil opened up with plough to assist drying out.

Phase 1 – Two different living mulch species were planted, rye grass and oats 6 weeks after planting.  Planting of the living mulch involved an initial tillage operation with a tine into the inter-row to a depth of 10cm to open a furrow.  Seed was then planted by hand. A second tillage operation with the tine and then a final pass compressing the inter-row with the tractor tyres. The treated rows were 100m in length.

Opening the planting furrow

Seeding the inter-row space and burying seed/controlled compaction


DEMONSTRATION PRACTICE:

TREATMENT 1

Phase 1

Living mulch treatments:

  1. 25kg oats
  2. 25kg rye grass

Combined with controlled mechanical compaction with narrowed tractor tyres.

TREATMENT 2

Standard Practices – no ground cover


ASSESSMENT / EVALUATION METHOD & DELIVERY SCHEDULE:

  • Soil erosion (t/ha) – edge of field: Quarterly over 0 to 42 months
  • Cost analysis ($/ha): 42 months

PROGRESS REPORT

CURRENT PROGRESS:

February 2019
Grower identified
Site selected
Trial planned

March 2019
Block cultivated
Pre-plant pesticide and nutrition applied

April 2019
Bed-formed
Site planted
Treatments planted

July 2019
Erosion assessed.

ISSUES ENCOUNTERED: Constant rainfall disrupting land preparation during establishment of block.  The site has subsequently been relatively dry for the majority of the trial period.

OTHER NOTES: The site also supports a fumigation trial.


RESULTS

Phase 1 – Soil stabilisation with living mulch

The initial results have indicated that living mulch can be planted with moderate success into pineapple fields that have been treated with industry standard herbicide programs.  Both rye grass and oats was able to establish into a soil with herbicide residue present. However, growth was limited to 10 – 15cm before the living mulch died. This also coincided with the first rainfall event of 20mm.

The vegetative mass/cover of both living mulch crops was able to stabilise the soil to a moderate degree.  In this case, the oats were more successful than the rye grass.  

The addition of mechanically controlled compaction (tractor tyres) in the inter-row further assisted the living mulch seed to establish but also supported stabilisation within the highly erodible areas of the furrow.  

Prior to the first sampling the site received 20mm rainfall over a four-hour period. 

Soil Stabilisation – Living Mulch (2 weeks after planting)

Rye grass (left), oats (right)

After 20mm rainfall: high erosion where there was no ground cover (left), low erosion in the presence of living mulch (right)

The amount of soil eroded from each treatment was measured by laying 10m lengths of plastic at the ends of the rows that was wide enough to collect the eroded soil. 10m was enough to collect all the soil that washed out of the ends of the interows and after the rain event the soil on the plastic was collected and weighed.

Treatment Amount of Soil Eroded (kg)
Rye grass 6.4
Oats 5.5
Nil 16.0

Note: Sampled July 2019 – total rainfall at that time 20mm

After 4 months the living mulch has died from the effects of the standard herbicide treatment

Even after the living mulch had died, the vegetative matter remains and continues to stabilise the inter-row minimising erosion.  However, the vegetative matter within the rye grass area was minimal. Soil erosion measured in the rye grass area was marginally more than the well-established oats.  The controlled compaction in both treatments has most likely had a major impact on the soil erosion. 

This trial is ongoing.