Trial Code 3.4: In-furrow erosion minimisation

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Start Date: 4/5 December 2019

For more information:
Rachel Abel
Department of Agriculture and Fisheries
07 5381 1322
0436 637 570
Rachel.Abel@daf.qld.gov.au


SUMMARY

Of the nine treatments tested at this site, three whole plants and the hydromulch treatments are the most promising to reduce erosion in comparison to the standard practice at the farm. I am keen to investigate one or both of these options further with interested growers in South East Queensland.

TABLE OF CONTENTS


TRIAL INFORMATION

The trial site is located in South East Queensland. Row length is approximately 100 metres on a 3.1% – 3.9% slope. The treatments are as follows:

  1. Control – No Treatment
  2. 4 Pines in a diamond pattern
  3. 5 Pines in a row across the furrow
  4. 5 Pines in a row across the furrow with a whole plant above
  5. 5 Pines in a row across the furrow with living mulch
  6. 3 Whole plants
  7. Living Mulch
  8. Polymer – Stonewall
  9. Hydromulch – coarse sugar cane mulch with polymer glue


Figure 1 (above) shows the layout of the trial on the farm. Each replicate had one furrow dedicated to each of the 9 treatments, giving 4 furrows of each treatment in total applied randomly across the block to account for unseen variability. The treatment order is shown in Table 1.

Five of the treatments had pineapple plants placed in the furrow to act as barriers to slow water flow and reduce erosion. There were two types of barriers used in the trial. These were tops which were in good condition or whole pineapple plants which would have alternatively been incorporated back into the soil. The barriers occurred for the following treatments: five pines, five pines + plant, three whole plants, five pines + living mulch and the diamond pattern. The spacing for the locations of each barrier within a treatment is shown in Table 2. Replicates 3 and 4 increased the number of barrier sites to account for increased slope and length. The hydromulch, stonewall and both living mulch treatments were applied along the full length of the furrow.


WEATHER CONDITIONS

The trial was planted on the 4-5 of December 2019 in hot conditions into dry soil. The first rainfall post planting was in mid-January and by 10 March 2020 totaled 745 mm. The total rainfall received (953 mm 4/12/2019 – 20/4/2020) is shown in Figure 1. Measurement dates indicate when sediment traps were emptied and erosion data recorded.


PHOTOS

Photos dated 22 January 2020: The photo pairs below show the top and bottom of the same row for one of the replicates. In total there are 4 replicates.

Control – No Treatment

4 Pines in a diamond pattern

5 Pines in a row across the furrow

5 Pines in a row across the furrow with a whole plant above

5 Pines in a row across the furrow with living mulch

3 Whole plants

Living Mulch

Polymer – Stonewall

Hydromulch – coarse sugar cane mulch with polymer glue


DETAILED RESULTS

Table 4 relates to the soil captured in sediment traps up to the 10 March 2020. There amount of sediment actually measured in each column is presented. However, given the rainfall and the amount of soil movement some sediment traps overflowed and in some cases the the trial layout has impacted on sediment trap amounts so these corrections are reflected in the estimated sediment amount. The estimated sediment is an assessment of what may have occurred if the challenges outlined in the comments section did not arise.

The hydromulch and whole plant treatment have very high efficacy in reducing erosion losses. How these treatments are performing is exceptional for erosion control when compared to conventional practice. However, it is important to remember that we are currently 5 months into a 20-22 month trial. Both of these treatments are plant material based and it is likely that the plant material will breakdown prior to the trial ending. Historically, erosion trials that have included similar treatments demonstrated that losses reduce over time. This is likely due to the beds being “settled” and the soil has protection from rain droplet impact due to increased leaf coverage. Monitoring is ongoing with this trial.

I would encourage growers to be curious and have a go at one or both of these erosion control options on a small scale. There is enough evidence to have a look at either one of these treatments with cautious optimism. I would like to work with growers to further evaluate the control measures as options for industry and monitor any unintended impacts of the treatment

Control – No Treatment

5 Pines in a row across the furrow

5 Pines in a row across the furrow with a whole plant above

3 Whole plants

Hydromulch – coarse sugar cane mulch with polymer glue

 


FINANCIAL COSTS DISCUSSION

Control – No Treatment

Measured loss of 50.6 T/ha, estimated loss exceeds 100 T/ha.

Nil financial outlay

5 Pines in a row across the furrow

Measured loss of 48.3 T/ha, estimated loss of 85 T/ha.

Cost of treatment

Comments

  • There is an intention to measure these plants to see if they yield marketable pineapples to offset the costs of establishment.
  • One replicate was discontinued for measurement due to the complete failure of the establishment in one row. See Figure 3 for more detail.
  • Treatment often caused rill or bed erosion due to the changed water flow characteristics as seen in photos below.

This treatment is not recommended at this site from the current data collected.


Bed erosion


Rill erosion

5 Pines in a row across the furrow with a whole plant above

Measured loss of 35.5 T/ha, estimated loss of 50 T/ha

Cost of treatment

Comments

  • There is an intention to measure these plants to see if they yield marketable pineapples to offset the costs of establishment.
  • Treatment regularly caused rill or bed erosion due to the changed water flow characteristics see photos below and Figure 3 for more detailed assessment.

This treatment is not recommended at this site from the current data collected.


Effective 5 Pine + Plant barrier


Not effective 5 Pine + Plant Barrier

Three whole plants (previously harvested, would have normally been incorporated as pine trash. Placed roots upslope, leaves downslope)

Measured loss 9.9 T/ha, estimated loss 3 T/ha and adjusting the layout by moving the barriers closer to the sediment traps would reduce estimated losses further.

Comments

  • There is an intention to measure these plants to see if they yield marketable pineapples to offset the costs of establishment.
  • Treatment rarely caused rill or bed erosion due to the changed water flow characteristics see photos below and Figure 3 for further details.
  • One furrow on a change of soil type for a portion of the row was more susceptible to rill and bed erosion. This indicates that the treatment may have a different effect on different soil types and will need further site specific investigations prior to BMP recommendation.
  • Does create a dam like effect of sediment within the furrow. There is a concern that it may impact the plants with reduced drainage from the dammed sediment in the furrow being at the height of the bed. Monitoring plant health through drone imagery and yield data will be conducted.
  • Due to the potential build up of sediment at the top of the row, run-off from further upslope may divert into laneways. Maintaining laneways for drainage and erosion minimisation will be important in conjunction with this treatment.
  • Using pineapple trash as mulch was tested back in the 80’s and 90’s by Cyril Cieszolka. He found that pineapple trash used as a mulch is durable and effective at reducing soil erosion.

This treatment has a lot of potential as an erosion control option. Soil types, plant placement and slope will be important to gather further information regarding to improve understanding of best practice.


Effective Whole Plant barrier


Slight rill erosion whole plant barrier

Hydromulch – 100mm depth of coarse sugar cane mulch with polymer glue applied on surface of mulch

0 T/ha sediment captured, visually water outflow looks less turbid.

Comments

  • This can be done cheaper through production of own mulch and improved mechanism of applying mulch. Alternatively, using whole plants at 1.2 plants per linear meter for 7500 linear meters per hectare is 9,000 whole plants per hectare – scaling up from the previous costs approximately $2000. This may be excessive and there could be savings through economy of scale which bring that cost down further.
  • Sediment seemed to push out from the side of the bed into the row and be trapped by the mulch.
  • Heavy rainfall events did not cause the mulch to move. This is likely a combination of the glue, thickness of mulch and timing of heavy rainfall that the base of the mulch was already buried in sediment
  • Due to the potential build up of sediment at the top of the row, run-off from further upslope may divert into laneways. Maintaining laneways for drainage and erosion minimisation will be important in conjunction with this treatment.
  • The sugar cane mulch is visiablly degrading, it is unlikely to last until harvest in Septemter 2021.

Exceptional efficacy however costs and application practicalities mean this treatment is harder to implement in the short term.

Less tangible costs and benefits of less soil erosion

Benefits

  • No reintroduction of weed seeds into block when returning topsoil to fields
  • No costs associated with excavating, trucking and spreading returned topsoil to field
  • Top soil remains in field and actions to improve long term soil health may be more effective
  • Slowed water flow less erosive, potential improvements to headland traffic ability due to less rill erosion

  • Keeping soil in the paddock will reduce the quantity of pesticides and nutrients that enter the waterways
  • No desilting dams required
  • Increased flexibility in ground preparation when whole plants are harvested, may be immediately able to prepare block without time for plant breakdown
  • Increased flexibility for the collection of fresh large slips for replants

Costs

  • Introduction of weeds in soil attached to whole pines or mulch – can be mitigated by using ground suckers if viable for collection or careful selection of block to collect who plant material from.
  • Introduction of disease from soil attached to whole pines or mulch– can be mitigated by careful selection of block to collect whole plant material from
  • Post herbicide activity in the field potentially breaking the herbicide layer – didn’t appear to be an issue at this site however caution should be utilised.
  • Reduces volume of pine trash for incorporation which is is an important soil health measure. If undertaken on a broadscale blocks with whole plants removed may require adjusted management program.

Effectiveness of the pineapple plant barriers in furrow at holding sediment back without causing erosion.

We rated the efficacy of each of the sites of the five pines, five pines + plant and whole plants for their impact on erosion.

Rating Scale for effectiveness of each treatment

0 = Not Effective, sediment not trapped and/or eroded the bed
1 = Effective, held back sediment, but potentially a bit of rill erosion
2 = Effective, held back sediment, no sign of erosion

Whole plant treatment generally looked very good and rarely caused any significant erosion of the beds. Replicate 4 was an outlier and the poorer performing areas were in a different soil type which is present in the corner of that block. This may indicate that this treatment will have different effectiveness on different soil types and will need further investigation.

5 Pines was mostly showing some rill erosion and/or erosion of the beds.

5 Pine + Plant was an improvement on 5 Pines but not as good as the whole plants

Discontinued treatments

Four treatments were discontinued after early rainfall events. Early data indicated they were not as effective as the control. Measurement was abandoned due to the labour intensity of the data collection.

Living Mulch and 5 Pines in a row across the furrow with living mulch

The living mulch never established. Hot dry weather for 6 weeks post planting did not allow for germination. During this time, a large flock of ducks predated living mulch seed. Post rainfall, small numbers of living mulch germinated though the herbicide killed the seedlings.

Polymer – Stonewall

The Stonewall initially looked positive, however after several rainfall events the treatment began to erode. While it was not exceeding the mass in the control, the treatment was excluded from further measurement due to the cost with limited efficacy it was unlikely to be recommended as a viable option to industry.

However, it is important to understand why in this scenario the Stonewall did not perform as expected.

  • Soil moisture – weather conditions was hot (35°C) and light winds on the day. Very little soil moisture was present in the block. It was attempted to moisten the soil with a pre-spray, however due to the initial very dry soils and the weather conditions of the day the soil moisture may not have been adequate to provide suitable conditions for the product to form a barrier
  • Product placement – the trial aimed to minimise the cost by focussing the application on the sidewalls and furrow. Our application could have had a greater focus on the edge between the top of the bed and the sidewall. In hindsight, Stonewall is likely to perform at its most optimal with full coverage of the bed, sidewall and furrow.

Susie Chapman has a site adjacent to this block. She will be able to provide a better understanding about its performance on this soil type, which has over 20% gravel (particle size greater than 2mm).

4 Pines in a diamond pattern

At the first emptying of the sediment traps, this treatment contained more sediment than the control. Water seemed to create rill erosion as it moved through the diamond. Soil type may influence the efficacy of this treatment

 

Thank you for reading folks. Please contact me if you have any questions or comments.

Rachel Abel
Rachel.abel@daf.qld.gov.au
0436 637 570

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