economics of underground drainage david armstrong ak consultants 23 july 2010
TRANSCRIPT
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Economics of Underground Drainage
David Armstrong
AK Consultants
23 July 2010
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Background
Focus today is on underground drainage rather than surface drainage
Assessment based on 3 examples Bishopsbourne, Hagley & Westwood.
Analysis assumes “strategic” rather than “comprehensive” drainage
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Strategic drainage Underground drains to low areas
With “feeders” to wet spots
NOT a grid or regular network of u/g drains
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“Brookdene”, Bishopsbourne
Under-ground drains since 1989
Mostly strategic; some paddocks almost comprehensive
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Costs & returns In 1989, $300-$350/acre over the whole
paddock.= $540-$630 in 2010 dollars ($1,300-$1,600/ha)
Oak paddock, drained 1998/996 ha, cost $6,000; $1,000/ha ($400/acre).
No drainage, 1,500 kg/ha peasWith drainage, 5,000; @ $0.34/kg (1998/99).
Benefit was worth $7,140 in total
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Costs & returns Oak paddock, potatoes a few years later.
Most harvested in October after a wet autumn
Yield averaged 20 t/acre, value $160/t after harvest costs.
Without drainage the potatoes would have rotted.
Benefit was worth around $40,000
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Costs & returns Bush paddock
Area of 12 hectares drained @ $400/acre (total cost $12,000).
Potatoes grown – yielded 24 t/acre.Impossible without the drainage.
With drainage Stewart has watered potatoes to soften the ground before harvesting
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Costs & returns Car Park paddock
Has had several potato crops
Poppies sown last year (2009)
Yielded 2.4 t/hectare.
Without drainage no potatoes, and poppies would have failed completely last year.
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“Brookdene” Without drainage
10% yield loss over the entire paddock.1 year in 10, complete crop loss.2 years in 10, 50% yield loss on 25% of paddock Average at 23% yield loss every year.
Rotation now Poppies, then rye grass for fodder Peas, then grass for 18 months Grass grazed for 18 months
Total Gross is $11,500/ha over 3 years.23% = $2,650/ha; drainage @ $1,000/ha
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“Brookdene” – other benefits Sure to get a crop, 90% of budgeted yield Sow on time Crop all of each paddock Spray when needed Good for soil structure Pugging, wheel ruts & compaction reduced
Disadvantage – paddocks dry quickly
Minimal maintenance requirements
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“Mill Farm”, Hagley DPI experiments in 1988-91
Comprehensive systems; 15 m spacings, 40 m spacings plus moles at 2 metres.
Cost was about $1,500/ha – on these results marginal. But showed that drainage works!
No Drains 15m Comp 40m + moles
Barley (2 years) 3.3 t/ha 5.9 t/ha 6.1 t/ha
Poppies (1 year) $2,009/ha $2,384 $2,788
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“Mill Farm”, Hagley Since 1992, 220 ha drained with strategic drains
Average 60 metres/hectare. At $9/m; $540/ha.
Mainly Cressy Association soil types: Clay loam over clay with gravel layers.
Grow a range of irrigated crops; poppies, cereals, onions and grass; plan poppies each 4th year.
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“Mill Farm”, Hagley
Without drainage – poppies risky
With other crops, average 20% yield benefit.
A 20% yield benefit with poppies and onions pays for drainage in 1 crop.
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“Highbrae” & “Oakleigh” Strategic drainage.
Generally Cressy Association soils.
7 paddocks drained, average 110m drain/hectare.
Cost around $1,000/ha
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“Highbrae” & “Oakleigh” East Bush paddock drained 2008. Poppies 2008/09; otherwise risky. Gross from poppies, $5,000/ha. Costs recovered with 1 poppy crop.
Gravel Pit paddock. Drained 2008. Grew seed potatoes 08/09. Potatoes impossible without drainage.
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“Highbrae” & “Oakleigh” Drainage allows planting of 20% of each
paddock that would be too wet.
Crop rotations 2 poppy crops in 4 years, with peas & grass. Then 3-5 years pasture.
Drained paddock – 20% higher lamb marking percentage last spring.
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Economics summary Economics depends on whether the drains
work!
On these 3 farms strategic drains work: Cressy & Kinburn Association soils Gravel layers drain well.
Strategic drainage, cost around $1,000/ha
Benefits, vary from year to year; General view average 20% extra yield
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Economics summary Irrigated crops;
poppies, potatoes, onions
20% extra yield covers cost in 1 year
Slower payback with lower value crops
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Other issues Drainage of agricultural land is a Landcare
operation – costs fully tax deductible in year of expenditure.
Drainage of swamps is NOT a Landcare operation, so not eligible.
Discharge of drainage water could reduce the quality of surface water and breach EMPCA.
It is likely to be subject to greater scrutiny in future.
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Conclusions
1. Sites like these case studies – underground drainage has been a very profitable investment; costs recovered in 1-2 years.
2. Depends on soil type; will it drain? Cressy & Kinburn soil types will drain (gravel layers help).
3. Generally restricted to land used for irrigated crops.