16. david whitehead wet living lake nov17 · benefit to new zealand ... sam carrick tim clough...
TRANSCRIPT
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Reducing nitrogen losses from farms
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David Whitehead and colleagues
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New practical options are available to farmers to reduce nitrogen losses draining into groundwater and from gaseous emissions beyond current best practices by integrating fodder crops to manage carbon inputs to the soil
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Balmoral stony soilsCoarse fraction (> 2 mm)0.2 m depth 30–50%> 0.5 m depth 60–70%
Ashley Dene Research & Development Station
Reducing nitrogen losses from farms
National issue• Widespread conversion to intensive farming practices• Sensitive soils prone to nitrogen leaching, new regulations• Reducing agricultural greenhouse gas emissions• Solutions to manage tensions between increasing productivity, minimising
environmental impact, and exercising kaitiakitanga
Benefit to New Zealand• Hurunui: best practice could result in 17% decrease in nitrogen losses, allow
extra 6 680 ha conversion, increase value from milk exports up to $56 million/year
• Improve by additional 10% across Canterbury would allow headroom for 10 470 ha equivalent, with increase in value from milk exports up to $122 million/year
• Environmental, social, enhanced kaitiakitanga benefits
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Hypotheses• cycling of carbon and nitrogen in stony pastoral soils regulated by carbon inputs• nitrogen losses coupled to nitrogen immobilisation and denitrification • manipulation of carbon inputs will increase immobilisation and denitrification and decreases nitrogen losses
nitrogen leaching
soil microbial processescarbon cycling
immobilisation, denitrification
nitrous oxide emissions
carbon inputs• biomass• litter decomposition• root exudates• urine composition• dung
nitrogen inputs• fertiliser• urine• dung
Manipulating carbon inputs• crop type: ryegrass/clover ― lucerne ― kale ― fodder beet ― plantain• rate of biomass production: irrigation• urine composition
Molecular techniques• identify functional diversity• couple with biological drivers regulating leaching and gaseous losses
Leaching losses of nitrogen and carbon
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No Carbon input Sucrose rate 1 (12 t/ha)
Nitrogen le
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Carbon application rate
NH4‐N
NO3‐N
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Carbon input reduced nitrogen leaching by 41% under lucerne
No carbon input Carbon input 12 Mg/ha
Lucerne
William Talbot
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FB RG/WC FB RG/WC
Nitrogen leached (kg N/ha)
Urine
NH4‐N
NO3‐N
Mineral N
FB soil/crop RG/WC soil/crop
Nitrogen losses greater under fodder beet soil than under ryegrass/clover For fodder beet soil, fodder beet urine leached 16.6% less nitrogen than with ryegrass/clover urineFor ryegrass/clover soil, fodder beet urine leached 49.2% less nitrogen than with ryegrass/clover urine
Fodder beet – ryegrass/clover
Fodder beet soil Ryegrass/clover soil
Fodder beet Ryegrass/clover Fodder beet Ryegrass/clover
William Talbot
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Paddock scale carbon, nitrogen, water inputs and losses
irrigated lucerne
dryland lucerne
lysimeters
paddock scale sites
0 200 m
Startirrigated
2017
Startdryland
Startlysimeters
Cumulative net carbon balance 2 years
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Dai
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a-1IrrigatedDryland
Effluent irrigationRainfall
11290
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354294
47690
6 Apr 6 May 6 Jun 6 Jul 6 Aug 6 Sep 6 Oct
What’s going on below ground?
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• Conversion from dryland to intensive irrigated dairy farming is widespread on shallow, stony soils
• Leaching losses are unlikely in summer. Winter leaching losses respond rapidly to major rainfall events
• Nitrogen leaching losses from lucerne are attributed mainly to effluent applications
• Leaching losses can be reduced by manipulation of crop types and carbon inputs
• Investigation of microbiological processes will identify improved management practices
With thanks to our collaboratorsGwen Grelet Keith Cameron Brendon MalcolmJohn Hunt Hong Di Jo SharpPaul Mudge Grant EdwardsJonathan Nuñez William Talbot Steve WakelinJohannes Laubach Nik LehtoGraeme Rogers Hirini MatungaSam Carrick Tim CloughAndré Eger Yuan LiScott GrahamCarina DavisEva WeberRowan BuxtonJohn Payne