Newletter Soils and Fertiliser - 17th May 2011

 Prepared By Ginny Dodunski


Ian McNab, AgKnowledge: ‘Back to the future' - Rational fertiliser use for your farm... 2

Overall ... 2

Nitrogen ... 2

Phosphorus ... 3

Common findings in dairy sector (and NI intensive finishing farms?) ... 4

Common findings in sheep & beef sector ... 4

What should you do?... 4

Caution ... 4

Dr Alec Mackay; AgResearch: Land development - What else is there? ... 5

Phosphate levels ... 5

Drainage ... 5

Farm LMU's (Land management units) ... 5

Benefits of lime ... 5

Humates ... 6

Soil compaction ... 6

Earthworms ... 7

Dr Alec Mackay; AgResearch: Can we actively improve the natural capital in our soils?   7

Overview of NZ soils ... 7

The future of land development?... 8

Dr Alec Mackay; AgResearch: Land development - What else is there?


Phosphate levels

What Olsen P SHOULD high- performing finishing farms be targeting?

Recent dairy example:

  • Average producing farms on sedimentary soils in supply area have Olsen P of 20-30
  • Top 25% of farms in same area have Olsen P of 30-40


  • Many intensive sheep and beef blocks still suffer from poor drainage; yet cost of drainage proportional to land value has never been cheaper
  • Return on investment within 3-5 years
  • This is driven by: better pasture production; efficiency of nutrient use; ability to change land use (cropping/increased stocking rates); better lamb survival in sheep breeding systems?

Farm LMU's (land management units)

  • Differential fert use/approach on flats, hills
  • Recognise limitation of traditional P&S/Legume approach on areas where clover is difficult to establish and maintain (e.g. dry north-facing slopes); these areas may produce more with an N-based approach

Benefits of lime

  • ‘Soil amendment' - improves pH, reduces availability (toxicity) of aluminium and manganese, improves availability of molybdenum (required by clover)
  • Appears to reduce hydrophobicity; AgResearch currently studying this phenomenon (where soil does not ‘wet up' easily):
    • potential gains from ameliorating hydrophobicity
    • developing a measure for it
    • developing solutions

BUT don't forget superphosphate contains 20% calcium, and soil Ca test will increase over time with increasing super applications


In soils void of significant quantities of clay minerals and organic matter (e.g. raw sands and podzols, intensively cropped horticultural soils), addition of humates can impact significantly on:

o   Soil fertility - improved plant growth

o   Soil structure

o   Biological activity

o   Water holding capacity

o   pH - buffers this

o   Planting root growth

Data on the efficacy of these is lacking for New Zealand pasture soils.

NZ Arable soils                     3.5% organic C,   6% OM

NZ Pasture soils                  4.9% organic C,   8.4% OM

Peat soils                              46.0% organic C, 79% OM

Cations/Base saturation

o   Cations are positively charged nutrient ions

o   They may be basic (Ca, Mg, K, Na) or acidic (Cl, H, Al)

‘Conventional' approach:

o   Ensure  plant-available nutrient levels (K and Mg) not deficient

o   Ca applied in lime and P fertilisers (20% Ca)

o   Some more recent advice advocates having cations balanced (e.g. Ca) according to specific ratios - linked to greater crop yield and nutritional quality

o   Data to support this is lacking

o   This approach may result in significant extra expense of inputs beyond requirements

Soil compaction

  • Increased weight of livestock/Ha as carrying capacities increase; increases risk of soil compaction once cattle become a dominant part of the system especially during wet parts of year
  • Treading damage and intensive cropping increase soil compaction which can result in:
    • Lower plant productivity (30% reduction in pasture production in season after compaction event has been consistently measured)
    • Reduce rooting depth, nutrient & water extraction
    • Increase in trace gas emissions (e.g. N2O)
    • Reduced surface infiltration, greater surface water run-off and losses
    • Reduction in efficiency of use of inputs (e.g. fertiliser?)
    • Loss of habitat and biota

Recent NZ work in dairy systems shows that compacted soils require a higher Olsen P to maintain the same level of production (or conversely that the reduced pasture production from compaction can be overcome to some extent by raising Olsen P


  • There was never a systematic release of earthworms in NZ; they were accidental introductions so distribution is patchy
  • 2-3 species in NZ; mostly surface dwellers and shallow burrowers
  • 171 species of native earthworms but these do not persist once bush is cleared
  • A 2009 survey of farmland in the BOP/Waikato region found 53% of sites did not have earthworms, and only 20% of sites had deep burrowers

The value of surface-active earthworms:

  • Reduce the turf mat
  • Improve incorporation of surface applied materials (e.g. lime)
  • Increase pasture production (10-30%)
  • Reduce infective L3 larvae

The value of deep-burrowing earthworms:

  • Improvements in air permeability and water infiltration
  • Increased pasture production (10-20%)?
  • Act as a substitute for the surface active earthworm species in intensive livestock systems as they can stand treading
  • These are absent from large areas of NZ: most of SI and most of NI East Coast

But to read more from Alex and all the other great information from the day pdf Newsletter Manawatu Finishing Farms AgResearch... (0.34MB) 
- if for some reason you can not open the file please email