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Sustainable soils and soil fertility

In a nutshell...
  • The soil is the basis of all farm productivity.
  • The soil is where you start planning your sustainability programme.
  • New Zealand has a wide range of soil types (more than 1000), and it's important to know what kind of soil you have.
  • NZ soils are formed from a diverse range of parent materials, ranging from old sedimentary rocks to recent volcanic ashes.  These vary greatly in texture and natural fertility.
  • Generally New Zealand soils are low in nitrogen (N), phosphorus (P), Potash (K) and Sulphur (S).
  • Good soil structure consists of aggregates ranging from crumb to nutty.  These must be maintained as they are the basis of air and water flow around plant roots.
  • This will also allow the bacteria in the root nodules of clovers to fix nitrogen from the air at no cost to the farmer.
  • A healthy soil also maintains a massive number of micro- and macro-organisms (bacteria, fungi, protozoa and earthworms).
How can you tell if you have a problem?
  • Poor pasture growth over the whole season.
  • This is most noticeable when the spring flush which does not occur.
  • Lush pasture growth around dung and urine patches which stand out clearly.
  • There is very little ryegrass present - the ideal is 70%.
  • There is very little clover present - the ideal is 30%.  What clover is there is weak.
  • The pasture is made up of poor plant species, most noticeable in summer.(See Pastures)
  • There is a very high incidence of weeds.  (See Weeds) 
  • Some farmers (See Organics) are not concerned about many of these weeds as stock eat them and they add variety to the diet.
  • There are large bare patches in the sward.
  • The pasture is being pulled up in clumps by the stock while grazing.
  • There are patches where the pasture is dead.  Likely to be insect damage. (See Insect pests)
  • The pastures "poach" or "pug" (form mud) easily when grazed during wet conditions.
  • Compacted layers form within 200mm of the soil surface.
  • Water ponds (forms puddles) on the surface after rain.
  • Pastures do not last and large parts of the farm have to be resown each autumn.
  • Leaching of nitrates into the ground water.
How can you tell if you're doing well?
  • A soil profile showing plant tap roots going down below 200mm.
  • The soil can be broken by hand into good crumb and nutty structure.
  • More than 2-3 earthworms for each spade spit.
  • Soil to smell pleasantly "earthy" and not sour.
  • A green leafy sward with good growth rates (DM/ha/day) all the year round.
  • Good spring flush with growth over 100kg DM/ha/day.
  • Healthy grass and clover in a 70/30 proportion.
  • No low productivity species.
  • No weeds and no areas of bare ground.
  • Dung and urine patches are not prominent and do not show for a long time.
  • No dead areas of pasture due to insect damage.
  • No pulling of pasture.
  • No pugging when wet.
  • No puddles during wet weather, or if there are they do not persist.
  • Pastures last for many years and no need for regular renovation.
What can you do to improve things?
  • Have regular farm walks to check pasture growth.
  • Be aware of the pasture growth pattern for your particular farm.
  • Regular soil test (2-3 years).
  • Carry out recommendations by fertiliser consultant to keep soil nutrients at optimal levels for your soil type and farming system.
  • There is no point in putting on more that is needed.
  • Don't forget lime.  It's not strictly a fertiliser but low pH will limit fertiliser utilisation.
  • When applying fertiliser, avoid runoff and loss of nutrients into the air.
  • Do not spread fertiliser right up to the edge of streams.
  • Keep a vigorous clover content (minimum of 30%) to exploit the free nitrogen from the air.  This can be the equivalent of around 230kg N/ha/year.
  • Plant new pasture species and appropriate cultivars for soil type and production potential.
  • Prevent pugging during wet weather by removing stock from pasture.
  • Aerate or subsoil paddocks (especially on dairy farms) to repair compacted layers.
  • Fence off waterways and prevent stock grazing up to the edge of waterways.
  • Develop riparian strips and wetlands to reduce chemical pollution of waterways and also to act as sediment traps
  • Do not let stock drink out of waterways.  Provide water in troughs.
  • Don't have day and night paddocks to prevent fertility transfer.
Where can you go for help?
  • Regional Councils
  • County Councils
  • Federated Farmers of NZ
  • Ministry of Agriculture and Forestry
  • Department of Conservation

Dr Richard Chapman, Soil Consultant.  Phone (07) 829-5437

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