Week 4

• Pesticides


  Chemicals used to control weeds, plants and insect pests
• Pesticides


  • Used in the agricultural sector
  • Legacy contamination from historic use
• Types of pesticides


  • Insecticides
  • Fungicides
  • Herbicides
• Food safety risk - Trace amount of pesticides must be monitored
• Reasons for using pesticides

  • Boost agricultural yields
  • Prevent loss of crop yields due to plant diseases, insect and bird predation, and weed competition
  • Address post-harvest issues due to rodents and fungi
  • Biosecurity/protect biodiversity
  • Control insect-borne diseases
• Less than 10% of pesticides reach the target organism
• Environmental impact of pesticides

  • Accumulate in soil
  • Runoff can enter ground and surface water
  • Can be transported long distances in the atmosphere
• Half-life


  The time it takes for half the original amount of a substance to disappear
• Accumulation in food chains is a significant concern, bioaccumulation factor (BAF) is a measure of accumulation for a contaminant in an organism
• Adverse effects of pesticides

  • Water contamination
  • Effects on non-target species
  • Human health effects
  • Impact on soil function and nutrient processing
• DDT


  Persistent organochlorine pesticide used in 1950s and 60s, banned in 1989
• DDT degrades and forms DDE and DDD which have very long half-lives, management continues today, over 80 years on
• 1080


  Controversial vertebrate poison, effective in killing possums but has a range of by-kill such as birds, reptiles, frogs, fish, insects, dogs, deer, pigs
• 1080 breaks down in the environment quickly, and is effective in killing possums to stop the spread of bovine tuberculosis
• Pesticide alternatives


  • Change usage, only when necessary
  • Mulches to control weeds
  • Encouraging beneficial insects
  • Switch from monoculture to polyculture
  • Pheromone pest control methods
  • Biological control-introduction of pathogens to reduce pests
• Integrated pest management


  Bringing all the alternatives together, has reduced the use of insecticides by 80%
• Another significant legacy issue is the use of extremely toxic DDT and arsenic, which continues to raise concerns for NZ trading of meat products today
• Soils are a non-renewable resource, once it is damaged or contaminated there are limited options for revival
• Only 5% of land in New Zealand is classified as high class, flat and suitable for growing fruit and veges
• Key threats to soil

  • Erosion
  • Flooding
  • Urbanisation
  • Depletion of nutrients for animal and plant growth
• Key pressures on soil

  • Intensification (particularly irrigation, addition of more chemicals, inadequate vegetation cover)
  • Land use change (rising trends of urban expansion)
  • Legacy (mostly impact of past deforestation, pests and diseases)
• How soil is impacted

  1. Compaction (soil is compressed which reduces the air pockets between soil particles)

  2. Pugging (stock trampling on wet soil- changes the structure of the soil by breaking down soil aggregates)

  3. Erosion (natural process being accelerated by human activity)
• Compaction occurs from heavy machinery and livestock, as well as effluents and nitrogen puddles from cows
• Pugging takes years for soil to recover, causes poor drainage, and susceptibility to further pugging
• Pugging causes more topsoil and contaminant run off (such as DDT and phosphorus) into waterways and soils
• Erosion is accelerated by vegetation removal, and New Zealand is erosion prone due to high rainfall, steep terrain, unstable rock, and large areas of land cleared/overgrazing
• Erosion impacts light and photosynthesis, habitat loss and smothering of organisms by mud
• Urban expansion and creation of lifestyle blocks reduces available land for horticulture, with 10% of high-class land in lifestyle blocks
• Soils are depleted, affecting crop and animal health
• Soil contamination sources


  • Legacy issues like DDT and sheep dips
  • Fertilisers
  • Pesticides
  • Irrigation waters
  • Re-use of waste products
• Soil contamination impacts animal and crop health, soil function, nutrient cycling and changes the structure
• Cadmium is a key contaminant in phosphate-based fertilisers and is readily taken up by plants from acidic soil, bioaccumulating in leafy vegetables
• DCD (applied to farms to prevent leaching of nitrate) was found in milk products
• Overall soil depletion effects crop and animal health and eventually us as contamination goes through the food chain
• There are very limited remediation options once contaminant concentrations reach unacceptable levels
• Sustainable approaches


  • Increase diversity (rotate crops, larger variety)
  • Crop that would stabilise soil and nutrients
  • Insect pheromones
  • Agro forestry
  • Reducing uses of chemicals and pesticides
  • Use of mulches to control weeds
  • Encouraging use of beneficial insects
  • Switch from monoculture to poly culture
  • Biological control – pathogens
  • Restoration of wetlands, riparian planting (can also capture nitrogen)
• Utilising farm waste and compostables

  To increase soil biodiversity and help limit the extraction of key nutrients (phosphorus and nitrogen)
• Using ryegrass and clover

  To help fix nitrogen - can be used in dairy farming also reducing the need for nitrogen fertilisers
• Agroforestry


  • Combines forestry and grazing animals to best make use of the space
  • Fodder crops to feed grazing animals
  • Timber
  • Nuts and fruit
• Benefits of agroforestry


  • Helps with erosion control
  • Rich habitat for birds and insects-enhances biodiversity
  • Helps with carbon sequestration
  • Is profitable