Masterton District Council’s (MDC) eight-year Review of Homebush WWTP operation is the apparent origin of the $12.2M “Beyond Homebush” plan to pump water to nearby private landowners. Significantly, the review does not critically examine irrigation practices, or consider alternative crops. Short rotation crop (SRC) willow would grow exceptionally well in the Homebush soils under a properly-planned irrigation strategy. Conservatively, the site can produce 16 Oven-Dry-Tonne (ODT) biomass from established plantations, per hectare, per annum, easily meeting MDC’s goal: Land disposal will be maximised so that discharge to the river and associated effects on its mauri and amenity values can be minimised. (Upgrade Summary Report, May 2007.)

There are other advantages of a SRC willow system over a pasture-based one including:

  • Pasture irrigation is on a seven to ten-day cycle depending on soil moisture conditions. SRC willow can increase the cycling rate due to its superior water-use.
  • SRC willow plantations have a life expectancy of 15 to 20 years. Currently, pasture is renewed every four years, so each season, 25% of the area cannot be irrigated until the crop becomes established.
  • Land discharge condition 22e, requires soils to dry out so that harvesting machinery can operate without causing wheel ruts. There are up to four pasture harvests per year, each requiring abstinence of irrigation under the pasture system.
  • Further delays follow while the crop is mown, windrowed, baled and carted away, potentially losing another month to the grass irrigation season.
  • SRC willow plantations could be irrigated for a seven month period from when they come into leaf in early September through to the on-set of leaf yellowing in late April.

Establishing and managing a SRC willow system is nothing new; having been employed in the Northern Hemisphere for many years, mainly to supply fuelwood for local power stations, so the knowledge and technology required is easily sourced.

SRC provides potential for a circular economy through displacement of coal by willow fuelwood. Combustion of air-dried willow billets is deemed carbon-neutral, with the CO2 released being equivalent to that sequestered.

Through photosynthesis SRC willow directly captures CO2 from the atmosphere. Overseas research shows that, over a three-year rotation, a SRC willow plantation could conservatively sequester over 57.2 tonnes of CO2 per hectare of total biomass.

Converting this biomass to biochar can positively impact MDC’s climate-change goals. The International Panel on Climate Change (IPCC) has designated pyrolysis biochar a credible negative emissions technology (NET) with potential for large-scale removal of CO2 from the atmosphere. When incorporated in soil, biochar becomes a carbon sink, lasting thousands of years. This should be of particular interest to the NZ Government.

Achieving financial viability for a biochar industry is very much in the government's hands and revision of the Emissions Trading Scheme (ETS). To achieve a sustainable biochar industry in New Zealand we need:

  • Government recognition of biochar’s value
  • the formation and oversight of market(s) for sequestration credits
  • end-to-end quality control and certification
  • strategic funding of pilot demonstration projects
  • information and extension services that share results from pilot projects, and allow biochar production and application to be continuously refined.

Homebush could play a pivotal role in piloting the development of a biochar industry, including demonstrating the SRC willow wastewater system and the interim use of the biomass for fuelwood. The value is to MDC and the Masterton community, to the other Wairarapa councils, as a blueprint for their own wastewater upgrades, and ultimately, the benefits could be nation-wide.

  1. Masterton District Council Wastewater Effluent Disposal Eight Year Review; October 2022.
  2. Condition 22g) No treated wastewater shall be discharged to land where pasture, or a crop, has less than 4 weeks of growth after being replanted or sown, except in dry weather conditions where the pasture or crop is under stress.

Later news entry: Take the Jump Wairarapa supports “Why Electrify Wairarapa?”

Older news entry: GWRC support work at Uriti Point