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The FFC – Information – Weed Management – Intrarow Soil Thermal Weeding (ISTW)

The FFC’s work on thermal weeding including intrarow soil thermal weeding has been featured on TV1’s Rural Delivery program.

This research was funded by the Sustainable Farming Fund, project number L12-104.

1. Expanding the Potential of Intrarow Soil Thermal Weeding. May 2013. Report number 4-2013 Version 2. Jump to Executive Summary

2. Intrarow Soil Thermal Weeding Supplemental Report:An Analysis of the Potential for Ex-field Heat Treatment. July 2013. Report number 6-2013

3. Intrarow Soil Thermal Weeding Supplemental: Final In-Field Design for Low Energy Consumption and High work rates – version 2. August 2016. Report number 2-2016

4. Soil thermal weeding. University of Canterbury, Dept. of Mechanical Engineering, Final Year Project, and higher temperature & duration seed treatment. August 2019. Report number 01-2019

Expanding the Potential of Intrarow Soil Thermal Weeding – Executive Sumary

  • Globally, herbicide based weed management is facing the triple threats of herbicide resistance, dwindling discovery and legislative prohibition, to the point that leading weed scientists are proposing a post-herbicide era.
  • It is therefore vital that non-chemical (non-herbicide) weed management techniques are rapidly expanded.
  • Intrarow soil thermal weeding (ISTW) is potentially unique among non-chemical weeding tools, in that it is a direct replacement for herbicides and it can outperform herbicides efficacy.
  • ISTW works by killing the emergable weed seedbank in the intrarow, thereby completely eliminating therophyte weeds from the crop row, for the entire length of the crop production cycle. As it is applied prior to crop establishment, it works with any (row)crop.
  • However, current ISTW machine designs use steam as the heat transfer media, which considerably increases the mechanical complexity, size, cost, etc., of the technology, and they use large quantities of fossil fuels.
  • This report analyses the current ISTW technologies, and proposes using hot air as the transfer medium to address the mechanical complexity issue, and more critically, to allow recycling of the heat in the treated soil so potentially significantly reducing energy / fuel use.
  • It also analyses the potential to use renewable fuels to replace fossil fuels, showing that vegetable oil and biogas (methane) are mechanically simple to substitute for diesel and natural gas (respectively) and as these are also among the most common farm produced biofuels their uptake is not inhibited by supply issues, although cost is still a factor.
  • The synthetic literature review section identifies a number of key parameters / variables affecting the efficacy of ISTW, which are:
  • Soil and seed moisture;
  • Soil aggregate size;
  • Temperature.
  • Experiments were therefore undertaken to further study these effects. These found that:
  • Moisture has multiple interactions including higher moisture increasing seed death, increasing the energy required to heat soil and, for silt and clay soils, facilitating a loss of soil structure, potentially leading to severe compaction.
  • Increasing soil aggregate size resulted in decreased weed seed kill;
  • Temperature alone is not a good predictor of seed death and that thermal time (treatment temperature × heating duration) is likely to be a better predictor.
  • The research also found that hot air was an effective medium to heat soil, however, weed seed mortality was lower than for steam, possibly due to the lower moisture levels of hot air, but also possibly due to other unknown factors.
  • The outcome of this report is to provide a theoretical underpinning for the construction of prototype hot air recycling ISTW machinery with the ultimate aim of agricultural machinery manufactures producing farm-ready machines for farmers and growers to use.
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