This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Polyethylene film mulch was used on a commercial processing ‘Ranger Russett’ potato crops in North West Tasmania in the 2007/08 and 2008/09 seasons.

The aim of the project was to assess the impact of the film on potato plant growth and development; in particular to assess yield and tuber quality in early planted potato crops.

In the first trial (initiated September 2007), four weeks after planting, crop percentage emergence was significantly less in film treatments compared with the control. The film increased soil temperature such that the potato stems were burned or “solarised” as they emerged. This dramatic effect led to a re-thinking of both the usage timing and the thermal characteristics of the film. The trial in the second season therefore focused on earlier planting and films were investigated where light reflecting properties changed with film age.

In the second trial (initiated August 2008), emergence was earlier in the film treatments compared with the control, by about two weeks. This indicated that earlier crop emergence, particularly in early planted crops, could be achieved with use of film. Earlier emergence may have increased the length of the growing season, and potentially increased yields, in early harvested crops.

Tuber development began earlier under the film treatments compared with the control. In treatments where film remained after emergence, tuber development was more advanced compared with treatments where the film was removed at emergence. This indicated that the impact of the film on king tuber size was post emergence.

Results indicated that the use of film may alter yield structure, with fewer small potatoes (<75g) from under the film treatments. In some instances this may have increased the “processing yield” of potatoes.

Observations through the life of the crop indicated that there was better utilisation of existing water resources particularly through decreasing evaporative losses early in the life of the crop. In addition to this, under film, there was potentially an increase in usable soil volume available to the potato plant (due to more extensive root system in warmer soil under the film).

Leaf nitrogen and potassium levels were observed to be higher in the early and later tuber bulking stages. This indicated higher utilisation and/or reduced leaching of nitrogen and potassium.

Final yield data was inconclusive. This was due to a range of unintended non treatment factors such as weed burden and possibly moisture stress impacting on the trial site.

Experience from the above trials providd the researcher with excellent direction for undertaking further research into commercialisation of this film technology. Further research on the impact of film on potato crop development, yield and yield structure was warranted. An estimated yield increase of 0.5t/ha (from use of film) was required to break even and cover film costs. Further assessments needed to also include examination of the effects on crop nitrogen utilisation, and soil moisture dynamics, as the technology had the potential for nitrogen and irrigation savings. Further research needed to include identifying appropriate pre-emergent weed technology to be used in conjunction with the film; and also evaluation of optimum time for film degradation, such that any negative impact of intact film later in the life of the crop could be avoided.