Early signs looking good in Controlled Traffic vegetable growing

As published in Grower July 2010.

About 12 months ago A. S. Wilcox embarked on a new challenge – to adapt controlled traffic farming (CTF) to their Pukekohe-based cropping operation. A. S. Wilcox is pursuing CTF in order to improve soil quality and overall productivity. They also hope to lower fuel use.

With support from Land WISE and Plant and Food Research, a seven hectare site was allocated to the first year trial; half is being managed according to a CTF approach they have designed, the other half to their conventional “random traffic” practice.

The key is keeping all traffic on the same wheel tracks, never driving on the productive ‘garden’ areas. Under CTF, vehicle traffic is restricted to permanent wheel tracks. These solid ‘roadways’ are better able to carry traffic, allow access sooner after rain and reduce rolling resistance energy demand. The wheel tracks are not removed at the end of a crop, they are retained to carry future traffic. As a result, there is no need for the deep ripping and powered cultivation that is often required to remove compaction caused by random traffic during the season and at harvest.

In this article, crop supply manager Simon Wilcox and scientist Paul Johnstone provide a brief summary of this operation and promising soil indicators measured during the first year.

The trial site is on clay loam at A. S. Wilcox’s property in Pukekawa. The site has been intensively cropped for almost 15 years, typically to their standard 3 year rotation of onions, potatoes and oats. Heavy cultivation has been required to remove compaction and prepare beds for successive crops. Harvesting operations are often difficult in these soils, especially during wet conditions.

There were two key differences in how each half was managed in the first year of the trial. The controlled and random traffic areas both received the same primary cultivation. But there were some differences in the way the onion beds were initially formed (??) and the way the crop was subsequently harvested. In the controlled traffic area, all harvest equipment remained in wheel tracks, whereas in the conventional random traffic area, equipment also travelled on bed tops.

What has been learnt so far?

There was no difference in onion yields achieved using either approach. In time A.S. Wilcox hope the controlled traffic approach will deliver a deeper, better-structured soil that can either support larger crops or require fewer fertiliser or irrigation inputs.

Soil quality of prime interest, so a range of soil physical properties were assessed immediately prior to the harvest of onions in January. These included bulk density, aggregate size and also aggregate stability. There were few big differences in these indicators at this stage, probably because both areas had received the same primary cultivations and all seasonal traffic for weed, pest and disease control was in the formed wheel tracks.

Water infiltration under controlled traffic did however increase by about 30%, an encouraging observation which appeared linked to differences in bed forming practice. This was consistent with visual observations made during the season by the Wilcox team, where the effective soil depth was much greater under controlled traffic.

The most recent set of soil samples were collected in April, just prior to the planting of potatoes. The effects of the different traffic approaches at harvest appear to be emerging. Under the conventional random traffic practice there were a greater number of big, clumpy aggregates – a sign of residual compaction. By contrast, smaller aggregates were formed with less cultivation under controlled traffic.

The current potato crop will give the best indication yet of the potential benefits of the new controlled traffic approach. If these soils are better drained and structured, we expect to see more favourable lifting conditions during the challenging winter period.

In addition to the emerging soil benefits, the Wilcox team estimates they can reduce fuel use by about 50% by managing their traffic. The hoped for energy savings appear to be real. Convinced of these benefits, A. S. Wilcox has increased their controlled traffic area, implementing it on 44 ha this year.

All and all, early observations are encouraging for successful controlled traffic farming at this site!

For more details on these results contact James Powrie (LandWISE) or Paul Johnstone (Plant and Food Research). Funding for this project has come from the Sustainable Farming Fund ‘Advanced Farming Systems’ and ‘Holding it Together’ programs.

The LandWISE website www.landwise.org.nz contains information on current members, articles on precision agriculture and many resources and tools.  It is also a place to comment, chat and ask questions about where to go to learn more.

LandWISE membership puts you in touch with other innovative growers, industry folks and technologists, join at http://www.landwise.org.nz/join/

Visit the website to learn more, or contact James direct on 06 6504531 or 0272 757757.

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