The project was initiated to evaluate agronomic practices that improve marketable yield of sweetpotato.

An 80% yield improvement for cv. Beauregard was achieved using pathogen tested (PT) planting material. Beauregard selections made from grower lines did not give greater yield nor infer improved disease resistance compared with the DPI&F Beauregard.

An initial plant density trial (2001/02) showed no significant effect of varying within row plant spacings (20, 25 and 30 cm) over 9 varieties. A further plant spacing trial (at 20, 25, 30, 35 and 40 cm) on cvv. Beauregard and Northern Star showed no significant effect. The ideal within row spacing is between 25-30 cm. A maturity trial showed the lines Northern Star and L87-59 (Darby) exhibited particularly early maturity (17 weeks after planting).

In 2003 a series of experiments evaluated the effects of varying nitrogen (N) and potassium (K) rates on yield of cvv. Beauregard and Northern Star at three sites. The effect of N was variable suggesting factors other than simply N limited yield. Highest yields of Beauregard were obtained at 50-100 kg N ha-1 at Rockhampton and at 150kg N ha-1 at Bundaberg. At Mareeba yield was reduced at 140 and 210 kg N ha-1 despite the soil having the lowest N concentration. There was no significant effect of K on root yield at any of the 3 sites. Incidence of cracking in Northern Star increased with increasing N rate at Bundaberg but not at Rockhampton.

In 2004 two trials evaluated effects of N (0-250 kg ha-1) and K (0-300 kg ha-1) on yield of Beauregard. Maximum yields were obtained at an N rate of 100 kg ha-1 and at a K rate of 120 kg ha-1. At high N rates yield decreased. The N and K requirements of sweetpotato are not high and application can be reduced.

To test the effectiveness of project research recommendations, technology transfer trials utilising DPI&F best management options were conducted on commercial properties. The results showed that the DPI&F best management options, in particular, utilising foundation seed planting material and controlling nitrogen and potassium usage gave higher marketable yields. Dr. Mike Canon from Louisiana State University made presentations in the three major sweetpotato production areas in Australia outlining current research and production issues in the USA.

Grower surveys were carried out at the beginning and at projects end to evaluate the project impact. All growers surveyed were aware of the project and the greatest impact of the project was in changing their fertiliser usage and the adoption of pathogen tested planting material.

This project has been funded by Hort Innovation, using the research and development levies listed below and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

• Vegetable Fund