Features Production Research
Tighter broccoli spacing can result in higher yields, problems

When Prince Edward Island cole crop growers approached researchers with Agriculture and Agri-Food Canada (AAFC) at Charlottetown searching for a way to help the industry increase the viability of its broccoli crops, several factors had to be considered when looking for a solution.

When Prince Edward Island cole crop growers approached researchers with Agriculture and Agri-Food Canada (AAFC) at Charlottetown searching for a way to help the industry increase the viability of its broccoli crops, several factors had to be considered when looking for a solution.

While the growers’ major concern was adequate yield, research scientist Kevin Sanderson also had to consider head size and head quality as it pertains to processing and reducing labour costs. On top of that, there had been no research on P.E.I. involving broccoli spacing and growers were in the midst of investing in irrigation.

From 2004 to 2006, Sanderson conducted three seasons of trials using the broccoli variety Marathon, a leading processing cultivar for yield and quality. He conducted the trials under various plant populations and planting configurations (single and double rows), with and without drip irrigation, and using two different planting times.

Sanderson also fertilized the rows with two side dressings of nutrients at two and four weeks after planting.

In 2004, he planted on June 1 and July 20, harvesting from Aug. 3 to 11, and Oct. 21 to 25. The next year, Sanderson planted on June 9 and July 29 and harvested from Aug. 15 to 22 and Oct. 20 to Nov. 6. In 2006, the last year of the trials, he planted on June 19 and July 19 and harvested from Aug. 26 to Sept. 12, and Oct. 3 to 10.

The plant spacing in the three, single row configurations were at 20, 27 and 35 centimetres. The in-row spacing in the double rows were at 35 and 40 centimetres, with the planting staggered in the rows, which were 90 centimetres apart.

The double-row planting proved a bit more of a challenge when it came to weed control, said Sanderson.

In the trials, he examined the effect of plant spacing on stem hollowing, plant height, head diameter and plant spread. He also looked at the effect of planting time on yield.

Sanderson discovered a higher yield was obtained from the earlier plantings, with “a quite respectable yield increase” of about two tonnes per hectare. A 1.5 tonne yield increase was also obtained with the use of irrigation, an increase in marketable yield he estimated at about five per cent.

Sanderson also found there was an increase in yield from 11 tonnes per hectare to 14 tonnes per hectare when the plant spacing in the rows was reduced from 35 to 20 centimetres. But, along with this yield bonus, he also found the planting had a lot more unmarketable plants.

When Sanderson went to a double-row planting, he found a 70 per cent increase in hollowing in the early plants. He also found an increased head weight with greater spacing in the row and a small increase in head diameter when irrigation was used. Decreased row spacing was also accompanied by decreased head diameter and decreased spacing and double rows tended to result in decreased plant heights.

In summary, Sanderson observed higher yields in early plantings plus larger plants and more marketability, but he also discovered more hollow stems and stem browning.

As for irrigation, Sanderson found higher yields and marketability of the broccoli when it was used but more hollow stems. He said there was no effect on stem browning, plant weight or size when irrigation was used.

When it comes to optimal row spacing, Sanderson said a single row with 20-centimetre plant spacing offered the best yield and marketability percentage.

Double-row plant spacing produced smaller plants, he added.

Plant density in Sanderson’s planting configurations varied from 31,746 plants per hectare in a single row with 35 centimetre in-row spacing to a density of 63,492 plants per hectare in a double row with 35 centimetre spacing.

“Although, we see some advantages to higher plant populations, growers must look at the costs of transplants versus yield return,” he said.

A greater plant density requires increased labour and a denser plant canopy may result in increased disease and insect pressures, Sanderson added.