NISKU, Alta. – Farmers concerned about the success of their pulse crops at developing nitrogen-fixing nodules now have a guide available to help determine that.
The nodulation assessment guide was originally developed for use in British Columbia forestry projects, said Kevin Zaychuk, business development manager at 20/20 Seed Labs in Nisku, Alta.
Contractors used small seeded legumes in reclamation projects. Zaychuk, who worked with the B.C. forestry department, found the guide useful.
“It seemed like a bit of stretch going to the Prairies with large seeded pulses, but it was such an efficient guide, so I decided to see if we could make it work in the field,” he said.
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“We were developing a polymer to be used for inoculation of large seeded pulses. To effectively evaluate that polymer in small plot trials and farmer strip trials, we needed a handy guide. That’s how this all came about.”
In reworking the guide, Zaychuk had help from now retired microbiologist Bix Biederbeck from the Agriculture Canada research centre at Swift Current, Sask.
He used the guide on small plots to assess nodulation. Biederbeck found it rang true with what he was seeing in the field.
“We were comparing it to other means researchers had used, like cutting off nodules and weighing them – all sorts of tedious methods you could never get a farmer to use,” Zaychuk said.
“We wanted to make sure it was something farmers could use, or use at a field day, where anybody could do their own assessment without a whole lot of work, equipment or skill.”
The guide suggests the best time to assess nodulation is at early flowering. Nodule numbers and nitrogen fixation rates are generally at the maximum during early to mid flowering.
But Zaychuk said a grower can go out earlier because nodule formation starts about 14 days after crop emergence.
Once assessment timing is established, it’s important to dig up the plants with a shovel. And go easy, said Zaychuk. If the plants are pulled out, the fragile nodules could be lost, which ruins the assessment.
“What we do is go into a field, dig a clump of soil out that has three or four plants in it, then set it gently into a five gallon pail of water. Go on to the next plot and dig that, until you have three in a row.
“Then you go back to the first pail, it’s usually well soaked and the plants come apart from the soil quite nicely. Rinse it in a fresh pail of water. You have roots intact, hopefully with good nodules. Then pick up the guide and assess them.”
The guide looks at two key aspects that deal with the plant and the nodules. With plant growth and vigour, farmers can do a visual assessment.
“That’s easier to do with small plots because you can go back and forth between the check. You have a relative point to compare with. If you’re just looking at one field, you have to make a judgment call.”
The next aspect involves looking at the roots for nodule number and colour. But it’s not simply counting nodules.
“The worst score you can get is zero, where there’s no nodules or the nodules are white or green, which means they’re not fixing (nitrogen). They get zero if there’s nothing, one if there’s less than three groups of nodules or they’re whitish or greenish in colour,” he said.
“Score three points if there’s three to five clusters or groups of predominantly pink nodules. The max score is five, when there’s greater than five pink pigmented nodules. So it’s really straightforward. You don’t have to do a lot of counting.”
Zaychuk said it’s always best to cut the nodules open to check for a healthy pink colour.
“The guide says that if cut open, a strong pink colour is caused by the presence of leghemoglobin, which must be present for active (nitrogen) fixation. If it’s brown, white or green, it’s not effective.”
The last factor to check is nodule position. An assessment can score one, two or three points for mostly lateral, mostly crown or both lateral and crown nodules.
Once those three assessments are made, the farmer adds the numbers. The guide provides three different ranges: unsatisfactory nodulation rates one to six; less effective rates seven to 10; and effective nodulation rates 11 to 13.
Zaychuk suggested farmers should be in their fields early. If they suspect problems, they should talk to their inoculant company to help.
He said Biederbeck recommended that producers check where the nodules form on the plant.
“If the inoculant is seed applied, usually what you’ll see is crown nodulation. If it’s seed applied inoculant, those usually form first. Lateral nodules are along the lateral roots. Those are usually seen when you use a granular inoculant,” said Zaychuk.
“Bix’s opinion was that crown nodules form the quickest and they provide nitrogen to the plant quicker than that lag period when laterals form. We’ve seen that in field trials too, depending on the year. You can definitely see a lag, especially in the green, vigorous plants. Then the granular applied will catch up.”
Early nodulation is important when planting in areas that are usually dry, because spring is the only time the plants have water. Once the soil starts to dry, plants get drought stressed and slough nodules or the nodules desiccate.
The crown nodules tend to go first and the deep nodules, like the laterals, stay on longer. But Zaychuk said there are pluses and minuses to that. Sometimes farmers don’t want a lot of nitrogen fixation later in the year because that can delay crop maturity.
“So often the roots are overlooked in a lot of plants. Whether it’s seed or seedling diseases, damping off, any issues going on below ground, it’s important growers get out, dig up the plants and look at the plants as a whole. This is just one extra tool to see if their input dollars are working for them,” Zaychuk said.
He said the guide is something farmers can use.
“We haven’t pushed it a lot. We work closely with the Alberta Pulse Growers and the Reduced Tillage Linkages, who have been doing work on direct seeding pulse crops. They’ve been looking at inoculation and seed issues with direct seeding pulses. They’ve used it for field days and in newsletters. I don’t know how many growers would be using it, but it’s out there now.”
The guide is available at the 20/20 Seed Lab website www.2020seedlabs.ca. Go to Tech bulletins, then Inoculants and it’s under Pulse Crop Nodulation Guide. It’s available in text and PDF versions. The PDF version includes colour photos.
