It’s true that rhizobia bacteria remain healthy in the soil after a pulse crop is harvested, but they lose their edge by the time pulses come around again.
It doesn’t mean the product is bad or it’s the wrong formula; it simply means that time takes its toll on the little bugs, according to BASF’s Russell Trischuk.
“The strains of rhizobia bacteria that growers apply are quite efficient at fixing nitrogen when they go in the ground,” he said.
“But over time, in a two-year or three-year rotation, the cells adapt to life in the soil without their pulse crop. The bacteria themselves only live a few weeks, but the population is constantly re-generating and each new generation is different from the previous generation.
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“The population loses its dependence on that symbiotic relationship with a pulse crop. They just won’t produce as much nitrogen as fresh rhizobia. That’s why the industry-wide recommendation is to use new inoculant every time you plant pulses.”
Rhizobia populations are reduced by environmental stresses, and Trischuk said they require moisture to survive and thrive. In drought conditions, the bacteria die off from thirst.
In flooded soil, water pushes air out of the soil pores and, once again the bacteria die.
Trischuk said BASF’s surveys show that pulse growers are 99 percent behind the idea of fresh bacteria at every pulse planting.
The soybean industry, on the other hand, is 120 percent behind fresh rhizobia.
That number is because the proven benefit of rhizobia in soybean production motivates some growers to do a double inoculant with seed treatment plus rhizobia in the seed trench.
He said some parts of the Prairies, such as the Red River Valley, are prone to wet conditions, which can drown the bacteria, while others areas are drought prone. Doubling up on the inoculant is viewed as an insurance policy.
However, not many pulse growers are doubling up yet on their rhizobia, he added.
Specific rhizobia are required to achieve maximum benefits in any nitrogen fixing crop. The more specific the rhizobia is to the target crop, the greater the benefit to the farmer.
Trischuk said that even within the narrow band of pea and lentil inoculants, different companies sell a variety of different rhizobia.
“Remember that not all inoculants are created equal. Some strains are better at infection and nodulation. The challenge to our chemists is to find the strains that best meet the needs of the target plant,” Trischuk said.
“Some commercial inoculants are aimed at a wide range of crops. They’re not specific to a narrow range of plants, such as pea and lentils. A product that’s more flexible and can be used on a variety of crops means sacrificing efficiency and efficacy.”
