Lentil Inoculation: Optimizing Nitrogen Fixation for Higher Yields

Lentil inoculation involves applying the correct strain of Rhizobium to lentil seeds to maximize nitrogen fixation, a crucial process that enables lentils to meet up to 80% of their nitrogen requirements through natural nitrogen fixation. Lentils form a symbiotic relationship with these bacteria, allowing them to convert atmospheric nitrogen into a form usable by the plant, reducing or even eliminating the need for additional nitrogen fertilizers. Given that native soil strains of Rhizobium may not be efficient enough for optimal nitrogen fixation, inoculation with high-performing strains is essential.

Why Inoculate Lentils?

Inoculating lentil crops with Rhizobium leguminosarum ensures efficient nitrogen fixation, which can significantly reduce the need for synthetic nitrogen fertilizers. Research from the University of Saskatchewan reveals that inoculated pulse crops can fix 50–80% of their nitrogen requirements. While pulses like fava beans are highly efficient (fixing around 90%), lentils fall into the middle range but still demonstrate substantial nitrogen-fixing potential. Despite the persistence of some Rhizobium in the soil, these native strains are often less effective than commercial inoculants, making inoculation a crucial step, especially in soils with low populations of native rhizobia.

Lentil Inoculation and Yield Increase

Field trials and research have shown that inoculating lentils can result in significant yield increases, especially in soils lacking native rhizobia. Yield responses to inoculation have been observed in 30–50% of cases in Western Canada. This variation in yield response underscores the importance of inoculating lentil seeds each time they are planted to ensure the right strain of Rhizobium leguminosarum is present in sufficient numbers to support nitrogen fixation.

Inoculant Formulations

Inoculants are available in three main forms (peat-based powder, liquid, and granular), each with advantages depending on environmental conditions and the application method.

Peat-Based Powder: This formulation is often applied directly to the seed with a non-toxic sticking agent. Peat-based inoculants contain over a billion rhizobia per gram and are effective in retaining moisture, which protects rhizobia under dry seeding conditions. However, they can be messier to handle compared to liquid.
Liquid Inoculants: Liquid formulations are easy to use and allow for precise control over the application rate. They are, however, more susceptible to damage from environmental stress, such as desiccation or exposure to seed treatments.
Granular Inoculants: Granules are applied directly into the soil in the seed row. Granular inoculants provide protection to the rhizobia in dry or cold conditions and are often the most reliable choice under adverse weather conditions. (2)

In terms of performance under adverse conditions, granular inoculants typically outperform liquid or peat-based formulations. In normal conditions, however, all three formulations perform similarly when applied correctly. In regions with no history of pulse cultivation or where flooding or drought has depleted rhizobia populations, double inoculation (applying both seed-applied and soil-applied inoculants) may be beneficial, though this practice is generally unnecessary for lentils if the soil has a reasonable rhizobia population.

Maximizing Inoculant Effectiveness

To ensure successful inoculation, several factors must be carefully managed:

Storage and Handling: Rhizobia are sensitive to environmental factors such as heat, drying, and light. Inoculants must be stored in a cool, dark place before use and should be applied as close to seeding as possible.
Seeding into Moist Soil: Inoculated seeds should be planted into moist soil as soon as possible after inoculation to maximize rhizobia survival and ensure effective nitrogen fixation.
Compatibility with Other Inputs: Inoculants can be sensitive to fertilizers and some seed treatments. Fertilizers should be banded away from the seed, and inoculants should not be mixed with granular fertilizers. If seed treatments are used, the inoculant should be applied after the seed treatment has dried.

How to Check Inoculation Success

The success of inoculation can be assessed by checking the roots of the lentil plants approximately 3–4 weeks after germination. Nodules, which are visible on the roots, are a clear sign of successful rhizobial infection. The nodules should be pink or red inside, which indicates that nitrogen fixation is actively occurring. A lack of nodules, or nodules that are cream or green inside, suggests that nitrogen fixation is either not occurring or has been disrupted.

In conclusion, inoculating lentil crops with Rhizobium leguminosarum is a critical step in optimizing nitrogen fixation, improving crop yield, and reducing the need for nitrogen fertilizers. Farmers can ensure successful nitrogen fixation and sustainable lentil production through careful selection of inoculant formulations, proper handling, and monitoring nodulation.

References

https://saskpulse.com/resources/inoculant-options-for-pulse-crops/
Gan, Y., Hanson, K. G., Zentner, R. P., Selles, F., & McDonald, C. L. (2005). Response of lentil to microbial inoculation and low rates of fertilization in the semiarid Canadian prairies. Canadian journal of plant science, 85(4), 847-855.
https://albertapulse.com/lentil-seeding/