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Lentil fertility research finds variable responses

Modest response to phosphorus but variable to nitrogen and inoculants.

March 28, 2024  By Bruce Barker


Phosphorus was the main driver of increased yield in this ADOPT project. Photo courtesy of Chris Holzapfel.

Mind your ‘Ps’ and ‘Ns’ and ‘Is’ when it comes to lentil fertility in the Brown, Dark Brown and thin Black soil zones. Phosphorus (P) can be a limiting nutrient in lentil production, but nitrogen (N) and inoculants can also affect lentil yield and profits. A recent Saskatchewan Ministry of Agriculture ADOPT (Agricultural Demonstration of Practices and Technologies) project looked at these three fertility inputs and how the latter two interact to impact production.

“This project was initiated to demonstrate some of the expected responses to rhizobial inoculation, starter N applications and P fertilization for a range of soil climatic zones in Saskatchewan while also exploring the potential merits of deferred N applications for increasing lentil yields and grain protein concentrations,” says principal investigator Chris Holzapfel, research manager with the Indian Head Agricultural Research Foundation at Indian Head, Sask.

Typically, N fertility is supplied through N fixation with the application of a rhizobial inoculant applied with the seed. Phosphorus can be a limiting factor on low testing soils, while potassium (K) and sulfur (S) are less likely to impact yields on the southern Prairies. The objective of this project, therefore, was to demonstrate the response of lentil to a wide range of fertility management treatments that focus on P rate, rhizobial inoculation and N fertilization.

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The project was conducted in the thin Black soil zone at IHARF, the Western Applied Research Corporation (WARC) at Scott, Sask., in the Dark Brown soil zone, and the Wheatland Conservation Area (WCA) at Swift Current, Sask., in the Brown soil zone in 2021 and 2022. However, drought impacted results at Scott and Swift Current in 2021, and these locations were dropped, leaving four site-years for data analysis. Small red lentil was grown at each site and managed with typical agronomic practices.

Twelve fertility treatments were applied with varying levels of P, N and granular inoculant. These ranged from zero to 60 pounds P2O5 per acre (zero to 67 kg P2O5/ha), with and without N at 49 lb. N/ac. (55 kg N/ha) at sideband or in-season broadcast at the bud formation stage and with and without granular inoculant. Treatments without supplemental N were balanced to supply nine lb. N/ac. (10 kg/ha) across the monoammonium phosphate (MAP; 11-52-0) application rates. Similarly, when N was applied, it was balanced to take into account the amount of N applied with MAP application rates. All fertilizer treatments were side-banded, or in the case of some N treatments, broadcast.

Soil tests found that Swift Current had marginal levels of 15 ppm Olsen-P, while the other sites were quite low in P ranging from two to eight ppm. Nitrate-N soil test levels ranged from 19 to 45 lb. N/ac. (21 to 50 kg/ha).

All sites targeted a seeding rate of 19 seeds per square foot (190 seeds/m2), and emergence, as expected, varied across sites due to environmental conditions. The highest stand establishment was at Indian Head, followed by Scott and Swift Current. At Swift Current in 2022, emergence was about 10 plants/ft2 (100 plants/m2), which Holzapfel says was still a reasonable stand.

“Since all fertilizer was either side-banded or broadcast during the season, we didn’t expect the treatments to impact emergence, and this was the case,” says Holzapfel.

Small but highly significant yield increases to P fertilizer
Yield varied widely by site-year, as expected, with Indian Head-22 yielding the highest at around 55 bushels per ac. (3,700 kg/ha) while Swift Current-22 yielded the lowest at around 28 bu./ac. (1,883 kg/ha). Holzapfel says there were highly significant differences between some treatments.

“Mostly what we saw with the treatments was that yield increased with P fertility. That was the main trend that was evident with yield increases ranging from nine to 14 per cent at responsive sites,” he says.

Swift Current did not show a response to P treatments. Relatively high residual P combined with low yields were the likely reasons.

Holzapfel says the highest and most consistent yield response was at Indian Head, with yield increasing linearly in both years. For example, in 2022, yield increased from 52 bu./ac. (3,509 kg/ha) with zero P plus inoculation to 57 bu./ac. (3,832 kg/ha) with 60 lbs. P2O5 plus inoculation.

At Scott, the P response significantly increased yield up to 20 lbs. P2O5 and then leveled off.

Fertilizer and inoculant treatments evaluated in lentil fertility demonstrations conducted at Indian Head, Scott and Swift Current in 2021 and 2022.
Source: Holzapfel et Fletcher. 2022

Nitrogen and granular inoculant responses varied
Surprisingly, granular inoculant treatments did not affect yield regardless of field history or whether supplemental N was applied. This held true whether the data was averaged across site years and for individual sites.

“I would take this with a grain of salt,” says Holzapfel. “While we did not specifically assess nodulation, this result suggests that background levels of Rhizobium leguminosarum in the soil were sufficient to colonize the roots and facilitate N fixation, regardless of whether an inoculant was applied.”

Holzapfel further explains that all sites had a long history of including peas and/or lentils in the rotations. The most recent pea, lentil or faba bean crop for each site ranged from two years at Swift Current, to four years at Scott and Indian Head. This would have contributed to adequate background levels of rhizobia in the soil.

“However, I can’t look at anyone with a straight face and say don’t use an inoculant,” says Holzapfel.

Lentil yield response to N treatments occasionally occurred, especially to side-banded N, but was inconsistent and not easy to predict. At Indian Head-22, extra N increased yield when no inoculant was applied, as expected. But at Swift Current-22, it was unexpected that the N plus inoculant would provide a yield response. The discrepancy in the N response at Swift Current was likely largely due to random variability. Holzapfel says that across the sites, the response was small but at least marginally significant.

Lentil seed protein content was also an important factor that was measured because of the increasing demand for plant-based protein sources. Protein concentrations varied with location, averaging 26.6 per cent at Indian Head in both years, 24.2 per cent at Swift Current 2022 and 23.8 per cent at Scott 2022. Holzapfel says this could have been more to do with variety genetics than environment as there were no treatment effects of P, N or inoculants on protein content. CDC Proclaim Cl lentil variety was grown at Indian Head, while CDC Impulse CL was grown at Scott and Swift Current.

“Perhaps this result would have differed if we had observed stronger responses to either inoculant or N fertilizer,” says Holzapfel. “However, we must conclude that lentil protein concentrations are more likely to be impacted by the environment, or potentially genetics, than fertility management.”

Holzapfel is currently working on two more lentil research projects. The first is the relative performance of red versus green lentils in soils with high residual N levels. The second is lentil yield response to applications of potash and sulfur fertilizer.

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