Early Season Pulse Crop Management Decisions After a Dry Year

Dry soil conditions dictate re-examination of some important pulse crop guidelines.

With abnormally high heat and drought conditions occurring over the last year, there is an absence of adequate soil moisture in central and eastern Alberta as we enter the 2022 growing season. Commodity prices are strong and historically we receive much of our growing season precipitation during the months of May and June. So, while there’s reason to be optimistic, we should also proceed cautiously by adjusting some of our pulse crop agronomic practices to comply with existing environmental conditions.

As we enter the growing season, soil moisture deficit, residual herbicide carryover and residual soil nutrients are realities to be considered and appropriately managed.

Faba bean performs better in moist environments under relatively cool growing conditions. While timely rainfalls can reduce overall water needs, average water use requirement by faba bean during the growing season at seven research sites in Saskatchewan was 38 cm (15 inches). Given the plant’s high water demand and the soil moisture deficit entering the 2022 growing season, there is a production risk associated with including faba beans in the crop rotation this year.

Surface soil moisture and time are factors required for breakdown of residual herbicides. Field pea and lentil can be sensitive to some residual herbicide groups while tolerant to others. It’s important to evaluate field histories to assess potential pulse crop damage from such herbicides.

Lack of soil moisture has slowed herbicide breakdown and this delay has also lengthened the time requirement for adequate herbicide breakdown prior to planting specific crops. For example, the product label instructions regarding the replant interval for lentils after application of Authority (a group 14 and 15 herbicide) to a previous crop is 24 months. Given dry soil conditions prolonged the time span for herbicide breakdown, 36 months may be required for adequate breakdown of Authority prior to planting lentils. Such a situation alters a producer’s pulse cropping plans.

For rotational details on all recently applied residual herbicide products on your farm and how they affect cropping decisions in subsequent years, consult the Alberta Crop Protection guide or the product manufacturer. In light of the serious drought affecting many areas of the Prairies and the possibility of additional risk due to more such weather events, some herbicide companies have recently amended specific product labels. In addition to consulting with manufacturers, pulse producers can access a recently published online fact sheet by the Saskatchewan Pulse Growers entitled, “Herbicide Carryover Risks and Considerations”, which features amended product guidelines by the various companies.

Due to lack of 2021 precipitation, crops yielded lower than normal, resulting in less soil nutrient extraction. Under such circumstances, synthetic fertilizers like nitrogen (N), for example, that was applied a year ago did not move much through the soil. Therefore, these nutrients will be present to crop roots in variable amounts in 2022. While this means less fertilizer requirements in 2022, undulating fields will most likely contain variable amounts of nutrients which can only be accurately assessed by soil testing.

Properly inoculated field pea and lentil crops biologically fix most of their N requirements from soil air pockets and therefore do not require much, if any, N fertilization. However, research has shown that high levels of soil available N negatively affects a pulse’s nitrogen fixation process. The plant becomes lazy and instead of fixing its own N, it prefers extracting the inorganic N from the soil. Actual soil N levels near 30 pounds per acre cause a decreased amount of N derived through fixation and it is known that soil N amounts of 50 pounds per acre significantly compromise the pulse’s N fixation process. With this relatively high level of residual soil N and given the current high price of fertilizer, it may be advantageous to consider growing a crop other than a pulse in fields testing uniformly high in N. It would be monetarily preferable to grow pulses in fields testing lower in N to rely on free N fixation for nitrogen needs.

Nonetheless, some pulses may have to be planted in fields with higher than normal N. Research carried out in various soil zones on the Canadian Prairies has shown that the consequence of growing lentils in soils with higher levels of residual N does not negatively impact lentil yield or lengthen maturity. However, with higher soil N, an increase in plant foliage (leaves, stems, etc.) produced a heavier crop canopy, especially under normal to greater than normal seasonal rainfall. A heavier crop canopy results in additional susceptibility to crop foliar diseases. Therefore, if this scenario emerges, scouting for foliar diseases will be of utmost importance in 2022 and it may be necessary to apply a foliar fungicide. Although this research has not been performed on field peas, general belief is that extra soil N would have a similar or greater effect on pea foliage and subsequent disease risk, may extend pea maturity, and the pea plant would be more susceptible to lodging than lentil.

The previously mentioned research with lentils showed that regardless of extra soil N, using an inoculant continues to be important to achieve optimal yield. Although the extra soil N would delay pulse root nodule formation, and some pulse seedling yellowing may initially occur, the seedlings recover quickly. It is believed that the rhizobia associated with the inoculant ensures N fixation provides continuous N to the plant if there is occasional N shortage during the growing season.

Phosphorus (P) is an important nutrient for optimal pulse crop growth and is known to provide a seedling’s “starter” effect. This P starter effect includes facilitation of the growth of vigorous seedlings that assist with weed competition and promotes an extensive root system including the pulse’s nodule formation for optimal N fixation. P also helps ensure earlier maturity and promotes important soil microbiology.

When seeding under good to excellent soil moisture circumstances, the maximum safe rate of actual P application with pea and lentil seed is 15 and 20 pounds per acre respectively in a one inch spread and nine inch row spacing. If the seedbed has less than ideal moisture, which is the prevailing situation this year, seed-placed P is more toxic to the pulse seed. Therefore, under these conditions, apply less P or band P fertilizer away from the seed (side-band or mid-row band).

If you know there is adequate P leftover in the soil from last year, P fertilizer may not be necessary. Due to important soil microbiology that pulses (legumes) uniquely create, they are better scavengers of soil P than other crop types. Beneficial arbuscular mycorrhizae fungi associated with pulses, for example, greatly extend the reach of pulse roots via microscopic hyphae threads, searching a broader range of the soil profile for moisture and nutrients, including P. In this scenario, applying the fungal inoculant JumpStart® (Penicillium bilaiae),may be an option. However, this recommendation comes with a warning. JumpStart® apparently solubilizes soil rock P, freeing it up for plant availability, even though research thus far with JumpStart® reveals variable yield results at the field level. However, with ample P already in the soil, JumpStart® may solubilize adequate early season P to supply the pulse seedling’s“starter” effect.

Neil Whatley, April 2022