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Managing Pulses: What Factors to Consider
After observing the moisture conditions and economics present in Western Canada this year, growing a pulse crop can have big advantages. There are many different factors to consider for managing fields to grow a pulse on, including rotation, plant stand management, weed management, herbicide management, residual nitrogen levels, and topography/soil type. Let’s explore some of these important considerations:
Rotation
Crop rotation is one of the most effective ways to help manage root rot diseases such as Aphanomyces in both peas and lentils. Root rot can infect plants at any stage and cannot be stopped once infection has set in. Pulses should only be grown 1 in every 4 years at a minimum. Once Aphanomyces has been confirmed within a field, the crop rotation of peas and lentils should be increased to 1 in every 8 years. Growing pulses on cereal or oilseed stubble is preferred, and they should not be grown on pulse stubble because of increased disease and weed pressure. Be aware of fields that previously had fusarium root disease in a cereal crop or sclerotinia in canola as there would be increased disease risk in the pulse crop.
Figure 1. Pea roots infected with Aphanomyces. Source: Syama Chatterton, Agriculture and Agri-Food Canada
Plant Stand Management
Managing the plant density in a field and knowing if the population is correct is important. If density is too high, disease risk is increased due to the denser canopy and timely fungicide application becomes more important. Fungicide should be budgeted for a minimum of one application, but in wetter conditions, multiple applications may be necessary. There are ways to reduce the amount of fungicide used such as a simple on/off application targeting areas of the field with a denser canopy. Selection of a map to do this can be aided by tools such as SWAT CAM, satellite imagery, or the SWAT MAP itself. Having a discussion with your SWAT CERTIFIED consultant can help decide the best source of data to use for this application.
Figure 2. ON/OFF fungicide application created utilizing SWAT CAM
If density is too low, weeds have a better chance of thriving and there may also be reduced yield potential because pulses are not able to compensate by producing bigger plants the same as other crops might. Higher densities do have benefits by increasing plant competition which can help to compete with weeds. With SWAT MAPS you can fine tune your plant stand to specific areas throughout the field by utilizing a variable rate seed program. Determining the plant stand that best works for your pulses in different soil types and landscape positions can help achieve a balance of yield potential, weed competition, and disease risk.
Weed Management
Pulse crops are not very competitive and do not have the broad spectrum of herbicide options that other crops do, therefore, selection of clean fields is critical. Fields with perennial weed issues should be avoided as there are limited in crop options to control these. Fields that are known to have Group 2 herbicide resistance issues such as cleavers, kochia, wild mustard or wild oat (Group 1 and 2) should be avoided as well. Kochia is a top weed of concern for pulse growers, because with populations that are resistant to herbicide Groups 2, 4 and 9, chemical control options quickly become limited. Harvest can be difficult with higher weed pressure, especially with weeds such as kochia, as weeds often remain green while the crop is ready to be harvested.
Herbicide Management
Dry conditions can increase the risk of herbicide carryover because soil moisture is a key factor in herbicide breakdown. Soil organic matter also influences the effects of soil residual herbicides; organic matter can tie up herbicides and is rich in soil microbes which are responsible for the breakdown of herbicides. At high levels of organic matter, too much herbicide can become unavailable making weed control less effective. On the other hand, low levels of organic matter where there is less tie up of the herbicide allows some herbicides to easily wash into the root zone increasing risk of crop injury. Soil texture can also influence herbicide carryover - higher clay content soils adsorb herbicides making them less available for weed control, while soils with higher sand content have more risk of herbicides leaching into the soil with heavy rainfall that can cause crop injury. Soil pH can also affect herbicides – how quickly it breaks down, how soluble it is in soil solution, and therefore how available it is for root uptake. A SWAT MAP can help clearly define the soil factors discussed previously allowing for better management of your herbicide carryover risk by utilizing a variable rate application as seen in figure 3 where a lower rate was applied on the hilltops to reduce risk of crop injury.
Figure 3. Reducing rates of herbicide on hilltops utilizing SWAT MAP
Residual Nitrogen Levels
Pulses will fix the majority of plant nitrogen requirements if inoculated properly. Pulses grown on fields with high residual nitrogen have the risk of excessive growth leading to lodging, disease and poor nodulation. Research by Guy Lafond at Agriculture and Agri-Food Canada shows that pea fields with up to 54 lbs/ac residual nitrate did not have any impact on yield. Even though fields with high residual nitrate did not have a negative impact on yield it may be economically beneficial to select fields with lower nitrate levels allowing for other crops to take advantage of fields with higher residual levels. Having soil sampling completed by your SWAT CERTIFIED consultant will help provide the knowledge to make a more informed decision how to better match soil nitrate levels to crop choice. With poor nodulation the pulse crop uses higher amounts of nitrogen from the soil and may not produce nodules. This may lead to the plant running out of nitrogen later in the season because they may not be able to fix enough nitrogen. Results from a study done by Bremer et al. (1989) showed that even when high rates of nitrogen were applied on lentils, up to 80 lbs/ac, the inoculated treatments were the highest yielding.
Figure 4. Effect of nitrogen rate on lentil grain yield across 3 Saskatchewan sites in 1987 (Adapted from Bremer et al, 1989)
Topography/Soil Type
Pulses are often cut close to the soil surface during harvest, so, if possible, avoid fields that have large topography changes or lots of rocks to prevent damage to harvesting equipment. Pulses also have lower tolerance to salinity and poor drainage than most other crops so fields with high salinity should be avoided if possible. Select a field with lighter textured soils and good drainage as excess moisture can also delay seed set and maturity, increasing risk of poor harvest quality. SWAT MAPS clearly delineate your field into zones with 1 & 2 being the driest areas of the field all the way to 9 & 10 being the wettest areas of the field. If you have salinity, zones 9 & 10 are likely where it will show. Once a field is mapped and ground truthed selecting the SWAT MAP that best represents the field soil sampling can be completed to clearly define the different soil properties throughout the field.
Figure 5. Progression of root rot symptoms by SWAT zone.
Final Thought
There are many factors when selecting a field to grow a pulse crop on and careful management of these will help to ensure success. Good geospatial data such as SWAT MAPS, SWAT CAM layers, and satellite imagery can be valuable tools to manage these crops for higher returns. Speaking with your SWAT CERTIFIED consultant can help to select fields that are best suited to pulses and help make zone-based management decisions.
