In 2017, Manitoba experienced a lack of precipitation, exhausting the root zone soil moisture in many locations. This was dramatically different from surplus soil moisture experienced in 2016. As we shift our thinking to dry conditions, there are several crop and soil management considerations to keep in mind.
The risk of residual herbicide carryover is elevated in dry years, due to inadequate moisture for the breakdown of chemicals by microbial action. Watch out for products containing clopyralid (e.g., Prestige XC/XL, Curtail M, Cirpreme, Lontrel 360, Eclipse III) in rotations containing peas, soybeans and dry beans, which requires >175mm of precipitation in the year of application for successful microbial breakdown. This breakdown also requires adequate temperatures (20°C is ideal). Refer to the re-cropping restrictions table (pg. 77) in the Guide to Field Crop Protection, herbicide carryover risk map (Figure 1), field records and consult with product labels and reps to ensure your crops are not at-risk of damage from previously-applied chemicals.
Tillage & Field Operations
Minimize the number and intensity of tillage and field operations under dry soil conditions to prevent soil erosion, loss of organic matter and any moisture that is present. This includes product applications (e.g., fertilizer, herbicide) that require incorporation. Direct seeding and no-till are optimal when dealing with dry soil.
High water tables bring soluble salts closer to the soil surface by capillary action. In subsequent dry years, salts are left behind without adequate precipitation to wash them down. It is in these dry years that they can have the greatest impact on susceptible crops. Soil salinity generally reduces root growth, water uptake and overall nutrient uptake. It is also a key player in iron deficiency chlorosis (IDC) of soybeans, along with high calcium carbonate levels, and likely the cause of widespread IDC symptoms in 2017 (Figure 2). Assess soil test soluble salt levels to determine your risk of crop injury. Soybeans and pulses all have low tolerance to salinity.1 For fields that are classified as even slightly saline (1-2 mmhos/cm)2, consider growing IDC-tolerant soybean varieties (Soybean Variety Guide) or more salt-tolerant crops.1
Seeding Date, Depth and Rate
There are three general options for seeding date and depth management in dry soil: 1) dust it in at normal depth and date, 2) seed deeper into moisture, or 3) wait for rain then plant. It is recommended to do what you can to ensure pulse and soybean seed receives adequate moisture for germination. Stick as close as possible to optimum planting dates for pulse and soybean crops, regardless of dry soil. Late planting of early-seeded crops such as peas and faba beans, can cause a serious yield penalty that may outweigh an uneven plant stand due to dry soil. This of course depends on the timing of spring rainfall, but waiting for rain can be a risky practice.
The recommended seeding depth ranges are ½” to 1 ½” for soybeans, ¾” to 2” for dry beans, 1 ½” to 2” for field peas and 2” to 3” for faba beans. Pulse crops have larger seeds and can withstand deeper planting, in general. Therefore, aim to plant at the deep end of each range under dry conditions, or into moisture if possible. Finally, consider heavier seeding rates to compensate for reduced seed survival under dry soil conditions. Seed survival will vary by seed lot, equipment/handling and field. Use the MPSG Bean App Seeding Rate Calculator to determine the most economic seeding rate, while factoring in the appropriate seed survival value.
1 Franzen, D. 2013. Managing saline soils in North Dakota. NDSU Extension Service. https://www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1087.pdf
2 Manitoba Agriculture. 2008. Soil management guide. https://www.gov.mb.ca/agriculture/environment/soil-management/soil-management-guide/pubs/soil-management-guide.pdf