April 14, 2021
Manitoba is currently facing an early, dry spring. Seedbed preparation and planting have already begun for a few farmers, and others are, or at least were, close to hitting the fields. This week’s snowfall has brought some much needed moisture. However, actual precipitation amounts have been variable across the province, ranging from 0.4 mm to 24 mm. To determine how much moisture you received from this snowfall, 1 cm of snow is equal to approximately 1 mm of water. It also depends on your soil moisture status heading into 2021 (see map below).
To help you navigate a potentially dry spring afterward, we have gathered some important points on crop and soil management under dry conditions. Overall, the best approach when facing dry seeding conditions is to enact best agronomic practices that maximize yield potential.
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., Cirpreme, Curtail M, Eclipse III, Esteem, Lontrel 360, MPOWER Battlefront CM, Clobber G/M or Foxxy CM, Prestige XC/XL, Pyralid, Spectrum) in rotations containing peas, soybeans and dry beans. Clopyralid requires >175 mm of precipitation in the year of application and adequate temperatures (20°C) for successful microbial breakdown.
To ensure your crops are not at risk of damage from previously-applied chemicals, refer to the re-cropping restrictions table in the Guide to Field Crop Protection (pg. 84), check your herbicide application records and consult with product representatives.
Minimizing the number and intensity of tillage and field operations will help conserve soil moisture. This begins with reducing or avoiding pre-plant tillage. Any type of tillage results in higher evaporative water loss compared to untilled soil (Figure 1). Each cultivator pass in the spring can remove approximately 10-12 mm of water from the soil.
Figure 1. Average soil moisture levels from thaw to canopy closure to a 2-inch depth under four tillage systems in North Dakota and Minnesota. Source: Upper Midwest Tillage Guide Part II
Recent findings from AAFC and U of M research have shown that, in most cases, soybeans yielded similarly and performed well regardless of residue management method ahead of the soybean crop, including no-till and min-till methods.
Seeding Depth, Date, Rate and Row Spacing
You may be considering the following options while dealing with dry soils at seeding time: 1) to dust it in at an optimal depth and date (Table 1), 2) to seed deeper to access moisture or 3) to wait for rain, then plant.
One part of launching a good crop is to ensure the seed has access to adequate moisture for germination. Under dry conditions, it may be tempting to drive seed deep to access soil moisture. However, this decision depends on the crop type and how deep the soil moisture is.
It is best to remain within the optimal seed depth range. For soybean and dry bean seedlings that need to push their cotyledons out of the ground, seeding deeper than the recommended maximum is risky. According to research on soybean seed depth conducted by Kristen MacMillan (U of M/MPSG), seeding deeper than 1.75 inches can delay emergence and increase seedling stress (e.g., hypocotyl swelling, loss of cotyledons). Note that this research was conducted under dry conditions from 2017 to 2019.
It is risky to wait for rain to plant. Prioritize planting of cool-season crops first (e.g., peas, faba beans), then plant the warm-season crops (e.g., soybeans, dry beans). Aim to plant all crops at the earlier end of the recommended window to access the topsoil moisture that is there (Table 1). Research in Manitoba has shown that the soybean seeding window is quite flexible throughout May, and that earlier planting dates offer the best yield potential. But you’ll still need to watch your frost risk. A good rule of thumb is to plant within two weeks of your last expected spring frost date.
Consider the impact dry conditions might have on seedling survivability. Adjusting seeding rates to still achieve optimal plant stands will help you maximize yield potential (Table 1). Use the MPSG Bean App Seeding Rate Calculator to determine your most economic seeding rate.
Finally, planting in narrow rows will help your crop achieve rapid and effective canopy closure, reduce evaporative water loss during the growing season and protect yield potential. Recent Manitoba research has proven that both soybeans and dry beans perform well in narrow rows, and in some cases outperformed those grown in wide rows. Narrow rows are a must for peas and faba beans.
Fertilizer can cause damage through either salt injury or ammonia toxicity. Symptoms of fertilizer burn include dark grey or blackened seeds or roots. The drier the soil, the greater the risk of fertilizer burn – especially if it is placed in the furrow.
The amount of fertilizer that can be applied safely depends on the crop species, type of fertilizer, fertilizer rate and soil type, in addition to soil moisture. A fertilizer with a higher salt index (e.g., K2O = salt index of 116, MAP = salt index of 27) or one with a greater ability to produce free ammonia (e.g., urea) will increase the risk of fertilizer burn. However, pulse and soybean crops are very sensitive and dry conditions greatly increase the risk of injury, regardless of the product.
In dry years, soluble salts may be left near the soil surface from previous moisture and capillary rise. It is during dry years that salinity can have the greatest impact on susceptible crops. Soybeans and pulses all have low tolerance to salinity. Soil salinity reduces root growth and both water and nutrient uptake (e.g., soluble salt is one of two key players in the expression of iron deficiency chlorosis, along with calcium carbonate content).
Refer to soluble salt levels from your most recent soil tests to determine your risk of crop injury. Avoid planting soybeans, field peas and faba beans on fields with soluble salt levels >1 mmho/cm, and >0.8 mmho/cm for dry beans. Refer to the latest Soybean Variety Guide to find a tolerant variety that is suitable for saline, IDC-prone fields.
References and Additional Resources
Manitoba Pulse and Soybean Growers. 2019. Residue management for moisture conservation.
Lawley, Y. 2018. Decisions about soybean residue management. Pulse Beat article.
Mohr, R. 2021. Early season management of soybeans. Pulse Beat article.
Manitoba Pulse and Soybean Growers. 2018. Agronomic management of soybeans in Manitoba: Row spacing and seeding rate. Pulse Beat – The Science Edition article.
Manitoba Pulse and Soybean Growers. 2021. Evaluating row width and plant density for dry beans. Pulse Beat – The Science Edition article.
Bohner, H. 2018. Is there a Safe Rate of In-Furrow Fertilizer for Soybeans? Grain Farmers of Ontario Field Crop News article.
Franzen, D. 2013. Managing saline soils in North Dakota. NDSU Extension Service.
Manitoba Agriculture. 2008. Soil management guide.