By Thom Weir, Senior Precision Agronomist
The weather changes we experience at this time of year makes it difficult to predict when growers will be on the land seeding. Many growers in Western Canada have started to seed. I checked some soil temperatures today and found that the temperatures are already starting to climb.
In a worked-stubble field, the soil temperatures were 5.8°C (42.44°F) and 2.4°C (36.32°F) at the 1-inch and 2-inch depths, respectively. In a fallow field the temperatures were 9°C (48.2°F) and 4.7ºC (40.46°F) for the same depths. These temperatures were taken at 3:00 P.M. Since most crops grown in western Canada will germinate at 5°C (42°F), the temperatures recorded in the fallow field are already near or at that level. Germination and seedling growth are, however, more variable, and slow at low soil temperatures. As temperature increases, germination and emergence become faster and more uniform. Generally, the emergence time is reduced by one-half for every 5ºC increase between 5°C (42°F) and 20°C (68°F). Warmer soil temperatures also result in a higher percentage of plant emergence. The other fact is that the same fields had temperatures of 2.1°C (35.78°F) and 2.7°C (44.6°F) at the 1-inch level at 8:00 A.M.
Several factors influence soil temperatures and the rate of warming. Soil temperature varies with time and depth and is determined by the radiation reaching the soil surface. Frost in the soil will cool the temperature when the sun is not on it. Type and quantity of surface residue, as well as the heat capacity of the soil will also influence the rate of soil heat gain.
Early Seeding Rewards
Generally speaking, early seeding results in maximum yields for most crops. There are several factors that contribute to this:
- Early seeded crops will utilize available soil moisture better. Late seeding will reduce the probability of receiving a given level of total precipitation during the growing season. Environment Canada data from southwest Manitoba indicates that the probability of receiving total moisture based on initial soil moisture is reduced from 50% for a crop seeded on May 1, to 36% if seeded on May 22. As more on-Farm weather data is collected, meteorological information based on your farm, will provide more accurate predictions.
- A heat stress during flowering can negatively impact flowering and subsequently seed set. By seeding early, the crop flowers earlier, thus avoiding the heat that is typically associated with July. This is especially important in canola, as it is very sensitive to heat during flowering.
- Early seeded crops avoid many insect and disease problems by beating the peak infestation or infection period.
- In early seeded crops, there is a wider window of opportunity for timely weed control.
- Early seeded crops have higher quality heavier grain from cereals and higher oil content from oilseeds. Pulses have higher overall quality.
- Early seeding leads to earlier harvesting. Generally, harvesting conditions are much more favorable during August and early September compared to the conditions that follow.
In general, crop yields will increase with early seeding (i.e. mid to late April or early May depending where you farm).
Early Seeding Risks
What about the risks? Frost is probably the biggest risk. Crops vary in their ability to withstand frost. With cereals, the growing point is below ground until approximately the five-leaf stage. This protects the plant from severe frost injury in the spring. The plants may lose above ground leaves but will re-grow from below ground. Other damage can be seen on the tips of leaves or leaf edges which can become yellow and then turn brown and become brittle. Severe injury to cereals where all above-ground matter is damaged can result in a delay in maturity due to the plant having to regrow.
The growing point with canola and mustard is above ground between the cotyledons. Newly emerged canola and mustard at the cotyledon stage can be very susceptible to spring frosts. However, plants emerging while conditions are cold can withstand temperatures 3 (37.4°F) to 4°C (39.2°F) below zero. Plants that are growing in cold -1°C (30.2 °F) to – 5°C (23°F) at the three to four-leaf stage may be even more tolerant. A light frost that burns the leaves may not injure the growing point. To determine the viability of the damaged seedlings, the growing point needs to be green and viable and the stem healthy.
Flax is quite sensitive to frost when it is emerging but becomes more tolerant as it grows. Necrotic wounds called frost canker can be a problem with flax during early stages of growth. These cankers cause disease organisms to enter the plant, leading to death. It can reduce stands by as much as 50 per cent. Damage is most severe in thin stands on light soils and in low spots. Symptoms of frost canker are similar to those of heat canker. There will be plants or areas in the field where the plants have fallen over. At or near the soil surface, the plants will be girdled and have constricted stems.
Peas & Lentils
Peas and lentils have good frost tolerance as they have buds which usually remain below ground during early development. The above ground growth may be severely injured by frost, but new growth will resume from the scale buds.
While most crops will germinate at 5°C (42°F), the speed of crop emergence will increase as the soil temperature increases. While there is an increased risk to frost and poor emergence due to disease, most early seeded crops will out-yield later seeded crops in most years. Keep in mind that crops can tolerate a spring frost much better than an early fall frost. To offset the cold stress associated with early seeding, it is recommended that producers follow these best management practices.
Best Management Practices
- Seed shallow. As moisture is usually ample early in the spring, most crops can be seeded at the low end of recommended seeding depths. This would be 1 – 1.5” for cereals and peas and .5” for canola. This will allow crops to germinate and get out of the ground as soon as possible.
- Use a seed treatment. As germination and emergence is slower at lower temperatures, germinating seeds are subjected to disease organisms on the seed and in the soil for longer periods of time. The largest benefits from seed treatments are seen on early seeded fields. This is even more critical with seed quality being poor this year.
- Use “better” quality seed. Again, for the reasons discussed in the previous point, emerging seedlings need to keep any extra energy that can be given to them in early seeding situations. If you have seed of differing quality, it may be prudent to plant the better seed into the early planting window.
- Apply “starter” fertilizer. Early seeded crops benefit from seed-row applied starter phosphate fertilizer. Yield and maturity benefits from seed-row phosphate are maximized in early seeding situations. If a reduction in rates of Phosphate fertilization is being planned, early seeded crops are not the place to start. As seed-row nitrogen can add additional stresses to emerging crops, do not go beyond recommended rates of seed-row urea applications.
- Early weed control is essential for top yields. If a pre-seeding burnoff is not accomplished due to lack of weed growth, plan to spray early to remove weed competition.
- Oat seeding may be delayed for control of wild oats. However, seeding early and seeding heavy has proven to limit the impact of wild oats in light to moderate infestations.
- Canola that is seeded early will “harden off” and be able to withstand frost below –5o However, extensive frost damage has been observed in areas of the field where heavy trash is present. Only fields with good residue spreading should be considered for early direct seeding of Canola.
- The crops that should be considered first for seeding include canola, barley, wheat, peas and oats.
Over the past 20 years, I have observed that the “optimum” planting dates correspond with the leafing-out of native aspens. By “optimum” I suggest that a producer should try to have at least 1/3 his crop planted by this point – as you can’t plant everything on the optimum date. This “optimum” date has varied from the last week of April to after the Victoria Day holiday. (Note: These observations are from East Central Saskatchewan.)
In recent years producers have experienced a longer growing season, with more frost-free days. In the last five years, the increased frost-free days have come from later fall frosts. However, long term data shows the first fall frost date has remained constant. The lengthening has been due to earlier last spring frosts. Collecting field-centric weather data will allow for calculations such as frost-free days and the average last spring and first fall frosts specifically and accurately for your farm. This information will become more valuable with the years of data you collect.
Whatever your seeding plans are at, I wish you luck in planting this year’s crop.