Good Reasons to Sample Soil

Monday, June 26, 2023

Spring soil sampling may prove to be especially beneficial.

By Paige Kennedy

As spring arrives here in Western Canada, producers are finally getting out in their fields. While seeding has started for many growers, one consideration now is spring soil sampling.

Soil sampling, and subsequent soil tests, can give producers a good idea of the available nutrient levels or supply rate of nutrients, pH, and organic matter content on the field depending which soil lab is selected. Basic soil test results provide an index of soil nutrients and rank nutrient availability from very low to excessive or provide pounds of each actual nutrient per acre; or express the actual nutrient level in ppm (parts per million) per acre or provide a supply rate for each nutrient. Having your hands on this information can help manage fertilizer application rates to properly correct any nutrient deficiencies for each crop plans for the season ahead, and ultimately help protect your bottom line.

Provincial specialist in soils with the Government of Saskatchewan, Ken Panchuk (PAg) says "soil testing to determine nutrient levels is an important step for 4R nutrient stewardship and optimizing returns from the dollars invested."

The 4Rs of nutrient stewardship that Panchuk refers to are: Right source, Right rate, Right time, and Right place. The 4Rs are a framework that encourage farmers to match nutrient supply with crop demand, while minimizing nutrient loss from the field, with the aim of achieving cropping system goals. Implementing regular soil testing practices on their operations will better equip farmers to follow the 4R framework and manage their soils effectively.

Regular soil testing gives producers insight into the long-term fertility of their land and can be helpful in diagnosing crop production problems. While sampling yearly would be ideal, the expenses can add up. Sampling at least every third year is the common recommendation in Western Canada.

Keeping records of your soil test results over time is a great way to track responses and identify trends in nutrient levels based on field management and fertility plans.

Since spring is a busy time on farms across the Prairies, common practice is to soil sample in the fall – post-harvest and prior to freeze-up. However, if you have the time and labour available, there are a few cases in which spring soil sampling may prove to be especially beneficial.

As Panchuk says, "I encourage farmers and industry representatives to conduct spring soil sampling, especially if they didn't get around to soil sampling before freeze-up last fall, or (if they) have a few lab results that are difficult to explain and need resampling."

Sampling frozen soils is not recommended because of the challenge of getting the soil probe to depth. As such, getting truly representative samples on frozen soils is not likely.

Additionally, many regions of Western Canada experienced an exceptionally dry fall to finish off the 2022 growing season. Panchuk points out that those fields that missed the rains would have been too dry to sample in the fall and could benefit from soil sampling this spring once the snow melts and the soil thaws.

Logistically, spring soil sampling some fields and fall sampling others could help spread the workload between fall and spring.

Of course, to keep records consistent it is recommended to keep your spring-sampled fields the same over the years, and to keep the fall-sampled fields the same too.

Plant-available nutrients can change considerably over the course of the winter, especially in warmer years or in regions with fluctuating temperatures, such as in the Chinook region in southern Alberta. The warming and cooling of soils over the course of the winter can encourage nutrient mineralization, as well as increase the possibility for nutrients to escape via leaching, runoff, and denitrification. These processes can change the nutrient dynamics of the soil. In these cases, spring soil sampling will give farmers a more accurate assessment of the available nutrients in the field come seeding time.

Panchuk emphasizes that the dry conditions that led to a lower 2021 crop yield, followed by another lower-yielding season in 2022 in some areas, has an impact on our soil sampling and fertilizing practices. He explains that nutrient application rates are calculated based on realistic target yields for crops and stored soil moisture, as well as expected precipitation during the upcoming growing season.

Due to the past couple dry years we've had in Western Canada, the crops that failed to reach their target yields also did not efficiently use the applied nutrients. That means that higher soil residual nitrogen levels are likely this year. Collecting soil samples down to a depth of 24 inches this spring would be useful to see if and where that leftover nitrogen might be sitting. This will help farmers plan for the 2023 growing season and help mitigate the environmental and economic risks associated with fertilizer over- or under-application.

Soil sampling can be done a few different ways regardless of what time of year it is done. Farmers can block their land by specific field, by zone, or by benchmark sampling, whereby farmers sample from a representative part of their field.

Farmers should take 20 to 30 soil cores per area and composite the samples based on the field, zone, or benchmark area. Based on academic research in the 1990s, it was determined that 30 samples are the minimum required to get a good average sample to send to the lab.

Ideally, soil samples would be taken at three depth increments: zero to six inches, six to 12 inches, and 12 to 24 inches. Multiple increments would give farmers the most information on nutrient abundance throughout the soil profile. However, the time and labour involved with sampling at three depth increments is likely inhibitory.

Les Henry, retired professor and extension specialist from the University of Saskatchewan and a well-known entity in the world of soil science, advocates that the best and most practical sampling program is to sample to two depths: zero to six inches and six inches to either 12 or 24 inches. Whether you decide to sample to 12 or 24 inches, ensure the depth remains consistent from year to year.

Once samples are collected and composited, growers should spread the soils to completely air-dry at room temperature and then pack them up to be sent to the lab.

For some specific testing, labs may require field-moist soils. In such cases, soils should be sampled and placed directly in a cooler with ice to maintain the integrity of the soil biological composition. The field-moist soils should be maintained at 5 C or cooler and arrive at the lab the following day.

If spring soil sampling sounds like something you'd like to consider, Panchuk encourages that "soil testing labs do gear up for a rush of samples in spring just before seeding starts, so contact the lab ahead of time to ensure quick delivery of your soil samples and return of your sample analysis on time for seeding."

Happy sampling! BF

Prairie snow melt update

The Government of Manitoba predicted typical spring flooding of the Red River with the flood risk moved from moderate to major risk. However, floods were not expected to evacuate communities this year. Highway 75 between Winnipeg and the U.S. is expected to remain passable throughout the spring and early summer.

Earlier in March, the Water Security Agency released their most recent Spring Runoff Report. In Saskatchewan, growers in the south can expect another dry year due to dry soils at freeze-up and a limited snowpack over the winter. Snowmelt events throughout February mean that soils were already snow-free in many places in the south in March. Across the province, spring runoff is expected to be within the near-normal to slightly above normal range for most areas. Snow melt was expected to be gradual.

Albertans expected a gradual snow melt this year too. Central Alberta was on track to get slightly above average snowfall this spring, with cooler than normal April temperatures. Temperatures are predicted to be higher than normal in May. Growers in the southern part of the province missed a lot of the rains last season and had snow-free fields into January this year.

Across Western Canada, plenty of growers remain in a water deficit from the past few dry years. Many farmers hoped for a slow spring melt and enough spring rains to replenish the dry soils. BF