The growing season may prove to be more average, but coming off a record dry year, and a dry winter, means planning now for soil moisture retention
by Lyndsey Smith
After a growing season of very limited moisture in Saskatchewan and a below-average snowfall in many areas, pulse growers are understandably nervous about what the soil moisture situation will look like at seeding.
The good news is pulses are well-adapted to dry conditions. The bad news is there is a limit to how well a crop can perform in a drought, and we are headed into a historically low soil moisture situation in many areas.
While no one can predict the in-season rainfall we will get, you can tweak production practices at every step of the crop production line in order to conserve moisture, avoid herbicide carry-over wrecks, and make the most of what is there.
Shannon Chant, Regional Crop Specialist for the Saskatchewan Ministry of Agriculture (SMA), based at Swift Current, says there are at least three pre-seeding decisions to make before you head to the field.
First, take a long, hard look at what is to go on each field. Pulses draw moisture from a shallower depth — 2017 cereal acres may be a better fit for a pulse crop, keeping in mind herbicide carry-over may play a role. Part B to this point, Chant says, is the all-mighty importance of field records. “It does not have to be a fancy app or even on a computer. A notepad works just fine, but keep good records,” she says. Crop types, soil test results, herbicides used, yields — the more details you have, the better decisions you can make under adverse conditions.
Secondly, taller stubble traps more snow and slows moisture loss in the spring. Could you swap some acres around based on potential snow trap? Different crop types have different water use efficiency ratings — this could mean moving more drought tolerant crops on to drier fields or vice versa.
Third, seeding rates should not suffer because of a dry season. Optimal plant stand numbers means the crop — and not weeds — can use what moisture and nutrients are there. Seed size variability can significantly change actual seeds planted per acre if you still use a “bushels/acre” or “standard” seeding rate. Start with a thousand kernel weight of your actual seed and work to a desired plant stand.
Into the Ground
A dry year is all about moisture retention — the more disturbance of the soil, the more water you are going to lose. Tillage is a non-starter, which for those that have been adding it back in to field management, may prove an issue. But for many, the next consideration is going to be the seeding pass itself — where can you conserve moisture?
Nathan Gregg, Program Manager of Applied Agricultural Services for Prairie Agricultural Machinery Institute, says that row spacing and opener selection are really your only two modifiable options. As a general rule, narrower row spacing means more even distribution of seed in a given land area, decreasing the amount of bare ground, hastening canopy cover, and increasing the likelihood of roots accessing what water is there. But narrower row spacing also means more openers relative to wider row spacing, and therefore proportionally higher disturbance of the soil surface.
Row spacing is typically fixed, so the next best option is moving to a narrower, lower disturbance opener to decrease the amount of moisture loss through exposed soil (think knife versus paired row or shovel-type openers). Consideration should be given to seed-placed fertility rates as the seed-bed is narrowed. The seeding pass may require some adjustments, too. Dry soil can be harder to penetrate, requiring more pressure, but a wider opener/tip could cause more fractures and pull up clods of soil. In-field fine-tuning is likely to be the name of the game this year, he says.
Gregg says it is important to recognize that dry soil can be more flowable. “It is possible that the seed gets buried deeper than ideal as granulated soil flows around the opener into the furrow, especially at higher speeds,” he says, which is one more reason to stop and evaluate the job you are doing in the field.
“In a dry year, everything is drier, including the seed you are using,” says Gregg. Handling, moving, and metering dry seed in dry, low relative humidity conditions could result in more cracks or broken seed, so plan accordingly.
At seeding, the depth you chose could make a huge difference on emergence. Some crop types are more forgiving — but there is a limit. A larger seed usually can emerge from a lower depth if it is in to moisture, but a seedling that has pushed up through several inches of soil comes out already stressed and depleted of energy reserves. Of note, soybeans, because of how they emerge, are less tolerant of deep seeding. Crusted soil and compaction will make emergence even more difficult for soybeans. Increasing seeding rates can help soybeans push through crusted soils.
Dry conditions also increase the risk of fertilizer burn from seed-row-placed fertilizers. “Dry conditions aggravate the salt effect of seed-placed fertilizer,” explains Dr. Jeff Schoenau, Professor and Ministry of Agriculture Strategic Research Chair, with the Department of Soil Science, University of Saskatchewan. “Most fertilizers are salts. Too much salt close to the seed can hold back water from the seed, decreasing germination and emergence.”
Under dry conditions, urea and ammonium sulphate fertilizer are likely to generate more ammonia that remains as a gas in the soil, further risking injury to the emerging seedling.
“One option is to redistribute your fertilizer and move more into a band that is separate from the seed-row,” Schoenau says. Remember that published seed-placed guidelines are based on good seed-bed moisture conditions, he says. “If a separate band is not an option, staying conservative with seed-placed fertilizer is your best bet.”
How much fertilizer nutrient you need is best assessed using a soil test, Schoenau says. For example, a dry 2017 means that you might have more residual soil nitrogen in your cereal stubble than you realize, which would reduce or eliminate any need for seed-placed starter.
“Anything that preserves surface residue helps too,” Schoenau says. Residue helps trap snow that fell over the winter, reduces run-off and erosion risk, and helps reduce moisture losses through evaporation in spring and summer.
On the subject of seeding, recognize that nodulation and nitrogen fixation also require water to happen. It is critical that farmers use best management practices for maximum effectiveness of inoculants. Make sure it is stored properly and used quickly, reducing the amount of time from the container to the ground. Placing the inoculant in moist soil is beneficial, if at all possible.
Herbicide Carry-Over and Injury
Besides a lack of moisture, perhaps the biggest risk to a seeded pulse crop is herbicide injury. That is because herbicides are broken down and deactivated through two main processes — microbial activity and hydrolysis — that both require water to happen. It means that carry-over risks may be greater than normal, and potentially cause damage even though you have followed all the re-cropping restrictions.
To gauge the risk of extended carry-over on any given field, it is important to understand what moisture matters when it comes to breaking down herbicides.
Snowfall over the winter does not help, says Clark Brenzil, Provincial Specialist, Weed Control, for the SMA. “Rainfall from June 1 to September 1 is what is going to drive microbial activity and hydrolysis, the two primary mechanisms that break down herbicide actives,” he says.
It is oversimplified, but herbicide molecules that were not broken down in the previous growing season remain in the top inch or so of soil, attached to soil particles. Heavy rainfall presents a greater risk of movement of herbicide residue into the rooting zone. High organic matter and high clay content soils can hold on to more of these molecules, creating a buffer between the crop and the herbicide when rain eventually comes.
A very dry year, such as in the southwest part of Saskatchewan in 2017, actually becomes a non-year when it comes to calculating replant restrictions, says Brenzil.If you used something with a two-year re-cropping interval, such as Authority®, in 2016 and were planning to go back into that field in 2018, Brenzil suggests caution. “The 2017 season would not count as a year because it was so dry. Add a year and rotate into a non-restricted crop,” he says.
If you are concerned about herbicide residue being a problem this year, your testing options are somewhat limited. If you were proactive and took soil samples in the fall, you could send them to A&L Laboratories at London, Ontario, for a full grow-out bioassay test. If you missed that chance, the best you can do for 2018 is gauge your risk based on field history, soil texture and organic matter, and cumulative rainfall.
Brenzil says you could also run in-field bioassay test strips this year that will certainly alert you to any issues within a particular field, but that does not inform 2018’s cropping decisions. If 2018 turns out to be another dry year, however, it could help with 2019 field selection. It is also important to consult with the manufacturer of the herbicide used in 2017 (possibly even 2016) for their recommendations.
If 2018 is also a dry year, in-season herbicide effectiveness could be an issue. Full water volumes and full surfactant loads are key, as weeds themselves will be putting up extra defences, like more waxy coatings or more hairs, to protect against dry conditions. Also, ground water changes could create issues even before the actives mix in the tank.
“As dry conditions go on, mineral in ground water becomes more and more concentrated,” Brenzil explains. A water quality test only takes a week or two and will be well worth it, as minerals, such as calcium, magnesium, and bicarbonate can interfere with product mixing and effectiveness. “Water quality issues can be a pretty easy fix, using ammonium sulfate at different rates for either hard water with glyphosate or bicarbonate problems for the Group 1 “dim” herbicides, such as Poast®, tralkoxydim, or clethodim. There is no reason to not test.”
He adds that a dry weather cycle also causes a shift in weed species (over time C4 plants, such as pigweeds, kochia, and Russian thistle, will thrive), and we already have confirmed herbicide and sometimes multi-herbicide resistance for some of these species. In very dry areas, some farmers may turn to back to summerfallow. Brenzil encourages these farmers to be aware of resistance issues and to watch for misses or trails of weeds that make it through a control pass. “You just cannot let those weeds go to seed,” he says.
Water Efficient Crops
How much water does every pound of crop need? It may seem like a large question, but some neat research recently ranked common Canadian crops by their water use efficiency. Expressed in pounds of yield per inch of water, here is how some crops stack up, in order of more efficient (less water used) to less efficient: