Conserving Soil Moisture
With harvest underway in the prairies, the yields are reflecting the lack of moisture the 2021 season has brought. Most of Saskatchewan has experienced drought conditions this year and many regions have been experiencing it for the past couple years now. The below average moisture has reduced crop yields as well as crop biomass, affecting both grain and livestock producers. As combines roll and fall work begins, there are several management strategies we can practice to manage these conditions in the smartest possible way and conserve moisture for the 2022 crop.
Some management practices to consider this season to conserve and rebuild soil moisture are:
1. Reliable Soil Tests - Our SWAT MAPS clients are seeing the value of reliable soil tests by zone as they question how much nitrogen and sulphur will be left after this growing season. Will there be higher than average residual across the farm due to lower yields? Will there be 80 lbs/Ac nitrogen on the zone 1-2 hills, but 10 lb/Ac in the zones 7-8 non-saline depressions where there was enough moisture and decent yield? With fertilizer prices as high as they are, it will be invaluable to know these answers.
2. Stubble - Leave stubble and leave it as tall as possible. Many people with cattle may want to bale it but try to leave it tall enough to catch snow. Some producers may be thinking about straight cutting more acres this year due to shorter crops but try to keep it as tall as possible while doing so. The taller stubble will trap more snow in the winter and will help replenish soil moisture for the spring. Figures 1 and 2 below show 5” stubble vs 10” stubble as an easy way to visualize how much more snow the 10” stubble would be able to trap.
3. Fall Field Work - Reducing the amount of harrowing, tillage, or other events that disturb soil in the fall will prevent the soil from drying out further. It will be important this year more than ever to preserve the stubble that is left after harvest (even if it is a minimal amount). If you do need to harrow, leave the hills that are the most prone to water runoff, leaching, and soil erosion. The stubble not only catches snow to preserve moisture, but also reduces evaporation and holds the soil in place, as demonstrated in Figure 3.
3. Residue/chaff management - Crop residue prevents evaporation, protects the soil, and aids infiltration. By evenly spreading chaff from the combine across the field, a producer can increase the albedo rating of the fields surface and ultimately reduce evaporation from the soil. Producers can accomplish this by making a pass with a light harrow, or “lay down” the tines on a heavier harrow. Making passes with heavy harrows will break up straw and chaff, blackening up the soil surface and reducing snow catch.
4. Fall Fertilizer - Can we get away from it and move to one pass, zero till? If not, switching to a narrow opener will be important. Broadcasting fertilizer is also an option.
5. Fall Weed Control – Always important but especially now as every ounce of moisture we have, we need to be there for the crop next year and not be used up by weeds. Many fields this year did not receive a pre-harvest application and it will be important to assess each field for weeds and spray post harvest if they are there (especially after rain). The early harvest and dry conditions mean we might not have had a good kill on some perennials and winter annuals at pre-harvest timing, or might have significant regrowth. The pea stubble last fall in Figure 4 had severe volunteer wheat and wild oats at the 4 leaf stage by September 10. It was sprayed shortly after as the area was extremely dry and there was no frost in the 14 day forecast that would kill them off.
7. Other Considerations - these won’t necessarily help conserve moisture but are important to consider after a dry year are herbicide carryover and cropping plans. We are seeing more crop injury due to herbicide carryover in these dry conditions. Be mindful of fields that used residual products or have high carryover risk and re-cropping restrictions. Consider this as you think of next year’s herbicide plan as well. In planning for next year, also consider crops that struggle more in drought conditions such as faba beans and barley.
These ideas are not new or surprising, but we feel it is important to discuss them and try to apply as many as possible in a dry cycle. If we are headed into more dry years, every small thing we can do to conserve moisture will make a big difference. It will be important during and after harvest to keep the stubble tall enough to trap snow, keep fields clean of weeds, and keep soil disturbance to a minimum, but if fieldwork needs to be done try to preserve as much of the stubble and chaff layer as you can. Using reliable soil tests from SWAT MAPS will help manage the possibly variable N+S residuals in the soil as we plan for the 2022 crop.
Senior Precision Agronomist