Adapting dryland cropping systems for drought conditions
Drought has and continues to be a dominant crop production constraint across the Canadian prairies. The frequency and severity of drought varies between soil zones and even local areas within soil zones. With mounting evidence for climate change and increased climate variability, the risk of drought will likely also increase and the pattern of drought sensitive areas may become more irregular.
Slight to moderate drought occurs regularly in the drier regions of the prairies. Farmers have made significant adaptations to drought through on-going practices which conserve moisture and protect soil from wind erosion. These include drought tolerant crop varieties, no till seeding, conservation fallow, crop residue management, and the seeding of erosion sensitive land to perennial forages.
No till seeding involves placing seed and fertilizer with minimal soil disturbance. Conservation fallow is the use of specialized equipment that conserves crop residue such as wide blade cultivators or rodweeders, or using herbicides instead of tillage to control weeds (that is chemical fallow). Good crop residue management includes leaving taller stubble to trap snow and efficiently chopping/spreading straw and chaff to reduce evaporation losses.
While these practices help to mitigate economic risk, reduced crop yield associated with moderate drought still persists on a regular basis. Under severe drought there is a risk of crop failure and serious wind erosion even when implementing these beneficial management practices (BMPs). Severe drought results not only in short term income loss, but increases the risk of future income losses as a result of soil degradation.Therefore, there is a need to consider additional practices that can help reduce the impact of moderate to severe drought events.
These additional practices can be grouped into three categories:
- Annual adaptation in spring before crop planting
- Annual adaptation in summer after crop planting
- Long-term planning and adaptation.
Annual adaptation in spring before crop planting
Annual adaptation before crop planting hinges on first making an accurate assessment of drought risk based on current and forecasted soil moisture conditions. Early spring soil moisture can be assessed using regionally based soil moisture maps and precipitation data since the previous crop harvest. A more accurate assessment can often be made by local precipitation data, knowledge of soil moisture removal by the previous crop, and probing for depth of moist soil. Producers are aware that these local factors can vary from field to field, and within fields by slope position and soil texture differences. Farmers are managing larger areas of cropland, which may increasingly limit their ability to conduct detailed on-site assessments for every field. However, other tools based on satellite imagery are being developed to assess soil moisture, and may assist producers in the future.
The other half of the soil moisture question is dependent on upcoming growing season precipitation, temperature, and wind speeds. While long-term (that is 1-3 month) weather forecasting has improved there is still a large degree of uncertainty and local variability often related to sporadic summer thunderstorms. Therefore, there is always a significant element of risk, and part of the management decision is based on how much risk a producer is willing to accept.
Following is a list of management options to adapt or lessen the impact of drought in advance:
- Select crop types and varieties that are more drought tolerant
- Select crop types that have lower crop input costs and produce more residue for erosion protection, such as cereal grains
- Reduce the rate of fertilizer application at seeding time, with the option to add supplemental fertilizer after crop establishment if moisture conditions improve
- Increase the percentage of cropland in conservation fallow in the brown or dark brown soil zones, but target fields that have lower levels of soil moisture and adequate crop residue cover for erosion protection
Decisions on implementing these options are often difficult, due to the uncertainty of upcoming growing season precipitation, and a host of additional factors. These include crop prices, crop input costs, available labour and equipment, cash flow resources, previous cropping histories, and outbreaks of weeds, insects, and diseases. Nevertheless, many producers in semi arid regions (that is, brown and dark brown soils) consider these options to a varying degree in most years.
Under a severe drought period that extends for more than one year there are some additional practices that should be considered starting in the second year. The worst case scenario is where a moderate to severe drought is followed by dry fall, winter and early spring conditions. In this situation the risk of severe wind erosion becomes much greater even when applying the above BMPs, because there may be little crop residue production from the previous crop, and little soil moisture available to establish a subsequent crop. Under these conditions a producer could consider the following additional options.
- If soil moisture is at least adequate to initiate establishment, plant a cereal crop at a reduced seeding rate with minimal fertilizer to establish some vegetative cover.
- If soil moisture and crop residue levels are inadequate, begin managing fields using chemical fallow, but leave the option open to establish some vegetative cover if moisture conditions improve by,
- Seeding a delayed cereal crop at a reduced seeding rate.
- Planting narrow annual crop barriers or strips at right angles to the prevailing wind to control wind erosion and trap snow. Strips can include cereals, flax, sunflower, or corn. Weeds in between the strips can be controlled using conservation tillage implements such as wide blades, low crown sweeps, or rodweeders.
Annual adaptation in summer after crop planting
Adaptation to drought after crop planting depends on the stage of crop growth and development when the drought hits. Management options can be grouped into two categories: crop utilization and fallow management. These options can apply to most crop management scenarios, and adaptations made in advance for severe drought will be well prepared for further adaptation if necessary.
Depending on when a crop is seeded and subsequent growing conditions it could be harvested for grain, cut for feed, grazed, left standing with or without a herbicide burnoff, or incorporated as green manure The latter option would normally only be advised if sudden ample precipitation part way through the growing season resulted in heavy growth that could not be harvested.
A number of factors are considered in deciding how to utilize a crop. It is recognized that the impact of drought on pasture and forage production will create a demand for livestock feed using annual crop green feed and even straw residues. This may exacerbate an already high erosion risk by leaving even less crop residue on the soil surface. If possible, livestock producers should plan for carryover feed supplies to lessen the demand for annual crop greenfeed or residues during severe drought. If the crop is short and requires cutting close to the ground for adequate retrieval it is recommended to leave un-harvested strips for erosion protection and snow trapping.
The primary concern of fallow management during a drought is maintaining sufficient crop residue cover for erosion protection. Fortunately, drier weather should result in a slower rate of residue weathering and decomposition, which is normally driven by high moisture and humidity. One may also be able to reduce the number of herbicide applications as weed growth may be less. However, sometimes drought stressed weeds do not absorb herbicide well enough to cause dieback, so allowing some weeds to set seed may be a small price to pay to maintain enough vegetative and residue cover to prevent serious soil erosion.
If moisture conditions improve later in summer, fallow fields with very low residue cover could be seeded to a cover crop or annual barrier strips, as previously described. These can be seeded as late as 4 to 6 weeks prior to fall freeze-up, as long as enough time is permitted for establishment of adequate surface cover alternatively, later weed control operations can be avoided to allow late season growth of weeds and volunteer crop plants, especially if these plants are primarily annuals and a killing frost is able to terminate their growth before they set viable seed.
Long-term planning and adaptation
For annual cropping systems, there are two additional practices that require long term planning but provide long term benefits for snow trapping and wind erosion control. These are field shelterbelts and narrower fields oriented at right angles to the prevailing wind direction. These practices have become more difficult for larger farms with wider equipment to implement, due to increased inefficiencies associated with field fragmentation. Nevertheless, these may be viable options for some farms.
Another long term adaptation option is to convert annual cropland to drought tolerant perennial forage. This practice has been widely recommended for marginal soils and landscapes. It also could be considered as a drought strategy, due to the ability of drought tolerant forage species to survive, persist, and provide much better vegetative cover for erosion protection than annual crops through severe drought periods. This adaptation often requires a change in farming system that involves increased livestock, particularly cow-calf beef production. Within this system it is important to plan for significant carryover reserves of feed or pastures, since yields of forages are also severely impacted by drought.
While the decision to convert annual cropland to perennial forage may be triggered by increasing drought, the timing of this conversion should be delayed until moisture conditions have improved. Forage seeds, being very small, require shallow seed placement and frequent rain showers for several weeks to ensure good germination and establishment. Therefore, significant resolve and long term commitment is required to seed forages during a wet cycle, when the temptation to reap the reward of a successful annual crop in the short term is large.
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