Water-up and water in: Irrigation can improve production and profits while reducing risk
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EmailIrrigators have the advantage of applying water to help with germination and emergence and incorporate herbicides and nutrients. When rainfall is limited, irrigation can prevent early-season drought.
Aggressive cover crop growth, and the lack of timely spring rain, may leave fields lacking moisture for optimum planting, seed germination and early crop establishment. Achieving the maximum uniform germination and emergence can often be improved through proper early-season water management. Irrigating fields prior to or just after planting can keep the planter moving and still meet the “plant into moisture” requirement if rainfall is lacking in your area.
Late spring tillage and delays in killing cover crops are two reasons we see drier than normal planting conditions in some fields. Late spring planting of some seed production and vegetable crops fields may result in a greater need for early-season irrigation for developing crops.
In sandy loam soil, irrigation water applied at 0.5 to 0.75 inches will moisten dry soil down to 6 inches to replace water lost to tillage or a cover crop. An inch of irrigation will often be needed in a field that has not received rainfall since the cover crop was destroyed. Heavier soil will take a slightly larger application to wet soil down to the 6-inch level. Monitoring newly emerged crops that were “irrigated up” is essential.
It is important to water enough to keep roots growing down into the moisture. In most years, rainfall is plentiful enough to replenish water lost to tillage or a cover crop, but a dry layer 6 to 8 inches deep can greatly hinder crop development and needs to be replenished by rain or irrigation.
Early-season irrigation can be the cause of and solution to soil crusting and emergence problems. Depending on soil type, crop residue and irrigation application equipment, early-season irrigation can create some soil crusting which can be accelerated by rapid surface drying. Small applications of water, around 0.2 to 0.3 inches, may help to allow emergence of seed through the crust.
Planting after harvesting forages like Triticale or cereal rye silage has the double crop advantage, but rainfall or irrigation is required to replace the depleted soil moisture. Newly emerged corn and soybeans use less than 0.5-inch water per week, but many annuals like wheat and rye will dry the soil to depths of 2-3 feet by the time of forage harvest, leaving the crop dependent on timely rain or irrigation. Unless the forecast promises a significant chance of rain, 1 to 1.5 inches of irrigation is needed to create the moist soil that crops need to successfully grow and root down into.
The same early-season irrigation that supports crop germination and establishment can also be important for activating soil-applied herbicides. In many field-scale vegetable crops, soil-applied herbicides are a key part of the weed management program because they control weeds as they germinate or shortly after emergence. This early control is especially important in vegetables because many crops are slow to canopy, have limited postemergence herbicide options, and can lose yield or quality when weeds compete during establishment. When these herbicides are not activated by timely rainfall or irrigation, weeds may emerge before the product is fully effective, increasing the need for cultivation, hand weeding or later rescue treatments.
Activation occurs when rainfall or irrigation moves the herbicide into the upper soil zone where most weed seeds are germinating. Applications of 0.5 inches of water in sandy soils will activate soil-applied herbicides if rainfall does not occur within two days after herbicide application. Fields with heavier soil will need 0.7 to 1 inch to move the herbicide deep enough into the soil to accomplish the goal. Many soil-applied herbicide labels contain information on improving effectiveness with timely rains or irrigation. To reduce the risk of seedling damage, read the herbicide label carefully to make sure the crop stage of growth is not at risk of herbicide damage.
Having an activated soil applied herbicide in place helps reduce early weed pressure when the crop is most vulnerable. Weed seedbanks can produce repeated flushes when soil temperature, moisture, and disturbance create favorable germination conditions. Controlling the first flush of weeds gives the crop a better opportunity to establish, grow and eventually shade later-emerging weeds. This will also keep escaped weeds smaller and easier to manage if cultivation or other control measures are needed later in the season. In many cases, a timely irrigation event can serve multiple purposes at once by supporting crop germination or transplant establishment, activating the herbicide, incorporating fertilizer, and promoting more uniform early crop growth.
A timely irrigation event can serve multiple purposes at once. It can improve crop germination or transplant establishment, activate the herbicide, incorporate fertilizer, and support more uniform early crop growth. This is especially valuable in vegetable crops, where fewer products are labeled and many crops are sensitive to herbicide injury.
When early weed control fails, later rescue treatments may add cost, increase the need for cultivation or hand weeding, and may still provide incomplete control if weeds are too large. Ensuring that soil applied herbicides are activated is well worth the effort, especially when the same irrigation application can be used to activate your herbicide and ensure young plants have ample moisture. Hopefully, rainfall is sufficient and aligns with your herbicide’s requirements, but if not, a small irrigation application is an investment that can easily pay itself off.
However, irrigating to activate herbicides can also create the problem of different levels of weed control between the dry corners and the irrigated portion of the field. Timely and directed scouting for weed escapes in dry corners will be needed later in the season.
Producers working towards improving both economic returns and groundwater protection often turn towards applying part of their planned nitrogen in late June or early July. This is easily accomplished with liquid nitrogen through the irrigation system, known as fertigation. In some situations, producers may choose to dribble or broadcast nitrogen on the field by air or tractor and use the irrigation to incorporate nitrogen if dry weather follows. This technique is quick, requiring no irrigation equipment modification, but is dependent on the availability of aerial applicators or in-row high clearance application equipment.
Early-season irrigation can be more accurately scheduled by monitoring soil moisture in the root zone rather than using a checkbook irrigation scheduling system for newly emerged crops. Later in the season, checkbook irrigation scheduling will show its advantages over scheduling by soil moisture in the root zone alone. To learn more about checkbook irrigation scheduling, see the Soil Water Balance Sheet and Irrigation Scheduling Tools fact sheets by Michigan State University Extension and Purdue Extension.
Double cropping and late planting of corn or soybeans after the cutting of forages are options that are often limited to irrigated fields. The first or spring crop will often deplete the soil moisture reserves, resulting in the need for irrigation to germinate the second crop. In some situations, irrigation before planting the second crop can aid in seedbed formation. These practices in June and early July are dependent on timely rainfall or irrigation rather than the soil moisture reserves that spring planted crops draw from.
Delayed planting and slow root growth may increase the need for monitoring soil moisture and early-season irrigation. A soil moisture sensor below the developing roots is a good indication of the need for early-season irrigation. More detailed information on soil moisture sensors can be found in the MSU Extension bulletin E3443, “Improving Irrigation Water Use Efficiency: Using Soil Moisture Sensor.”
Soil below the roots should still be able to form and hold a ball when squeezed if adequate moisture is present. The U.S. Department Agriculture offers an easy-to-use guide on the hand feel method of soil moisture monitoring, “Estimating Soil Moisture by Feel and Appearance.”
For more information on irrigation management, visit the MSU Extension Irrigation webpage.
