Dry spring conditions combined with aggressive cover crop growth are increasing the importance of early-season irrigation for corn, soybean and other grain producers seeking uniform crop establishment.
Agronomists note that delayed cover crop termination, late spring tillage and limited rainfall can leave soils lacking adequate moisture for planting, seed germination and early root development. In those situations, irrigation before or shortly after planting can help maintain planting schedules while ensuring seed is placed into adequate moisture.
In sandy loam soils, applications of 0.5 to 0.75 inches of irrigation water typically moisten dry soil to a depth of about 6 inches, replacing moisture lost through tillage or cover crop growth. Fields that have received little or no rainfall following cover crop termination may require approximately 1 inch of irrigation. Heavier soils generally require larger applications to achieve similar moisture penetration.
Crop specialists emphasize that newly emerged crops should be closely monitored following irrigation. Maintaining moisture below the surface encourages roots to grow deeper into the soil profile. A dry layer 6 to 8 inches below the surface can restrict crop development and reduce access to water later in the growing season.
Early irrigation also presents challenges. Soil crusting can occur when irrigation is followed by rapid drying conditions, potentially hindering emergence. In those cases, smaller irrigation applications of approximately 0.2 to 0.3 inches may help seedlings emerge through surface crusts.
The issue is particularly significant in double-crop systems. Corn and soybeans planted following forage harvests such as triticale or cereal rye silage often face depleted soil moisture reserves. While newly emerged corn and soybean plants typically use less than one-half inch of water per week, forage crops can extract moisture from soil depths of 2 to 3 feet before harvest.
Without substantial rainfall, producers may need to apply 1 to 1.5 inches of irrigation to replenish soil moisture and support germination and early root growth in second crops.
Early-season irrigation can also improve the effectiveness of soil-applied herbicides commonly used in crop production. Herbicide activation occurs when rainfall or irrigation moves products into the upper soil layer where weed seeds germinate.
In sandy soils, about 0.5 inches of irrigation can activate many soil-applied herbicides if rainfall does not occur within two days of application. Heavier soils may require between 0.7 and 1 inch of water to achieve adequate incorporation. Producers are advised to follow herbicide label directions carefully to avoid crop injury.
Activated herbicides help control the first flush of weeds during a critical period when young crops are most vulnerable to competition. Effective early weed control can reduce the need for later cultivation, hand labor or rescue treatments while improving crop establishment.
Irrigation used for herbicide activation may also help incorporate fertilizer and promote more uniform crop growth. However, producers should be aware that uneven irrigation coverage can create differences in weed control between irrigated areas and dry field corners, making targeted scouting important later in the season.
Nitrogen management is another area where irrigation can play a key role. Many producers apply a portion of their nitrogen fertilizer in late June or early July through fertigation systems that deliver liquid nitrogen through irrigation equipment. Others may apply nitrogen by ground or aerial equipment and rely on irrigation to move nutrients into the soil when rainfall is limited.
As growing conditions become more variable, soil moisture monitoring is increasingly important for irrigation decisions. Specialists recommend monitoring moisture within the crop root zone during early growth stages rather than relying solely on water balance calculations.
For delayed plantings and double-crop systems, soil moisture sensors positioned below developing roots can provide valuable information about irrigation timing. Producers can also use the hand-feel method, where soil below the root zone should form and hold a ball when squeezed if adequate moisture is present.
With many corn and soybean acres entering the growing season under dry conditions, timely irrigation can help improve emergence, support herbicide performance, enhance nutrient management and promote stronger early-season crop development.
Source: Michigan State University Extension, "Water-up and water in: Irrigation can improve production and profits while reducing risk"