Late planted seed corn and replant commercial corn and soybeans can benefit from irrigation if dry soil conditions exist. Achieving the maximum uniform germination and emergence can be assured 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 the delays in killing cover crop are two additional reasons we see drier than normal planting condition in some areas. Wet, mid-spring conditions has delayed fieldwork and recent dry spells in some areas have led to crop emerging into dry condition. Late planting may result in a greater need for early June irrigation for developing crops as we enter into the typical drier weather of summer.
Irrigation water applied at 0.5 to a 0.75 inch will wet dry soil down to 6 inches to replace water loss to tillage. An inch of irrigation will often be needed in a field that has not received rainfall since the cover crop was destroyed. Monitoring newly emerged crops that were irrigated up is essential. It is important to water enough to keep roots growing down into the moisture. Most years’ rainfall is plentiful enough to replenish water lost to tillage or cover crop, but a dry layer 6 to 8 inches down can greatly hinder crops development, and needs to be replenished by rain or irrigation.
Early season irrigation can be the cause 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 accelerated by rapid surface drying. Small applications of water 0.2 to 0.3 inch may help to allow the emergence of seed through the crust.
Planting after harvest forage like wheat hay or cereal rye silage has a double advantage, but rain fan 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 a depth of 2 to 3 feet, leaving the crop depended on timely rain or irrigation. Unless the forecast promises a big chance of rain, 1 to 1.5 inches of irrigation is needed to create the moist soil crop need to develop into.
Many herbicide options can be assisted by a timely rain or irrigation. Applications of 0.3 to 0.5 inch of water will move activated soil applied herbicides if rainfall does not occur within two days after herbicide application. Irrigating in 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 weeds in dry corners will be needed later in the season.
Early season irrigation can be more accurately scheduled from monitoring soil moisture in the root zone rather than 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. Here are some resources to help you learn more about checkbook irrigation scheduling:
Delayed planting and slow root growth may increase the need for monitoring soil moisture and June irrigation. Soil probing below the developing root is a good indication of the need for early season irrigation. Soil below the roots should still be able to form and hold the ball when squeezed if adequate moisture is present. USDA offers an easy-to-use guide on hand-feel method of soil moisture motoring.
Source: Lyndon Kelley, Michigan State University Extension