Avoid tillage and planting when soils are wet. In general, a field is ready for seedbed preparation when soil in the depth of tillage crumbles when squeezed. Pre-plant tillage when soils are wet can create a cloddy seedbed that reduces seed-to-soil contact. Achieving excellent seed-to-soil contact is essential for rapid and uniform imbibition of moisture by seeds and uniform emergence. Tillage when soils are wet can also create a compacted layer below the depth of tillage that can restrict root development.
Sidewall compaction occurs when planter disc openers cut through wet fine-textured soil, resulting in compacted soil around the seed that is difficult for nodal roots to penetrate. In addition, seed furrows can open after planting in such conditions, resulting in poor seed-to-soil contact.
A planting depth of 2 inches is optimal for corn in most situations in Minnesota. Shallow placement of seed increases the risk of poor nodal root establishment. High planting speeds that result in bounce of planter units and shallow placement of some seeds should be avoided, as this can cause variable emergence and hinder nodal root development.
Risk of inadequate stand establishment is reduced if corn is planted when soil in the seed zone has reached or is near 50°F and is expected to warm.
Maximum corn yield is generally obtained in Minnesota when planting occurs in late April or early May. In years when warm weather arrives earlier than normal, planting in mid-April can produce similar yield if young corn plants are not significantly damaged by a freeze in May.
Optimal planting rates for corn in Minnesota are generally 34,000 to 36,000 seeds per acre. This can vary somewhat with hybrid, soil productivity, and expected yield. Too great of planting rate generally does not reduce corn yield but can reduce economic net return.
More educational resources on corn production are available at Extension's Corn Production website.