Today managing your corn crop requires knowledge of the different growth stages of the corn plant. Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications. Each week throughout the growing season I will discuss the various corn growth stages and management issue at each stage. This week I will focus on the seed.
The rain continues. By now most of the corn that is going to be planted is in the ground. Due to the weather induced extended corn planting season we have corn at various growth stages ranging from just planted to V4.
The Seed
Now that the seed is in the soil, it will begin to absorb water and begin to swell. Corn kernels must absorb about 30% of their weight in water before germination begins. When enough water has been absorbed and the soil temperature is favorable, germination will occur.
Germination occurs in a specific sequence that is strongly influenced by soil temperature. Therefore, germination and emergence will occur in fewer days when the seed is planted into warmer soils. Corn typically emerges in 115-120 growing degree days (GDD’s).
(Click on each picture to enlarge)
Fig. 1. Kernel appearance 12 hrs after planting.
The radicle root emerges first, near the tip end of the kernel, within two to three days in warm soils with adequate soil moisture or much longer if soil temperatures hover at or below 50F (10C). In cooler or drier soils, the radicle root may not emerge until one to two weeks after planting.
Fig. 2. Seedling appearance 36 hrs (34 GDD) after planting.
The coleoptile (commonly called the “spike”) emerges next from the embryo side of the kernel within one to many days of the appearance of the radicle, depending on soil temperature. The coleoptile is a rigid piece of plant tissue that completely encloses the four to five embryonic leaves (plumule) that formed during grain development of the seed production year. The coleoptile initially negotiates its way toward the dent end of the kernel by virtue of the elongation of the mesocotyl. The plumule leaves slowly enlarge and eventually cause the coleoptile to split open as it nears the soil surface.
Fig. 3. Seedling appearance 60 hrs (58 GDD) after planting.
The lateral seminal roots emerge next and initially elongate towards the dent end of the kernel. Even though these roots and the radicle root are technically nodal roots, they are considered part of the seminal (seed) root system and not part of the permanent nodal root system that develops later. The first so-called “permanent” roots begin elongating from the first node at the crown of the seedling at approximately the V1 leaf stage (1 leaf with visible leaf collar) and are clearly visible by V2.
Fig. 4. Seedling appearance 72 hrs (67 GDD) after planting.
Fig. 5. Seedling appearance 82 hrs (79 GDD) after planting.
Fig. 6. Seedling appearance 105 hrs (103 GDD) after planting.
Fig. 7. Seedling emergence 5 days (114 GDD) after planting.
Fig. 8. Seedling emergence 5 days (114 GDD) after planting.
(Adopted from: Visual Indicators of Germination in Corn, Dr. Bob Nielsen, Purdue University)