Initial Growth (From seedling to the emergence of the 6th leaf)
Initially, plant growth is based on the substances stored in the seed, and in part on the radicle, which supplies the seedlings mainly with water and also with nutrients.
After the 2nd leaf has emerged the plants become autonomous, as the nodal roots gradually replace the radicles and become the ones to supply the plants, while the leaves start to photosynthesize.
Towards the end of this period (3rd-6th leaf), the nodes which will develop into the male inflorescence (tassel) and the ear shoots are formed, and the number of rows which shall include the kernels on each cob is set.
Although the requirements of the crop are low at this stage, the limited root system of the plants makes utilizing the nutrients in the soil difficult.
This is why supplying the necessary nutrients through basic fertilizing early on and close to the roots plays a determining part in the growth and yields of the crop later on.
Fast vegetative growth – flowering (6th-8th leaf)
At this stage the growth of the root system, the formation of new roots, the elongation of the stem, and the emergence of new leaves are accelerated. The plants reach their final height, and the formation of their reproductive organs takes place internally, which will determine the yields of the crop.
Between the 7th and the 12th leaves, ear shoots appear on the axils of the leaves, and the upper two ear shoots shall develop into harvestable ears. By the 12th leaf, the number of rows on which the kernels will grow is set, and the ovules are formed on the rows.
By the 17th leaf, both the highest possible number of kernels that the plant can produce and the final size each ear shoot will reach are set, thus irreversibly shaping the production potential of the crop.
The vegetative stage is completed with the full emergence of the tassel at the top of the plant and the onset of flowering.
During this period of fast growth, the needs of the crops in water and nutrients are maximized. Over 2/3 of Nitrogen (N), 3/4 του Potassium (K), and 50% of Phosphorus (P) have been absorbed by the onset of flowering.
After the 8th leaf has emerged, lack of water and any of the three aforementioned nutrients – particularly Nitrogen – arrests plant growth, limits the number of the leaves and the leaf area, as well as the size of the cob and the number of kernels, and dramatically reduces the production.
Top fertilizing with Nitrogen at the stage between the 5th and 7th leaves is absolutely necessary, and it constitutes one of the most important cultivation practices for crop yields.
From flowering to the filling of the kernels
The reproductive stage begins with the release of pollen from the tassel and the emergence of silks at the sides of the cob, and it is completed after pollination, with the onset of kernel growth in size and weight.
Once pollination has been completed, all the organs of the plant work to “fill” the growing kernels, fast increasing their size and weight. At first, large quantities of sugars and proteins migrate from the leaves and accumulate in the kernels, and then they turn into starch, which gradually solidifies during kernel growth.
Even before the tassel has fully emerged, for the duration of flowering and at the early stages of kernel growth, the requirements of the plants in nutrients and water are great.
From flowering until maturity, the plants continue to absorb 1/3 of Nitrogen (N) and Zinc (Zn) and over 1/2 of Phosphorus (P), which they need throughout their growth cycle.
At the stages of flowering and fruit setting, lack of water will lead to pollen desiccation, delayed silking, deficient pollination, and a smaller number of kernels, which will in turn lead to significantly reduced yields (up to 50 %).
After fruit setting, at the early stages of fruit growth in particular, lack of nutrients and water leads to a reduced size and weight of the kernels, and often even their shedding, which significantly reduce yields.
The requirements in Phosphorus (P) and Zinc (Zn) during this period should be adequately covered by the reserves from basic fertilizing, while the requirements in Nitrogen (N) should be covered by top fertilizing at the stage between the 5th and 7th leaves.
The crops should be irrigated regularly up to shortly before the kernels have hardened.
Corn maturity follows, with the kernels becoming dry and hard. A sign of normal maturity is the formation of a black layer at the tip of each kernel, where the cells die and prevent further starch accumulation in the core.