• Soil temperature and soil moisture are variable factors in the first 5 cm, and this can create unfavourable conditions for germination and the formation of nodal roots.
• The formation of nodal roots already starts at V1, and ends at V6; the roots play a major role in the absorption of nutrients and water during the maize plant’s growing season.
• Shallow planting of seeds can lead to rotten plants due to poor development and establishment of nodal roots at V1 to V3.
• Pro-active applications to control good emergence.
• A cleaner plant furrow ensures better seed depth placement and, therefore, better and more even germination and emergence.


Germination and emergence are two of the phases in a maize plant that have the greatest influence on yield. But to understand why, the phases must first be explained. After the seed is planted, it should absorb water and gain about 30 to 35 percent in weight.

The process is known as imbibition. In my opinion, the process is of great importance in ensuring good harvests even in difficult dry years. As germination continues, the coleoptile begins to move towards the soil surface; this is due to the elongation of the mesocotyl. When the coleoptile breaks the soil surface, emergence (VE) has occurred.

Sunlight disrupts coleoptile and mesocotyl elongation, during which the position of the crown and the first nodal roots below the soil surface are established. The crown and the first nodal roots occur at a constant depth, unless the planting depth is exceptionally shallow (less than 4 cm).

See Figure 1 for the difference in planting depth and its effect on the length of the mesocotyl and the formation of the crown and first ring of nodal roots. This positioning of nodal roots plays a major role in the absorption of water and nutrition later in the maize plant’s vegetative phases.

Planting depth – a factor that affects emergence

In Crop Insight, the focus will be on the effect of planting depth and how a producer can make sure, with the help of technology, that he can give each seed the best chance to develop into a plant with high yields.

Planting depth is one of the factors over which the grower has the most control and, therefore, the focal point. The saying “as deep as a matchbox that you turn lengthwise is deep enough for a maize kernel” means that the ideal depth should then be 5 cm. Research conducted by Pioneer in the maize belt of America has shown that maize does not want to be planted shallow, no matter which cultivar is planted. (Figure 2).

Why does planting depth have such a big impact on yield?

Maize prefers a warm climate, so it is produced during the summer. During the summer, there are high temperatures and dry periods during the germination and development of the plant. Not only do dry and hot climatic conditions prevail during the planting and growing of maize, but also wet and cool conditions. The variation in atmospheric temperature has an influence on soil temperature, especially in the shallower parts of the soil.

Wisconsin growers first plant their sandy fields in early spring because the sandy fields dry out quicker than their heavier fields. Sandy soils do not have the water-holding capacity of heavier soils, and therefore there is great variation in soil temperatures, especially in the shallower parts. This means that water is the buffer for large jumps in soil temperature. The reason for this is that water only starts to boil at 100 ˚C and only starts to freeze at 0 ˚C.

A lot of energy is therefore needed to heat and cool water. So, over a long period, there must be a large increase from night to day temperatures for any increase in soil temperature to take place. In 2009, agronomists from Wisconsin monitored the soil temperatures of a sandy soil just after planting, up to and including the first 7 days of an earlier spring planting. The temperature was only measured in the first 5 cm (2 inches).

In Figure 3, it can be seen that there is a large variation in the 06:00 and 18:00 soil temperature measurements (I Saab, 2009). It is indeed an early planting, and temperatures are much cooler compared to summer temperatures. But the principle remains the same; temperatures will only be higher.

The variation in soil temperature in the first 5 cm of the soil has a great influence on the germination and growth of a maize kernel. The first step of germination is water imbibition. After planting, the seed should increase by 30 to 35 percent in weight by absorbing water. The coleoptile, which grows in the opposite direction (towards the soil surface), follows the radicle, or primary root, as it begins to elongate after the kernel swells.

The minimum temperature for the development is 15 ˚C. Lower than this, the metabolic process during germination can no longer take place. This means that coleoptile elongation stops because cell proliferation no longer takes place. Should soil temperatures be above 15˚ C again, coleoptile elongation will take place again. If a kernel is planted very shallowly, especially in sandy soil, it will experience a lot of variation in temperature and moisture during imbibition and coleoptile elongation.

This causes the processes to experience so-called “on and off” periods. This means that growth and development take place when the temperature and humidity are favourable and then stop when the temperature and humidity are unfavourable. The alternation will contribute to the number of days it will take for the shallower-planted seed to emerge compared to the seeds planted closer to the optimum depth.

Plant before variation

During planting, there is a lot of variation in the plant furrow. As already discussed, temperature and moisture are very variable in soil depth, but as the planter unit moves through the soil, it sometimes encounters obstructions such as old maize stubble, clods, stones, and so much more, especially under minimum and no tillage practises. All the obstructions make it more difficult for the planter unit to place the seed at the right depth if the track in front of the planter unit is not cleaned well enough by the planter’s plough knife.

There are many different plough knives (Figure 4) on the market, each with a specific purpose. Although the main purpose of ploughing knives is to make sure that the path is cleaned in front for good seed placement.

During the 2018 to 2019 season, we experienced difficult planting conditions in parts of the summer crop production areas. During one of my trials in Kwazulu-Natal, we made use of a technology option on the planter called Smart Seed Firmer on dry land. The technology provides the producer during planting with a real-time image of different aspects that can be measured by the Smart Seed Firmer.

One of the meetings held that I want to focus on in Crop Insight is “Furrow cleanness.” The marketer of the technology conducted studies on how it affected maize yield (Figure 5).

Figure 5 shows that as the percentage of cleanness in the furrow decreases, there is a decrease in the yield potential of the maize plant.

What causes the decrease in the percentage? As the planter unit moves over the ground and hits an old maize stubble, due to the poor cleaning ability of the plough knives, the maize stubble causes the planter unit to be pushed out of the ground for a second. This causes the planting depth to shift from 8 cm to 4 cm, and even less in that second.

That is why the Smart Seed Firmer reads the planter in that second, for example, at 93% clean instead of 97%. The shallower planted seeds experience more difficult conditions (moisture and temperature), as discussed under the heading Planting depth, – a factor that affects emergence. Figure 6 shows an example of a Furrow cleanness map, compiled by the Smart Seed Firmers.

Just as the company showed that there is a minimum allowable percentage for Furrow cleanness, the trial also pointed out the difference in the difficult production year of 2018 to 2019 (Figure 7).

Planting depth and nodal roots

As soon as the coleoptile breaks the soil surface, emergence occurs. Sunlight disrupts coleoptile and mesocotyl elongation, during which the position of the crown and the first nodal roots below the soil surface is established. The crown and the first nodal roots occur at a constant depth unless the planting depth is exceptionally shallow (less than 4 cm). RL Nielson says that the success of a maize plant’s yield lies in the development of nodal roots, which takes place around V2 up to and including V6.

When the plant reaches the V1 stage, the first nodal root development can be identified (Figure 8a). At the V2 stage, the first set or ring of nodal roots can be seen. Up to and including V6, five rings of nodal roots will be formed (Figure 8b). Maize seedlings’ transition from being nutrient-dependent on the kernel reserves to being nutrient-dependent on the nodal roots occurs around the V3 leaf stage.

Damage or stress conditions to the first rings of nodal roots during the period V1 to V5 can seriously delay a maize plant’s development, and the plant may appear rotten. When we look at the conditions in the shallower parts below the soil surface, they show unfavourable moisture and temperature, and should the seed be planted there, the beginning is already weak. Therefore, planting depth has a great influence on the positioning of the crown with its first ring of nodal roots (Figure 6).

If a maize kernel is planted too shallowly, the crown with its nodal roots will appear very close to the soil surface, and that is where the most temperature and moisture variation occurs. This will have a major influence on the plant’s ability to absorb sufficient moisture and nutrients from V3.

The plant therefore shows rot and will only later recover vegetatively when the roots extend to the deeper parts of the profile. Only then will the plant be able to absorb more nutrients and moisture to meet its needs, but it is already too late compared to plants planted closer to the optimal depth. Figure 10 shows the plants removed to illustrate the uneven planting depth.

In Figure 10, there is a difference in the root mass as well as the difference in the number of leaves between the different depths. From Figure 10, we can then conclude that plants planted at the optimal depth will make better use of the growing season in growing length days than compared to the shallower planted maize. Does it affect yield?


Planting depth has a major impact on the season’s production and should therefore not be taken lightly. That is why it is important that planters components, especially the plough blades, do the job right to ensure that every seed planted has the best possible chance of good production.

As shown in Figure 7, a difference in planting depth caused by the inability of plough knives to clear in front of the planter unit will cause the planter unit not to be able to place the seed at the correct depth, and this will result in a drop in yield, as in the case of the field, from 6,88 tonnes/ha to 4,83 tonnes/ha. The drop was caused by the drop in planter front clean-up from 96% to 91%.


Nielsen, R.L. 1999. Soil Temperature, Corn Emergence and Stand Problems. Chat ‘n Chew Café. Online at

Nielsen, R.L 2013. Root development in young Corn. Chat ‘n Chew Café. Online at

Pioneer Agronomy library. Corn Planting Depth. nomy_research_summaries/pdfs/2014_Planting_Depth_Effects_On_C orn.pdf

Pioneer Agronomy Research Summary Book- Canadian edition 2012. Soil temperature and corn emergence p. 10-12. gronomy_research_summaries/pdfs/2013_agronomy_research_sum mary.pdf

Pioneer Corn; Growth and development manual. p. 11-12.

Saab, I. 2009. Lessons from early planted corn emergence trials. Crop Insights Vol. 19, No. 7. Online at: CONTENT/guid.162E5A10-C690-4C2B-906D-414049D487E6

¹ De Bruyn Myburgh, Field Agronomist Pioneer South Africa