The foundation for successful maize production is laid early in the season. Maize should germinate quickly and simultaneously for maximum yields. Without a successful start, the crop is already on the back foot and the maximum yield is unattainable. The good news is that there are only four important requirements for quick and simultaneous germination. The bad news is that usually one or more requirements are absent, especially if planting becomes too hasty.
1. Sufficient and well distributed moisture around the seed. Adequate soil moisture is defined simply as not too wet or too dry. Most farmers know what sufficient soil moisture looks and feels like. Poorly distributed soil moisture around the seed can be caused by different soil types, tillage, unusual weather patterns as well as uneven and varying planting depths. Uneven distribution of soil moisture around the seed is the main cause of uneven emergence - yield losses as great as 10% can be attributed to this.
Handy hint During dry planting conditions you should ensure that planting depth is set so that the seed is planted uniformly in sufficiently moist soil. Although the ideal planting depth is between 50 and 60 mm you should not hesitate to plant as deep as 80 mm if that is the depth where sufficient moisture is present. Where furrow openers are set deeper, you should look at how deep the fertiliser will be placed. Be careful not to plant too deeply, especially if using smaller seed sizes. Planting shallower than 40 mm increases the chance of the soil drying out around the seed, which could lead to poor plant population.
2. Adequate and even soil temperature around the seed. Maize will germinate slower and more unevenly if the soil temperature is less than 10˚C. If the soil temperature is 13˚C and higher, maize should emerge within seven days. This is why it is important that there is always sufficient soil moisture available. Fluctuating soil temperatures are caused by changes in soil texture, soil colour, drainage, soil cover by crop residues and poor planter depth control. Temperature fluctuations are critically dangerous when the average soil temperature drops below 13˚C. Hailstorms just after planting can cool the soil down quickly, delaying germination, especially in wet patches.
Handy hint: Dark soils generally warm up faster than light coloured soils. As lands dry out at different rates, the drier parts will usually be warmer than the wet parts. In lands with reduced tillage uneven distribution of crop residues will have a significant effect on soil temperature. The better covered parts will heat up slower than the bare spots. Inconsistent planter depth control causes the seed to be planted slightly deeper into cooler soil than the rest, which can result in uneven emergence. Use custom-made row cleaning equipment attached to the planter to remove crop residue in the row so that the sunlight can heat up the furrow faster.
Example of the effect of soil temperature on the time to emergence in maize.
3. Adequate and uniform seed-to-soil contact. For rapid moisture uptake it is essential for the entire seed to be in contact with the soil. For the closing wheels to work properly, the correct downward pressure for each soil type should be used. If the seedbed is prepared under too wet or too dry conditions clods are formed. Seed-to-clod contact is undesirable. Seed-to-crop residue contact is obtained if the covering layer is still too wet or if the blades of the trash wheel are blunt or incorrectly set. Seed-to-stone contact, needless to say, is not good for germination. Seed-to-air contact should always be avoided. This can be prevented by setting closing wheels correctly.
Handy hint: Row cleaning equipment attached to the planter may be useful for removing crop residues, stones and clods. This helps the planter to place the seed better, cover the kernels and press the soil around them. Other equipment that can help to press the seeds into the furrow will ensure better seed-to-soil contact and uniform seed placement necessary for optional germination.
4. Avoid crusting of the soil surface. Severe crusting of the soil surface or compaction will limit the coleoptile's ability to break through the soil surface causing it to open up underground or die. If the soil is very clayey, the sun’s rays can penetrate between the clods and the coleoptile can open underground.
Handy hint: Avoid excessive tillage of the seedbed just before planting, especially if rain is predicted after planting and before emergence. A powdery seedbed forms a crust very easily. Avoid excessive downward pressure on the closing wheels of the planter, especially if the soil is very wet. In wet conditions the planter’s opening discs can smear the sidewall of the furrow resulting in poor emergence.
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