Primary symptoms

Planting too deep or too shallow reduces crop establishment. Broadcasting requires more seed.

Shallower seeding speeds seedling growth and increases tillering. (Image by M. Stapper, reproduced from FAO book Irrigated Wheat)

Summary

The shallower the planting depth, the sooner the seedlings can emerge and commence photosynthesis and the earlier that tillering can start. Healthy seedlings can be produced from seed laid on the soil surface. The correct planting depth is one that places the seed where it can imbibe water for germination but not desiccate thereafter. Concerns like protection from birds often make it necessary to plant deeper. Though seedlings of some genotypes can emerge from below 5 cm, this is too deep for many modern genotypes that have short coleoptiles. The plants in the above photograph were sown on the same day but at different depths. It shows that at the same age, seedlings planted shallowly are larger than those emerging from depth. They have many more leaves (15 vs 5) that are shorter and broader, more main shoot leaves (5 vs 3) and more tillers (4 vs 1). Later, these differences will be reflected in spike numbers and yield.

Are the seedlings uniform

• Look over the field within 2 weeks of planting. Do there look to be enough seedlings emerged? Confirm your assessment by using your 1 m stick to count seedlings following the seedling count method (see field sampling).
• Is emergence uniform? If not, dig up a few seeds where emergence is patchy. Have the seeds germinated? If not, check the section on seed viability. Are they healthy? Measure the length of the white, below ground section on emerged plants (see photo at top). This should differ by no more than 1 cm if seeds were planted at uniform depth.
• Is the spacing of seedlings uniform? The mechanical planter may have blocked or over-planted.
• Have any seedlings been uprooted? Look for signs of birds, rodents or insects.
• Check all the suggestions under the section on poor seedbeds.

Causes of planting and emergence problems

• Many of the seeds were dead before planting or had low vigour. Check all the causes under poor viability and poor seedbeds.
• Too few seeds were planted. If broadcasting, many more seeds are required to allow for irregular distribution.
• Seeds were planted too deep for the genotype. i.e. coleoptiles were too short to reach the surface. Measure the length of the shoot between the seed and soil surface. Check this against the recommended depth for the variety.
• Seeds were planted into a seedbed that had dried out leading to uneven germination.
• Seeds were not uniformly distributed, perhaps hand broadcast by an inexperienced worker prior to covering with soil.
• Seeds were planted too shallow and dug up by birds or moved by insects.
• Sowing occurred too long after cultivation allowing weeds to establish and compete with crop seedlings for resources.
• Heavy rain fell after sowing and the soil surface crusted.

What you can do to fix emergence problems?

• Seedbed: Overcome any seedbed and seed problems.
• Seed rate: Follow the recommendations for seed rate for the region.
• Planting depth: Ensure the depth setting on the seeding device is set correctly for the variety.
• Reduce tillage: Use reduced tillage methods or plant direct into residues of the previous crop.
• Pre-irrigate: In the absence of cultivation and seeding machinery, and to achieve good establishment, pre-irrigate the soil, carefully broadcast the seed and fertilizer and cover with a mulch of straw rather than soil (Jongdee 1994).
• Mulch: Apply mulch (disease-free residues) to keep the soil surface moist and cool during seedling emergence and prevent formation of surface crusting. This may also reduce losses to foraging birds, insects or rodents. Mulch is likely to increase yield by around 10% (see Badaruddin et al 1999) but may not be physically feasible or economically viable.