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Potatoes - seedbed preparation | AG0861 |
Kan Moorthy and Andrew Henderson, Knoxfield
October, 1999 |  |
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Soil tillage and seedbed preparation should be done in such a way to ensure not only quick emergence but also deep penetration of the roots and good drainage. Seedbed preparation should start when the moisture content is suitable. Clods formed during soil tillage operations often remain in the ground until harvest. With lighter soils, it is not advisable to make the tilth too fine, because after a heavy rainfall or irrigation the surface tends to seal up and cause severe erosion of the ridges.
The time between planting and emergence is the most delicate period of the potato crop. Emergence is influenced by:
- seed quality (age and sprouting stage)
- soil temperature
- soil moisture
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Planting depth and method of soil preparation affect soil temperature and moisture conditions around the planted tuber. Planting depth should be adjusted according to the soil conditions. Soil in the deeper layers dries out more slowly than surface soil, therefore planting should be deeper in dry conditions. In cool or moist conditions, shallower planting is recommended.
The soil should not be cultivated deeper than necessary. Soil moisture is lost with each cultivation, so the number of operations should be kept to a minimum and performed shortly before planting.
Soil compaction
It is known that the potato has a weak root system and that impermeable layers in the soil greatly reduce yield. For example (from Van Loon et al, 1985 – field trial):
Table 1. Reduced yield due to compacted soil
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Non-irrigated soil, with a slightly compacted layer at ploughing depth
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Non-irrigated soil, with a compacted plough pan
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Soil compaction limits rooting depth and thus the available water. More frequent irrigation is required on compacted soils than on those where the roots are able to penetrate deeply. Another disadvantage of soil compaction and hard layers may be that, after heavy irrigation or rainfall, the soil is saturated for too long, causing roots to die and tubers to rot. It is advisable to break up existing hard layers to avoid soil compaction during tillage operations.
Soil temperature
Potato sprouts grow faster at temperatures above 12º C and up to about 24º C. The optimum temperature for sprout growth is 16-20º C, as shown below (Hogetop, 1930).
Figure 1. Optimum temperature for sprout growth
Higher soil temperatures also promote quick emergence, up to about 30º C. Above this temperature, emergence will be very poor. Higher temperatures allow for deeper planting of seed. At low soil temperatures, shallow planting may be an advantage.
Soil moisture
Soil moisture greatly influences germination of the seed. For example, a trial by Letnes (1958) showed the following results:
Table 2. Effect of soil moisture on seed germination.
| Date | *Normal soil moisture | *Dry soil | *Saturated soil |
| May 10 | 100 | 100 | 100 |
| May 15 | 106 | 100 | 103 |
| May 23 | 110 | 96 | 106 |
| May 29 | 121 | 97 | - |
| June 4 | - | 95 | - |
| June 13 | - | 92 | - |
| Result | All tubers sprouted | Sprouting failed | All tubers decayed |
Note: * % of planting weight of seedpiece planted in: (soil type…)
With normal soil moisture, emergence occurs rapidly and soon after planting the seed produces roots which take up water from the soil. This increases the weight of the seed. In dry soil, the seed loses water and fails to sprout. In saturated soil, the seed takes up water but decays due to lack of oxygen. For this reason, heavy rainfall or irrigation soon after planting is detrimental. Thus, seed potatoes should be surrounded by moist soil, or at least be planted into moist soil.
References
- Hogetop, K. (1930). Botanisches Archiv 30: 350-413.
- Letnes, A. (1958). European Potato Journal 1-4: 27-32.
- van Loon, C.D., de Smet, L.A.H. and Boone, F.R. (1985). Potato research 28: 315-330.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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