Soil Requirements and Preparation for Sweet Potato Growing
Where to plant sweet potatoes
Sweet potatoes generally have similar soil requirements to other vegetable crops. The plants thrive in sandy to loamy, moderately deep soils with proper aeration and drainage. Fields with high clay content, fine loams, and high water tables should be avoided. Sweet potatoes are sensitive to excess moisture and water-soaked conditions. The plant can tolerate a wide range of pH levels from 5 to 7. However, the optimum levels are around 6. To define all these, farmers are advised to perform a soil analysis before planting their crops.
The necessary soil preparation starts 1-2 months before transplanting sweet potato slips. Farmers remove or incorporate any previous crop residues and weeds and plow well at that time. Plowing improves soil aeration and drainage. At the same time, plowing removes rocks and other undesirable materials from the soil. After a few days, and if the soil has proper humidity levels, they till the land. It is essential to leave the soil finely tilled without any big combined lump to avoid problems on cultivars’ roots. Limestone or dolomite may need to be applied (broadcasted) based on the soil analysis results. Remember that 240 kg (or 530 lb) of lime and 400 kg (or 880 lb) of dolomite are needed to raise the soil pH by 0.1 unit. In case the field has an extended problem, especially with persistent perennial weeds, many farmers apply a pre-emergence herbicide, always after consulting your local licensed agronomist.
A week later, many farmers apply a basal fertilizer such as well-rotted manure or synthetic commercial fertilizer (5-20-20 or 6-9-15 N-P-K). They apply everything after examination or their soil test results, and always after consulting a local licensed agronomist. Most farmers integrate the fertilizers on the same day, using tillage tractors. Some producers prefer to apply them only across the planting rows, while others apply them on the entire field. In case drip irrigation is used, some farmers prefer to combine the first watering and fertilization with fertigation (a solution of 10-34-0 N-P-K).
Producers traditionally grow sweet potatoes on hills, raised mounds, and ridges (banks). They create hills 30-60 cm (12-23 in) high and 40 cm (16 in) wide to keep the developing roots covered under the hills. Usually, the distance between the hills is around 60-90 cm (2-3 ft). Keep in mind that if mechanical harvest is used, the hill distances should be matched to the width of the digger tractor-mouth. Furthermore, a roadway should be formed every 6 rows to allow machines to pass through the field (for agrochemical applications).
If soil analysis has revealed soil infection problems, some farmers apply soil disinfection substances through the irrigation system (ask a licensed agronomist in your area). The next and most crucial step (especially in countries with non-optimum soil temperature during the planting period) is mulching with linear polyethylene coating or organic/natural mulches. Many producers cover the rows with black or green Infrared – Transmitting (IRT) or black plastic film. They use this technique to maintain the root zone temperature at optimum levels (21-27 °C or 70-80 °F) and prevent weeds’ growth. These conditions may allow earlier planting of the crop, but the plastic mulch should be removed when the temperature rises.
Sweet Potato Planting and Plant spacing
The planting time highly depends on the location and local environmental conditions. Remember that sweet potato is very sensitive to frost and need around 4-5 months of warm temperatures to yield high. As a result, farmers of the southern hemisphere in areas with heavy frost may transplant the sweet potato slips-cutting from mid-November to early December. On the other hand, if there is no frost danger, the best period for transplanting is from January to March. By selecting the first growing period, they eventually harvest from April until May. By choosing the second growing period, they elongate the harvest period and harvest until winter.
Time depends on the storing conditions and the intensity of the light. Sweet potato vine tip cutting (or slips) remain in seedbeds for 1-2 months before transplanting in their final positions. Larger cutting usually gives higher yields, but farmers prefer slips of 20-25 cm (8-10 inches) with approximately 5-8 nodes and a sufficient number of leaves for transplanting.
After all the preparation steps, the grower begins transplanting the plantlets. Growers label the exact points where they will plant the young plants on the hills, which sometimes are covered by polyethylene mulch. They then dig holes and plant the slips. They plant them at a 30-40º angle. This angle promotes proper root growth. Growers cover half of the cutting or 3 to 5 nodes (around 4-5 cm or 1.2-1.5 in of the cutting should remain above ground). Planting can be done either manually or mechanically using mechanical planters. The sweet potato farmer buries a bit more than half of the cutting’s nodes. Avoid planting them too deeply because harvesting will become more difficult. Usually, more than 1 cutting is placed in each position.
A pattern many growers suggest for sweet potato planting is to keep: a 30 cm to 50 cm (12-20 inches) distance between the plants on the row and a 0.7 m to 1.5 m (2.3-5ft) distance between rows. Usually, a planting depth of 10 cm (4 in) is used. Following these patterns, we will plant approximately 30,000-60,000 slips per hectare or 12,200-24,300 slips per acre.
The distances and the number of slips depend on the sweet potato variety, environmental conditions, the irrigation system, and of course, the yield goals of the producer.
(1 hectare = 2,47 acres = 10.000 square meters).
Sweet Potato cultivation guide:
Sweet Potato Soil Requirements, Soil Preparation, and Planting