Agronomic Root Crops

Course CodeBAG310
Fee CodeS2
Duration (approx)100 hours
QualificationStatement of Attainment

Learn to grow root vegetables and other root crops

  • Online learning course
  • Grow better vegetables
  • Apply your learning on the farm, at home or in a community garden

Lesson Structure

There are 10 lessons in this course:

  1. Scope and Nature of Root Cropping and the Botany of Roots
  2. Cultural Practices A: Soil Management, Crop Scheduling and Soil Water
  3. Cultural Practices B: Weed control, Pest Management
  4. Potatoes
  5. Carrots and their Relatives
  6. Turnips and their Relatives
  7. Beets
  8. Taro, Yams and Sweet Potato
  9. Other Root Crops
  10. Harvest and Post-Harvest Management

Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.


Learn to Produce Dozens of Different Types of Root Crops - Enhance the Quality and Quantity

There are root vegetables like potatoes and carrots which have been widely grown around the world for a very long time, others that have been grown mostly in certain regions, and a range of others such as sweet potato which are being grown increasingly across a wider range of regions around the world. 

Growing Sweet Potatoes

Sweet Potato (Ipomoea batatas) can be grown in both tropical or temperate climates, provided conditions are right. Sweet potatoes are a vigorous perennial vine native to tropical America with large, edible tubers.

Growing Conditions for Sweet Potato
Sweet potatoes grow best in warm, dry conditions, with three months of temperatures above 20°C. Shade is needed in very hot conditions. They do not withstand frost.

The ideal soil is a well-drained sandy loam, with a pH in the range of 5.5 to 6.5. Soil must be cultivated to keep the surface loose and free of weeds. Heavy clays can result in roots that are rough and irregular in shape. Excessively light soils tend to produce long thin roots.

Cultivation after planting is minimal. Mechanical cultivation is sometimes carried out after planting, in order to control weeds, until plant growth becomes rapid. Once plants are established, they compete strongly with weeds and further cultivations cease (they would damage the crop once tubers begin forming). 

Nutrient Requirements
Sweet potatoes have an average rate of nutrient uptake - not heavy or light. They need moderate rates of nitrogen, but potassium, phosphorus, calcium and magnesium are needed in higher than normal ratios.  Moderate amounts of nitrogen and higher than normal quantities of potash and phosphorus are required for growth and tuber formation. 

Research has shown that a thick and more even shaped tuber is produced when fed with potash. Tubers grown without potash can be more irregularly shaped. Soils with an excessive amount of nitrogen can produce too much top growth and longer, thinner tubers.
Larger applications of both nitrogen and potash fertilisers may be needed on more freely draining sandy soils. Loams (or any soils that retain nutrients better) should be fertilised less.

If a legume cover crop has been grown and ploughed in before planting, it will have increased nitrogen soil levels, hence less nitrogen fertiliser should be applied.

Most experts recommend against using manures for sweet potato crops; though some growers use low levels of manure.

Planting/Propagation 

  • Propagate from tubers or cuttings. Medium-sized tubers may be planted direct in a bed. Alternatively plant into a box of moist sand in a warm area.
  • When the shoots on the sprouted tubers are 20-25 cm long, transplant them into prepared beds. Plant in rows 1 m apart, with 30-45 cm between each plant.
  • Another way is to strike shoots as cuttings then planted out. This may be more time consuming, but can be a way to reduce risk of disease.
  • Plants are commonly planted 30 to 45 cm apart in rows up to 1 metre apart. Planting may be by hand or machine (for large scale production). Trellising needed.

Problems
Several insect problems including moth grubs, beetles and weevils may be a problem. Fungal diseases that cause rots, leaf spots, rust and fusarium wilt can occur. 

  • Black rot causes dark depressions in the sweet potatoes, and black cankers on underground stems. Crop rotation and use of disease free seed greatly reduces any issue.
  • Internal cork can develop if stored at a high temperature. This involves tuber flesh becoming dry and corky in appearance. Some cultivars are less susceptible.
  • Pox causes soil rot depressions on tubers, thin yellowing leaves and overall stunting of the plant growth. The problem is reduced by improved hygiene, crop rotation and lowering soil pH (adjust pH carefully to 5.2 with sulphur).
  • Stem rot may start as yellowing between veins on the leaf, followed by wilting of vines and deterioration of stems. Hygiene and crop rotation are important to avoid this.

Cultivars
There are hundreds of different forms and cultivars. Sweet potato varieties may be classified in various ways:

  • Feed types – grown for livestock.
  • Food types – varieties grown primarily for humans to eat. These are often divided into soft or dry fleshed varieties.

Dry or firm fleshed types have a firmer flesh after cooking. Soft or moist fleshed varieties have a softer flesh after cooking. These are of greater commercial importance in many countries, including the USA. The soft fleshed cultivars are sold as 'Yams' in the USA, however, these are not actually true yams. 

Drier, harder tubers are usually yellow fleshed. Sweeter, softer watery fleshed tubers may have tubers that are white, yellow, pink, purple or brown.

Harvest
Harvest when the plant is completely yellow and the tubers have a firm skin – normally 3 to 6 months after planting. Store the tubers at 10-12°C in a dark, well-ventilated position, but not in the fridge. 

Uses
Eaten cooked - baked, fried, boiled, as mash, chips or many other ways. Yellow fleshed varieties tend to have a higher nutritional value.

 

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