Outcome 3 - Principles of Vegetable Crop Production

Question 1

What is crop rotation?

Answer 1

A system of cropping whereby you change the crop in any given bed each year, based on which crop was grown in that bed the previous year and the beneficial effects that crop will have had on the soil which will be adventitious to this year’s crop.

Crop rotation is normally carried out on a four year cycle but the longer the cycle the better.

Question 2

What is the order of the crop rotation system?

Answer 2

Year 1. Brassicas

Year 2. Potatoes and others

Year 3. Alliums and roots

Year 4. Legumes.

Question 3

What are the benefits of crop rotation?

Answer 3

• Minimises plant problems
  
  • If crops are grown in same bed each year pests and diseases can build up
  • Nutrient requirements for crops vary and rotating stops specific crops depleting the soil of specific nutrients (soil sickness)
• A crop can benefit from the previous one
  
  • Legumes fix nitrogen, which can be used by brassicas (which require a lot of nitrogen)
  • Potatoes help surpress weeds because of their dense foliage, which can be followed by alliums, which are poor weed surpressors.

Question 4

What are the limitations of crop rotation?

Answer 4

• Difficult to use effectively on a small scale
• In domestic cultivation preferences for particular vegetables sometimes make it impractical to apply
• Pests and diseases are mobile over the smaller areas present in a domestic setting, so rotation can be ineffective
• Some pests and diseases can survive several years in the soil.

Question 5

What is the practical alternative to crop rotation in a domestic setting?

Answer 5

• Avoiding growing the same crop in the same place two years running
• Maintain good soil structure and fertility
• Maintain a pH of 6.5-7
• Observe good garden hygiene.

Question 6

Explain successional sowing.

Answer 6

• Sowing the same variety or cultivar at intervals (different dates, two weeks apart) so that the whole crop does not mature at the same time (e.g. radishes)
• Sowing different varieties of the same crop on the same date. Many crops have early and late varieties (e.g. potatoes)

Question 7

Explain catch crops.

Answer 7

• A quick-maturing crop is planted in an area that will be required later for a main crop
• Plants suitable for intercropping may also be suitable catch crops
• Green manures can be used as a catch crop to enrich the soil and keep it covered.
• e.g. lettuce before cabbages or courgettes.

Question 8

Explain intercropping.

Answer 8

• Growing a quick-maturing crop in the space between slower growing plants (e.g. lettuce between brassicas, or radishes between parsnips)
• The intercrop should not deprive the main crop of water or nutrients and it may be advisable to space the main crop a little further apart.

Question 9

Explain strip cropping.

Answer 9

• Cloches are moved to and fro between two or three strips of adjacent land, so they cover three or four different crops at their critical growth stages to speed up maturity
• e.g. lettuces, carrots.

Question 10

Describe the effect of plant spacing on vegetable crops.

Answer 10

• Ideal spacing will allow a crop to grow uniformly, and allow maximum yield, while allowing ease of management for the grower (these criteria often conflict)
• Size: Closer plantings mean smaller plants (e.g. carrots and onions will be smaller if planted closer together). Wider spacings mean larger plants and sometimes better quality (but can be wasteful of space)
• Soil quality: Close crops deplete water and nutrients quickly so close spacings better suited to beds with better quality soils and water reserves (also, crops grown closer together mature more quickly)
• Weeds: A weedier plot will generally have larger spacings to allow for weed management.
• Pests and diseases. Spread faster in close plantings
• Early varieties can be sown closer together. Main crops require more space because they’re in the soil longer.
• Crops that have high water and nutrient demand should be sown further apart. Crops that require poorer soil require less space.
• Smaller crops, like cylindrical beetroots, need 15cm while globe beetroot need 30cm. Cabbages need 40cm.

Question 11

What is meant by ‘cut and come again’ vegetables?

Answer 11

• Individual leaves or entire lettuce are cut and left to grow again.
• Harvest every three weeks
• e.g. oak-leafed lettuce.