Crop rotation refers to the cultivation of different crops successively, in line with changing seasons. The order and area of crops to be grown is accordingly patterned for optimizing soil nutrients and water, controlling pests and suppressing weeds. Crop rotation in rooftop farming comprises of simple rotation of two or three crops. An easy way by which crop rotation can be integrated in rooftop garden is dividing the garden into different areas and shifting a crop species from one area to another. It can also be exercised by rotating crops of different families or groups in a particular area. Crop families or groups that can be rotated are as following:
Alliums: Onion, Garlic, etc.,
Brassicas: Kale, Cabbage, Broccoli, Cauliflower, Radish, Carrot, etc.,
Cucurbits: Bitter gourd, Pumpkins, Chayote Squash, Cucumbers, Sponge gourd, etc.,
Nightshades: Brinjal, Peppers, Potatoes, Tomatoes, etc.,
Leguminous vegetables: Beans, peas, chickpea, etc.,
Leafy vegetables: Mustard, Basmati mustard, Green cress, spinach, coriander and lettuce, etc.
Principles of crop rotation
An effective crop rotation system requires right selection of crops that adjusts well with the space, sunlight and soil in rooftop garden. General principles that guide crop rotation are listed hereafter:
- Leguminous crops should be followed by non-leguminous crops.
- The crops with tap roots (dicots) should be grown after those which have fibrous root system (monocots).
- Slow-growing crops which are more vulnerable to weeds should be grown immediately after weed-suppressing crops in a rotation system.
- Closely related species should not be grown successively as they act as alternate hosts for insects, pests and diseases.
- Deep rooted crops should be succeeded by shallow rooted crops.
- Crops susceptible to soil borne pathogens and parasitic weeds should be followed by tolerant crops.
- Diversely classified families and groups should be incorporated in the rotation.
Advantages of crop rotation
The advantages of integrating crop rotation system in rooftop farming are illustrated below:
- Crop rotation furnishes soil with fertility. The root nodules of leguminous crops fix atmospheric nitrogen into the soil and supply nitrogen for subsequent non-leguminous crops. Similarly, deep-rooted plants can uptake phosphorus and potassium from depth of the soil profile making the nutrients accessible to shallow rooted crops following.
- Pests are specific to certain host species or families by nature. Growing non-host species in succession can control reproduction, growth and development of those insects having small range of crops to feed on which are immobile, whose larvae or eggs overwinter in the soil or crop residue.
- Including cover crops in the rotation limits necessities of light, space and nutrient for weeds. Consequently, the weed population is suppressed.
- Pathogens having small host range which need crop residue for survival during off-season can be controlled by cultivating non-host plants. This helps to cease the reproduction process of pathogen hence checking the spread of disease.
- Crop rotation enhances soil organic matter adding up more crop residues and green manure to the soil.
- It promotes crop diversity as well as microbial activity causing minimal disturbance to the soil.
- It favors optimum utilization of space which is prominent in rooftop farming.