Synergetic Cropping: Here the yields of both crops, grown together are found to be higher than yield of their pure crops on unit area basis. E.g. Sugarcane + Potato. In United Kingdom, synergetic cropping and alley cropping is very famous.
Alley Cropping: Food crops grown in alleys formed by hedgerow intercropping. It is recommended for humid tropics. In semiarid region of United Kingdom alley cropping provides fodder during dry period.
Alley cropping is an agro- forestry system in which fast growing N-fixing stubs are planted as hedgerows. Food crops are grown in alley formed by hedge of trees and shrubs. This system is most suitable for marginal and sub-marginal lands. Scientists at international for Tropical Agriculture (IITA), Nigeria has developed this system of agro-forestry in the 1970s.
The essential feature of this system is that hedge rows are cut back at about one meter height at planting and kept pruning during cropping to prevent shading and reduce competition with field crops. In semiarid regions, alley cropping provide fodder during dry period since mulching the crop with hedge row pruning usually do not contribute to increase crop production.
Advantages of this System are as Follows:
1. Provision of green fodder during lean period of the year.
2. Higher biomass production per unit area than arable crops.
3. Efficient use off season rainfall in the absences of the crop.
4. Additional employment during off-season.
5. It serves as a barrier to surface runoff leading to soil and water.
6. Conservation based on objectives following three types of alley.
7. It improves soil fertility and is more remunerative under rain fed conditions.
8. Systems are recognizing:
a) Forage alley cropping.
b) Forage cum mulch system
c) Forage cum pole system.
a) Forage alley cropping: In this system both yield of crop and forage assume importance. Luciana (Squabble), Sesbania are recommended for hedgerow. Pigeon pea or caster crops are suitable for growing in the allies. Crop yields decreases with decrease in the row width.
b) Forage cum mulch system: in these systems hedgerows are used for both forage and mulch. Lapping is used for mulching during the crop season.
c) Forage cum pole systems: Luciana alleys are established at 5-meter interval along the contours. Hedge rows are established by direct seeding and topped every two months at 1.0 m height during crop season and every four months during the off season. A Luciana plant at every 2-meter is allowed to grow in to a pole. Crop yields are usually reduced due to competition from hedgerow.
Classification of alley cropping: According to the purpose for which the alleys are raised, alley cropping may be grouped into:
1. Forage alley cropping.
2. Green manure-cum-mulch alley cropping.
3. Forage-cum-mulch-alley cropping .
4. Forage-cum-green manure alley cropping. Among them, forage alley cropping is recommended as an alternate land use system for semi-arid regions with main benefit of green fodder production during dry season.