Alley Cropping with
Nitrogen Fixing Hedgerows
L. Robert Barber, & Ilene Iriarte
Guam Cooperative Extension Service & Guam Department of
Funding provided by:
United States Department of Agriculture Natural Resources
Conservation Service, Western Region Sustainable Agriculture
Research and Education, Administration for Native Americans,,
& Sanctuary Incorporated
What are Nitrogen Fixing Trees
• Trees & shrubs that have the ability to
“fix” or take Nitrogen (N₂) from the air &
use it for growth through a symbiotic
relationship with bacteria called Rhizobia
– Nitrogen is often a limiting nutrient for plant
growth, mulch from NFT provides nitrogen.
– Rhizobia in root nodules fix the nitrogen.
– May need to inoculate the planting medium.
What are Rhizobia?
• Bacteria, which are normally free-living in the
soil in the native range of a particular legume
• They infect (inoculate) the root hairs of the plant
and are housed in small root structures called
• They live in symbiosis with the plant. The plant
provides energy to feed the bacteria & fuel the
nitrogen fixing process & in return the plant
receives nitrogen for growth
• There are thousands of strains of Rhizobia, &
they need to be matched up with the proper
species of NFT to be effective
Benefits of Using NFT’s
• Synthetic fertilizers are:
– Can be detrimental to soil microorganisms
– Pollute ground water due to: too much
applied & rapid leaching
• Nitrogen Fixing Trees:
– Restores natural fertility process
– Onsite resource for nitrogen fertilizer
– Provide organic matter as mulch
NFT Hedgerows in Alley Cropping
• Alley cropping:
– Space between the NFT hedgerows where
crops are grown are called “alleys”
• NFT hedgerows are managed to be readily
available to provide on-site organic matter
• NFT hedgerows are cut back periodically
& the trimmings are applied to the crops
NFT Hedgerows in an Orchard
• Fertilizing effect of mulch is maximized by
mulching around the target trees:
– Nutrients are concentrated on the crop rather than
spreading it over a large area like annual crops
• Minimized competition for nutrients, light, &
water between orchards and hedgerows
• Physical distance between crop trees &
hedgerows can be significantly greater than
NFT for Sloping Land
• On sloping land, the hedgerows are
planted on the contour creating “contour
hedgerows”, or contour vegetative
• Helps control erosion
– May plant NFT closer together than on non-
– Recommended spacing in row is 1 to 1.5 feet
between NFT plants.
Soil erosion after heavy rainfall leads to serious problems in coral reef ecosystems.
Image courtesy of the Guam Forestry and Soil Resources Division, Department of
Contour Hedgerow Planning
• Determine the needs & goals for your project
• Determine the appropriate hedgerow species for
your needs, goals, & site considerations
• Determine appropriate spacing between
– Slope of land a key factor in row spacing, the steeper
the slope the closer the hedgerows.
• Determine appropriate spacing within
hedgerows (between NFT’s), 1’ to 1.5’ average.
• Determine position & spacing of crop trees
Factors to Consider in Species
• The goal is to put the right tree in the right place
– Do you have NFTs present already? (Tangantangan)
• Environmental tolerances should be the most
important concern (rainfall, soil, pH etc.)
• Growth Rate:
– Do you want a highly productive species, or one with
• Generally want high growth rate coupled with a tolerance
for regular coppicing, be careful not to introduce an invasive
– How many times do you want to prune?
• Gliricidia sepium is popular for northern Guam.
Row of Gliricidia sepium
Factors to Consider in Species
– Can you manage a potentially weedy species?
– Do you have weed species that you can bring under
control ( Leucaena sp Tangantangan).
• Other Products:
– In the future would you want to use the NFT’s for
animal fodder, or firewood?
• Other Functions:
– Does your site have a need for wind protection or
• Weed control is essential during establishment
– If properly mulched weeds should not be a problem
– Stay on top of weed growth on the edges of the
• Seedlings may be lost to predators such as slugs,
– Avoid gaps in hedgerows, lost seedlings should be
planted right away
– If not growing seedlings in shade of older hedgerows
will be difficult
First Pruning of Hedgerows
• First pruning should take place after the trees are well
• Best during a period of rapid growth (rainy season)
• It may take up to 6-12 months before trees can be first
• First time the hedges are cut there will be a considerable
amount of wood stem harvested.
• Generally plants should be pruned no lower than 1.5 feet
high (maybe even 3 feet for some species).
• The wood is normally laid at the base of the hedges to
help with erosion control or it can be feed into a
Ongoing Mulching Process
• Successive pruning's should occur when stems
are still soft and leafy
– Normally every 3-6 months
– Depends on species of NFT’s, rainfall, & other factors
• Simply add the fresh mulch on top of the older
Time to plant some NFTs