Alley Cropping with Nitrogen Fixing Hedgerows

Prepared by: L. Robert Barber, & Ilene Iriarte

For: Guam Cooperative Extension Service & Guam

Department of AgricultureFunding 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 (NFT) ?

• 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 nodules

• 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:– Costly– 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

Hedgerow Alley

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 annual crops

NFT for Sloping Land

• On sloping land, the hedgerows are planted on the contour creating “contour hedgerows”, or contour vegetative barriers.

• Helps control erosion– May plant NFT closer together than on

non-sloping land.– 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 Agriculture.  

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

hedgerows – 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 Selection

• 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 less vigor?• Generally want high growth rate coupled with a tolerance

for regular coppicing, be careful not to introduce an invasive species.

– How many times do you want to prune?• Gliricidia sepium is popular for northern

Guam.

Row of Gliricidia sepium

Factors to Consider in Species Selection

• Weediness:– 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 erosion control?

Early Maintenance

• Weed control is essential during establishment of hedgerows– If properly mulched weeds should not be a

problem– Stay on top of weed growth on the edges of

the prepared area

• Seedlings may be lost to predators such as slugs, or chickens– 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 established.

• Best during a period of rapid growth (rainy season)

• It may take up to 6-12 months before trees can be first cut back.

• 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 chipper/shredder

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 mulch.

Time to plant some NFTs