Advice for farmers

Practical notes on how to do Inga alley cropping

               SUBSECTIONS

What kind of environment is suitable?

Which species of Inga are suitable?

What inputs are needed?

Seed collection, viability and planting the seeds

Planting out

Pruning

Planting the crops

After the Harvest

References and Further Reading

 

What kind of environment is suitable?

Inga alley cropping is an effective, sustainable alternative to slash and burn agriculture in rainforest and degraded former rainforest acid soils of Central and South America It requires a fair bit of rainfall, 1200 mm on more, and it can be grown at elevations of up to 1600 m. 

However it could be practiced anywhere where suitable species of Inga can be grown.

Which species of Inga are suitable?

Several species of Inga have been tried.  The conclusions should not be regarded as final: other species may be found that perform well, and local variation may be important too, and there may be an advantage in trying a local species that is known to thrive in the region.  But after a substantial amount of practical investigations Inga edulis and Inga oerstediana have proved to be the most reliable. The most commonly used species is Inga edulis. Inga vera has sometimes performed well too, but not always.

Inga vera tree

Inga vera tree. Photo by Antony Melville 2007.

Inga nobilis, jinicuil and cocleensis and punctata are not recommended, and some trials with Inga marginata and samanensis have also not done well.

What inputs are needed?

Inga seed, black plastic bags and soil or compost to grow the seed in before it is ready for planting out, fencing, and tools, including a good sharp one for pruning the Inga. Mycorrhizal inoculum may be required, and an initial application of rock phosphate can make a big difference to start off the system on degraded soil.  As a rough guide, in past trials one $8 bag of rock phosphate has been sufficient for a hectare of land. A hectare of land requires 5000 Inga trees. Germination is generally good (but see the next section below) so one should not need many extra seeds to begin with.

Inga edulis produces seed from about three years oldOne large Inga tree produces about 1000 seed, maybe more. So planting a hectare of land would require 3 to 5 trees.  Or one tree might supply 2 to 4 farmers with enough seed to plant a 1/10th hectare plot each.

Collecting Inga pods

Collecting Inga pods. Photo by Antony Melville 2007.

For the first year the farmer would need to put in a lot of work. He has to preslash the site to keep down the weeds, then to plant the Inga, and then to slash the weeds again to keep an area of about a metre diameter clear round the base of each tree till the young trees are fully established at about six months. This might come to over 100 man-days for a hectare.  However most farmers would want to start much smaller than that, for example with a tenth of a hectare, and this would make the work quite manageable.  More land could then be put under Inga in subsequent years when the farmer has seen the good results.

However from the second year on the alley cropping system requires very much less work than slash and burn, about only half the man hours.  And as the alley produces for many years the farmer saves a considerable amount of time.

Seed collection, viability and planting the seeds

The pods go bad if left on the tree for too long, or they get eaten by animals, and do not remain viable for any length of time after collection either - two weeks at the outside, but it is best to plant them within a week.   For example when seeds were collected on Monday and podded into a bucket of water on Tuesday, many were putting out roots before they went into the ground on Thursday.

Podding Inga seeds

Podding Inga seeds. Photo by FUPNAPIB 2006.

So while seeds have been successfully transported from a nursery to a plantation over many miles (and as long as 5 days) generally one wants to have a tree with ripe fruit reasonably close. and once the tree has been found one has to keep a watch on it to be sure to be ready to collect the seed as soon as it is ready. Once the seeds are collected they have to be removed from the pods, cleaned of the 'fluff', and kept moist until planted, for example in a bucket of water.

Inga seeds in a bucket of water

Inga seeds in a bucket of water. Photo by Antony Melville 2007.

To ensure the formation of root nodules and infection with the mycorrhizal fungi the seeds can be soaked in water with broken up pieces of root nodules and soil taken from a mature Igga tree for twelve hours.

They are planted into soil or compost, local forest soil containing organic matter being very suitable, in black plastic bags not more than 2 cm below the surface. Usually one seed is planted per bag, but if one has plenty of seeds two may be sown and later the smaller one removed. They are grown in partial shade until they are ready to be planted out two to three months later when they have grown to a height of 30 to 40 cm. The shade should be progressively reduced and removed prior to transplanting. They need plenty of water both as seedlings in the nursery and when planted out.

Seedling nursery

Seedling nursery. Photo by FUPNAPIB 2006.

Whereas Inga seeds can also be planted straight out into the soil this has been less successful. Planting initially in a nursery is recommended.

Planting out

Planting out Inga seedlings

Planting out Inga seedlings. Photo by FUPNAPIB 2006.

Before planting out the seedlings the farmer has to slash the weeds to clear the ground for them.

It is best to plant out the seedlings when they are likely to get some cloud cover and a reasonable amount of rain, so local climate conditions should be considered. Some January plantings in Honduras when the rainfall was low and there was little cloud cover to shield the young plants from the hot sun did not do at all well. Had they been planted in May/June they would have had less exposure. In Honduras there is less seed loss to birds in April than in October/November when fewer alternative foods are around for the birds. Parrots love the seed.

Poorly grown seedling

Poorly grown seedling, planted out in January with little rain, photo taken in April. Photo by Antony Melville 2007.

Until the trees are established the weeds around them need to be kept down by slashing, but once they are big enough they hold their own against the weeds, and when they eventually close their canopies across the alleys they suppress the weeds very effectively by shading, shedding leaves and the mulch formed when they are pruned.

Row on young Inga following the contours

Row on young Inga following the contours of the land. Photo by FUPNAPIB 2006.

The young Inga is planted out in rows, like hedgerows with alleys in between.  A distance of perhaps half a metre might be left between adjacent plants and a distance of 4m as the alley width, that is, the distance between the rows, but this can be varied.  The wider the alley the less competition there will be between the trees and the crops, but if the alley is too wide the trees may not provide enough shade and mulch to cover the alley and smother the weeds.  The best alley cropping trees, Inga edulis and Inga oerstediana can probably function with an alley width of 5m. However, 4 have been generally used.

On hillsides the Inga are planted along the contours, and pruned branches can be laid across the stems to stop erosion.  Such Inga alleys have been found to be resistant to erosion.  Otherwise the alleys might be aligned so as to minimise the shading of the crops by the trees, that is, taking account of the direction of the sun.

Rows of young Inga planted out following the contours

Rows of young Inga planted out following the contours. Photo by Chanchamaya project, University of La Molina, Peru 2006.

Pruning

The time to prune the trees is when they have closed their canopies, generally in about two years, so that they have shut out the light in the alleys and thus killed most if not all of the weeds. In good conditions this may take even less than two years but if the conditions are not good, for example there is insufficient rain or the soil is exceptionally poor, three years may be required.

The canopies have closed over

The canopies have closed over, and the weeds have been suppressed in the alley.

Photo by FUPNAPIB 2006.

How the pruning is done is very important.  If they are pruned too low down the trees are apt to die.  One should not remove absolutely all the foliage. The minimum height for pruning might be about 1m and a maximum height of 1.75m. Obviously the higher the trees are pruned the quicker they will regrow.  Lower pruning will let in more light and there will be less competition from the trees to the crops.  Pruning should be done with a clean, careful cut with a good sharp tool a little way above a node, at an angle to allow rainwater to drain off and far enough from the main stem to avoid the risk of damaging it.

Pruning the Inga

Pruning the Inga. Photo by FUPNAPIB 2006.

Rapid growth, particularly before the first pruning, or later if the pruning is infrequent, can result in there being little foliage low down. This means that if they are then pruned down to the right height bare stems with neither leaves nor leaf nodes would be left.  This would make regrowth slow, or even kill the trees.  So a two-stage pruning may be better.  There are two ways to do this. In one method in the first stage one can cut out the central stem to encourage branching from lower down, so that when one does the second pruning there are some leaves low enough to be left on the stem after the pruning.  However, this may not be successful. If enough light does not reach the lower stem it may not grow branches. In that case one can cut out all the side branches higher up and leave the main stem. This will encourage more branching lower down, and when that has happened the central stem can be pruned

Recently pruned row of Inga

Recently pruned row of Inga. Photo by FUPNAPIB 2006.

The exact timing of the pruning will depend not only on when the canopies have closed but when the crops need to be sown.  The first pruning might be done 4 to 6 weeks before planting time, and the second pruning within a fortnight of planting.

If the trees are growing too vigorously and competing with the crops some light pruning can be carried out as needed while the crops are growing. But whatever way the pruning is done it is important not to totally remove the foliage.  The Inga trees can withstand a lot but not the total removal of all the foliage.

Larger branches, which are particularly plentiful on the first pruning, make good firewood.  The smaller twigs and the leaves are however left to lie in the alleys to form mulch.  The thick leaves of the Inga form a protective layer over the soil, essential in the hot sun, which would otherwise dry out the soil and the roots of the crops. In succeeding years the mulch in the lower layers rots down for the crops to feed on, while the newest prunisgs form a protective layer on top. When the trees are pruned less often there is more woody growth and so more firewood, but also more competition from the trees with the crops.

On hillsides some branches are laid across the Inga stems to prevent erosion.  The Inga system has been found to be very resistant to erosion.

Prenenting erosion

Pruned stems laid across the rows if Inga to prevent erosion. Photo by FUPNAPIB 2006.

Planting the crops

The crops are planted into holes the farmer makes into the mulch. Maize and beans have big seeds that are strong enough to then grow up through the mulch, whereas the smaller weed seeds cannot manage that.

Maize, beans, vanilla, pepper, and pineapples are examples of crops that have been successfully grown in the Inga alleys.  As the farmer can reclaim degraded land next his home and use it year after year he can keep an eye on his expensive cash crops, and his family can help. 

Vanilla and pepper can be grown on living supports such as Gliricidia sepium in the middle of the alleys. 

Growing pepper (All photos by FUPNAPIB 2006):

Pepper seedlings

 

Pepper seedlings

 

Covering the seedlings

 

Covering the seedlings

 

Pepper planted out in an Inga alley

Pepper planted out and thriving on a living support in an Inga alley. Photo by FUPNAPIB 2006.

After the Harvest

When the crops have been harvested the Inga is allowed to regrow until it has again closed the canopy and the cycle can be repeated over and over.

 

Pineapples in Inga alley

Pineapples thriving in an Inga alley. Note the Inga regrowing on either side. Photo by FUPNAPIB 2006.

This section is based on the following references, with the intention of giving a readable summary of the research to date

 

References and Further Reading

1. An excellent account of alley cropping with some reference to Inga, but not an account of the specific technique of Inga alley cropping being promoted by Rainforest Saver.

Fernandes, E.C.M. International Agroforestry Resourcesdefinition of alley-cropping http://www.css.cornell.edu/ecf3/Web/new/AF/alleyCrop_02.html 2003.       

2. Hands, M.R.  The uses of Inga in the acid soils of the rainforest Zone: alley-cropping sustainability and soil-regeneration. In Pennington, T.D. & Fernades, E.C.M. The Genus Inga: Utilization. The Royal Botanic Gardens, Kew, 1998.

3. Hands, M.R. Alley-cropping as a sustainable alternative to shifting cultivation:  phase III. Inception report. Commission of the European Communities directorate general 1.   North-South relations.   Tropical forests budgetary line project HND// B7‑6201 / IB / 97 / 0533(08) May 1998

4. Hands, M.R. Alley cropping as a sustainable alternative to shifting cultivation:  Phase III Final Report . Commission of the European Communities directorate general 1.   North-South relations.   Tropical forests budgetary line project HND// B7‑6201 / IB / 97 / 0533(08) June 2002.

5. Hands, M.R.  Presentation given at Kew.   September 2005.

6. Hands, M.R.   The uses of Inga species.  Unpublished manuscript c.2003

7. Hands, M.R.   The Inga project 2005 and onwards. c. 2005

8. León Geldres, Jaime The Chanchamaya  Project. News Archives this site.

9.    A very good account of how to grow it, descriptions of the tree and its habitat, and of uses and problems encountered in growing it, with several further references. Recommended as additional reading

Lawrence, A.   NFT highlights:  a quick guide to nitrogen fixing  trees from around the World. http://www.winrock.org/fnrm/factnet/factpub/FACTSH/inga.htm Forest, farm and community tree network, 1993.

10. Melville, A. Some thoughts on expanding the use of Inga alley cropping News Archives this site.

11. An excellent account of Inga management, covering pretty well what one would want to know when one was planning on using the system: very useful tips on topics like seed collecting and preservation, other means of propagation, sowing, transplanting, species selection and even te what uses the Inga has been put.

Pennington, T.  Inga Management  . In Pennington, T.D. & Fernades, E.C.M. The Genus Inga: Utilization. The Royal Botanic Gardens, Kew, 1998.

12. World Agroforestry Centre.   A tree species reference and selection guide    http://www.worldagroforestrycentre.org/sea/products/afdbases/af/asp/SpeciesInfo.asp?SpID=991   International Centre for Research in Agroforestry,  2004.