Rainforest Saver SCIO, SC 050373
In this section we share practical advice for farmers gained from research and our experience working with Inga allies.
Inga alley cropping is suitable for use in both rainforest and former rainforest lands, including degraded and acid ones. It requires a good rainfall, 1200 mm or more. It can be grown at elevations of up to 1600 m. While the Inga tree may grow at greater heights it does not typically grow well enough to allow alley cropping so we cannot recommend using it at elevations over 1600 m.
We recommend Inga edulis or Inga oerstediana as these have proved the most reliable. The most commonly used species is Inga edulis.
Several species of Inga have been tested and further research is being carried out so these conclusions may change in future.
Of the other species of Inga, only vera has performed reasonably well in some conditions. However it does not appear to be as reliable as edulis or oerstediana. Inga nobilis, jinicuil cocleensis and punctata are not recommended, and some trials with Inga marginata and samanensis have also not done well2
Inga edulis trees. Photo by Gaston Bityo
The following inputs are needed:
* In the original research, it was thought that rock phosphate could make a big difference starting off the system on very degraded soil. In reality we have not found it necessary. In both Cameroon or Ecuador the crops have done very well without it. If you do need it, as a rough guide, in past trials one $8 bag of rock phosphate has been sufficient for a hectare of land.
While we list plastic bags, we are experimenting with bare root nurseries to see if we can avoid using them to save expense and waste.
We have had good results from planting the seeds directly in the ground where the Inga is to grow. Germination is generally good (but see the next section below) so one should not need many extra seeds at the start.
Inga edulis produces seed from about three years old, but sometimes sooner. One large Inga tree can produce about 1000 seeds. So planting a hectare of land would require harvesting seeds from around 5 trees. Or one tree might supply 2 to 4 farmers with enough seed to plant a 1/10th hectare plot each. In Cameroon we have started many farmers off with much smaller plots, sometimes even with as few as 50 Inga trees. That is enough to demonstrate to them that the system works.
Collecting Inga pods. Photo Pastor Nsandah, Kenya.
For the first year, the farmer needs to put in a lot of work. He has to pre-slash the site to keep down the weeds, plant the Inga, and 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 around 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 good results.
From the second year on the alley cropping system requires very much less work than slash and burn, about half the man hoursa. And as the alley produces crops for many years the farmer saves a very considerable amount of time over the lifetime of the plot.
It is important to harvest the seed pods quickly once they are ready. The pods will go bad if they are left on the tree too long, or they may get eaten by animals. If you are intending to harvest seeds watch your Inga tree carefully so you can do so as soon as it is ready.
Once the seeds are collected they have to be removed from the pods and cleaned of the ‘fluff’ to prevent them going bad or mouldy. They should be kept moist until planted, for example in a bucket of water. To ensure the formation of root nodules and the successful start of the mycorrhizal fungi, the seeds should be soaked in water with broken up pieces of root nodules and soil taken from a mature Inga tree for twelve hours.
Once harvested, they do not remain viable for long. It is best to plant them within 5 days – or two weeks at the outside.
Podding Inga seeds, Cameroon. Photo by Linus
Inga seeds in a bucket of water. Photo by Antony Melville.
To create a seedling nursery, plant the seeds into compost. Local forest soil containing organic matter is very suitable. Use black plastic bags and plant not more than 2 cm below the surface. Usually, one seed is planted per bag, but if there are plenty of seeds two may be sown and later the smaller one removed. Grow them in partial shade until they are ready to be planted out. This is typically 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, Ecuador.
Inga seeds can also be planted straight into the soil. We have seen varying levels of success doing this and so planting in a nursery initially is our usual recommendation.
Planting out Inga seedlings. Photo Linus.
It is best to plan to do the planting out when there is likely to be some cloud cover and a reasonable amount of rain. We have seen mixed results when planting at times with lower rainfall. For example 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 well. We have seen better results planting in May/June in Honduras when there is less exposure.
Another consideration is that birds (particularly parrots) love the seeds. In Honduras, there is less seed loss to birds in April than in October/November when fewer alternative foods are around for the birds.
Ensure the ground area is cleared of weeds before planting. You can do this by slashing the plot to fully clear the plot.
A poorly grown seedling planted out in January with little rain, photo was taken in April. Honduras. Photo by Antony Melville.
It is critical that the plot is regularly weeded in the early stages. This is to allow the seedlings to grow. Once they are large enough the trees will keep the weeds down themselves. When they eventually close their canopies across the alleys they suppress the weeds very effectively by shading, shedding leaves and then by the mulch formed when they are pruned.
Row on young Inga following the contours of the land. Photo by FUPNAPIB .
Plant your Inga seedlings in rows, like hedgerows with alleys in between. A distance of half a metre may be left between adjacent plants and a distance of perhaps 4m left as the alley width (the distance between the rows). This can be varied a little, 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, 4m has been generally used.
On hillsides, plant Inga along the contours. Pruned branches can be laid across the stems to stop erosion. Inga alleys have been found to be effective in preventing erosion. Otherwise, the alleys can be aligned so as to minimise the shading of crops by the trees, that is, taking account of the direction of the sun.
Rows of young Inga planted out following the contours. Photo by Chanchamaya project, University of La Molina, Peru
Pruned stems laid across the rows of Inga to prevent erosion. Photo by Marco
The time to prune the trees for the first time is when they have closed their canopies. This is generally about two years after first planting. At this stage they will have shut out the light in the alleys and thus killed most of the weeds. In good conditions, this may take a little less than two years but if 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, and the weeds have been suppressed in the alley. Photo Tiiu Miller
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 is about 1m and a maximum height is 1.75m. Obviously, the higher the pruning the quicker the regrowth. 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 sharp tool a little way above a node, at an angle to allow rainwater to drain off.
Natalie pruning the Inga. Ecuador.
Rapid growth, particularly before the first pruning, or later if the pruning is infrequent, can result in there being little foliage lower down on the trees. The result of this is that if the Inga is pruned down to the usual height, bare stems with neither leaves nor leaf nodes would be left. This makes regrowth slow, and even risks killing some of the trees. So a two-stage pruning is better. There are two ways to approach this. In one method in the first stage, the central stem is cut out to encourage branching from lower down, so that when the second pruning is done there are some leaves low enough to be left on the stem after the pruning. However this will only be successful if enough light reaches the lower stem for it to grow branches. Failing this, you 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.
The exact timing of pruning will depend not only on when the canopies have closed but when the crops need to be sown. A first pruning might be done 4 to 6 weeks before planting time, and a second, if needed, two weeks before 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 however the pruning is done, it is important not to totally remove the foliage from the trees. The Inga trees can withstand a lot but will not withstand the total removal of their foliage.
Larger branches, which are particularly plentiful on the first pruning, make good firewood. However you must ensure that 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 subsequent years the mulch in the lower layers will rot. This provides nutrients for the crops to feed on, while the newer prunings 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.
Crops are planted into holes that you make in the mulch. Maize and beans have big seeds that are strong enough to then grow up through the mulch. Smaller weeds cannot manage to grow.
Maize, beans, vanilla, pepper, and pineapples are examples of crops that have been successfully grown in Inga alleys. As the farmer can reclaim degraded land next to his home and use it year after year, you can keep an eye on valuable cash crops, and your family can help to maintain the plot.
Vanilla and pepper can be grown on living support such as Gliricidia sepium in the middle of the alleys.
Pepper planted out and thriving on a living support in an Inga alley. Photo by FUPNAPIB.
When the crops have been harvested the Inga is allowed to regrow until it has closed the canopy again and the cycle can be repeated over and over.
Pineapples thriving in an Inga alley. Note the Inga regrowing on either side. Photo by FUPNAPIB 2006.
References and Further Reading
E.C.M. The Genus Inga: Utilization. The Royal Botanic Gardens, Kew, 1998.
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
9. Pennington, T. Inga Management. In Pennington, T.D. & Fernades, E.C.M. The Genus Inga: Utilization. The Royal Botanic Gardens, Kew, 1998. 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 to what uses the Inga has been put.