Inga alley cropping was developed as an effective, sustainable alternative to slash and burn agriculture in the rainforests and former rainforest lands. Here the soils are frequently degraded and acidic and Inga has good tolerance for such soils. Not all the Inga species are suitable. Caution needs to be exercised in parts of the world where the Inga tree is not native, but it has now been used widely in many countries without serious problems.
It takes between 8 months and two years (sometimes even more if the plot has been neglected or there has been a drought) to get Inga alleys established. The exact length of time will depend on how much sun and rainfall there is, the soil, and the care the farmer takes of the young trees. However, the yields are good. Compared to reusing previously cultivated plots, harvests can be as much as 15 times higher with Inga than without it. Costs are minimal. And of course the same plot can be used over and over. We know of plots that are now over a decade old and still providing yields as high or higher than at the start, as mulch builds up. Some farmers have noted that the harvest is better than even the first year they get on a fresh plot after burning primary rainforest. (We are in the process of gathering more quantitative data on this.)
There have been over two decades of meticulous research followed by field trials1,2. The farmers who have taken it up have been able to stay on the same plot for many years and are very happy with it. At the end of the first field trials the plots had lasted six years with just one initial application of rock phosphate. They have continued since. The Inga recycles what the crops do not use. It also has mycorrhizae (fungi) in its roots which supply phosphorus. Even if, as the original researcher thought, some further rock phosphate would eventually be needed, it is expected that this would ensure a long fertile period and be very affordable for the farmers.
Since then however we have had many successful plots, particularly in Ecuador and Cameroon, some of which are over 10 years old, with no rock phosphate needed in either country. We therefore recommend that the system be tried without any such addition, and the rock phosphate be used only when if becomes apparent that it is really necessary.
Yes, very much. The strongest proof of that is that after trying it on a small scale they typically want to expand their Inga plantings.
What is harder is to convince farmers to start it for the first time. They usually need to see it in operation in a demonstration plot. However, after a field worker from Guatemala had visited the Inga demo facility at CURLA and described and illustrated his visit with photographs of the Inga alleys, he reported that over 5,000 families in the Maya heartland wished to try it. Nonetheless we have seen the most success by showing farmers demo farms.
Moreover Inga is not a quick fix. From sowing the Inga seed to pruning and sowing the first crop can take up to two years if the soil is poor and the plots are not weeded. If the conditions are very poor it can even be three years, though in very favourable conditions 8 months has sufficed. During that time the farmers are likely to need support e.g reassurance that it will work, technical advice, and financial help such as some form of micro credit until they get the benefits of the first crop. They will also need seed and bags to grow the seed in, and may need fencing to protect the field, and possibly rock phosphate to start off the system. Sometimes however the seeds have been planted successfully in the ground straight away, or nurseries using this bare root method have been used. These two methods save on costs and inevitable litter. While the Inga is small low crops can be grown in the alley, but not crops that would shade the young trees and so slow their growth. Possibly the farmer would only start with a small plot but expand later.
The system has appealed particularly to farmers who have had to farm in the most difficult conditions, like on acid soil or on steep slopes. Inga alley cropping has been effective in preventing or reducing soil erosion on hillsides, even in very adverse weather conditions. This is clearly of great benefit to such marginalised farmers. It has also been very useful in reclaiming previously degraded barren land.
At a maximum they may need seed and bags to grow the seed in, fencing to protect the field, rock phosphate to start off the system and tools for planting and pruning. But, as stated above, we are not using rock phosphate in Ecuador or Cameroon, and seeds sown directly into the ground have also grown well.
One problem with adopting this system is the delay of usually about two years before the Inga plot becomes productive, although it may be possible to grow beans sooner if the soil and climate are favourable. Also valuable firewood is obtained long before the first proper harvest.
Initially getting the system under way takes hard work, but once the Inga is well established the farmer saves time and energy. In the first year, to establish the system, the farmer has to pre-slash the site to keep down the weeds, then plant the Inga, and then slash the weeds again round the young trees till they are fully established. There needs to be a clear area of about a metre round the base of each tree. 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 be put under Inga alley cropping in later years.
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 as there is very little weeding to be done. Moreover for slash and burn there is often additional time, which can be as much as 2 or 3 hours a day, in walking to the latest cleared plot. The alleys, can be permanently sited next the farmer’s home thus saving this time.
The trees are pruned before they flower. So if it is intended to produce Inga seed, for example to increase the area planted as Inga alleys later, or to supply neighbouring farmers with seed, a tree needs to be left unpruned, maybe at the end of a row. Funders might stipulate that in return for seed, etc. the farmer grows one such tree to supply the neighbours with seeds later when they have seen how well the system works.