How to inoculate Inga seeds prior to planting

Inga edulis seeds freshly shelled from their pod. Inga  seeds are viviparous, that is they germinate directly without passing through a dormant or quiescent phase as in the case of most seeds

We are using Inga to restore soils to productivity because of its ability to grow rapidly in, and improve the fertility of compacted, acidic and nutrient poor soils.  This is depends on its ability to form an association with  Rhizobia bacteria in the soil which, in return for shelter and some sugar, convert nitrogen in the air to a form which promotes plant growth in the soil. This association takes the form of small nodules on the roots (see image below) which act as mega bacteria colonies. If our seedlings are to restore soils to productivity then it is essential that we help them form these associations. In the pod the seeds are not in contact with Rhizobia bacteria and in the wild inoculation would occur only when the seed falls to the ground and comes into contact with the soil.

An Inga edulis root nodule. The nodule is an association between root cells and Rhizobium bacteria. The root provides sugar, the bacteria provides nitrates which are  essential for plant growth

We inoculate the seeds by soaking them over-night in a mixture of macerated Inga root nodules and soil suspended in water.  We obtain the roots by digging around the base of an Inga tree and looking for nodule-bearing roots.To macerate the roots we rub them vigorously against themselves in water as you would do hand-washing clothes. Leave the soil that came attached to the roots on as this should also contain Rhizobia. The idea is to rupture the nodules and create a solution rich in bacteria so that when you add the seeds they are quickly colonised.

Inoculating seeds involves soaking them overnight in a solution of macerated nodule-bearing roots. Nodule-bearing roots can be easily found by digging around the base of an Inga tree. Click on image to view clip of macerating roots.

Once planted in bags we water the seeds with the liquid that is left over, hopefully ensuring that the soil is also inoculated. It is very important that the seedlings have the best possible chance of being inoculated. Below you can see a four-month old seedling prepared as described above. The small white nodules are clearly visible.

An Inga seedling at four months of age with nodules clearly visible. The seed was soaked overnight in macerated Inga roots

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