Promoting Musangu (Faidherbia albida) Cultivation: Some Thorny Issues

Notes on Agriculture in Zambia no 4: Promoting the cultivation of the tree Faidherbia albida (winterthorn, musangu) successfully requires more attention to (a) presence of favourable growing conditions; and (b) to social issues pertaining to rights over planted trees and land use in traditional farming area's (i.e., "tribal land").

Initiated: 25 September 2011
Updated: 22 Oct 2012, 29 January 2014, 9 March 2015

The Musangu features with the Jatropha in the Conservation Agriculture scheme of the Conservation Farming Unit (CFU) of the Zambia National Farmers Union (ZNFU) as one of the two non-food trees and is the more prominent of the two for reasons stated below. The CFU mentions the tree in its conservation farming handbook (ZNFU 2007 : 47) and provides on the Internet a very useful, more detailed information sheet (go to: www.aec.msu.edu) that provides the rationale of musangu promotion.

I need to state, at the onset, that I am not a trained agriculturalist. We farm at an 8 ha plot outside of Choma, Southern Province, on land with low natural fertility. My interest in musangu springs directly from this adverse condition.

Well developed 2.5 year old musangu in Choma district. About 150 cm tall.

Some basics about the tree

The musangu, the chiTonga name of the tree, is indigenous to some parts of Zambia. It occurs, for example, naturally in the Gwembe Valley. The English common name for the tree is Winterthorn, referring to its highly unpleasant thorns. The tree, requiring decades to achieve full maturity, grows a wide, impressive canopy and secures its water requirements by a deep tap root. CFU propagates the leguminous tree mostly because of its soil fertilising capacity. I quote out of the handbook:

Through leaf and pod fall, nitrogen fixation and association with soil-micro-organisms, fertility accumulation under the canopy is reported as follows: 75 kg N, 27 kg P2O5, 183 kg CaO, 39 kg MgO and 20 kg S. This is equivalent to 300 kg of complete fertiliser and 250 kg of lime worth at least USD 330 today and provides the recommended nutrient requirement for a 4 ton maize crop.

Wikipedia’s musangu page also mentions: the use of the wood as fire wood and for carved objects like canoes and pestles; medical properties of the tree; use of seed pods as animal food and its importance for bees as an out of season food source.

The tree is in listed in Appendix A (Plants used by the Gwembe Valley Tonga of the Middle River region) of Thayer Scudder's The Ecology of the Gwembe Tonga (1974:256) where it appears under its older nomination Accacia Albida Del. . The indigenous Gwembe Tonga name given is muUnga. Scudder says that its seeds are eaten, the pods used as fish poison and the wood used in dugout canoe construction.

One outstanding property of the tree is that it sheds its leaves in the rainy season. This, in combination with its fertilising properties makes it a perfect tree for inter-cropping  especially with maize. The CFU proposes a planting grid of 10 x 10 m, resulting in 100 trees in a hectare.

Now how good is this all in practice and what are the hitches? Below an account of my experiences with musangu and some thoughts and observations.

What we did

We planted about 350 musangu seedlings during the 2008-9 and 2009-10 rainy seasons. A number of these were procured at the CFU Choma office, others were grown by us from seed in plastic bags, following CFU instructions. The seed was procured at the CFU office. We planted three hectare where we do crop cultivation, using a slightly different grid as the one suggested by the CFU. We also planted a number of trees in non-crop area, out of curiosity, as boundary markers or for future as yet unknown use. Our soil is shallow and sandy, located in agro-ecological region I. Under the sand is gravel. Ground water level goes up to 3 m below soil surface in a good rainy season. We are about 1,200 m above sea level.

Freshly planted Musangu seedling. Note basin for trapping water and keeping manure, compost and mulch.

Planting

CFU provides suggestions for planting in its useful leaflet no 1. We planted the seedlings at the onset of the rainy season in small holes, about 25 cm deep, in which we would put some topsoil, manure, compost or MAP (= root growth promoting) chemical fertiliser; whatever we had. The seedlings were placed in a basin having a shallow bowl shape, so as to more effectively direct water to the root system. Where possible we use(d) pulled out weeds as mulching materials.
Based on experience I would now pay more attention to plant hole preparation; make them a bit bigger e.g. 25 x 25 x 50 cm or even deeper in area's with shallow soil, put more organic matter in, perhaps mixed in with some ant hill soil to improve on the water retaining capacity of our sandy soil. 

Watering

CFU advices 1 litre a week for seedlings in the dry season, for example by using the knap sprayer filled with water. In year 1 we watered many of them using a water bottle feeding system, supplying seedlings with about 1-2 l/week by a form of drip irrigation using bottles filled with water next to the seedlings stuck top down in the ground. Survival rate was good with only a few dying of drought. In year two we bucket-watered the basins having now over 1 year old seedlings with about 10 l preferably once every 2 weeks. We had almost no casualties because of drought but it is a lot of work. Trees in year tree dry season we gave about 20 l preferably once every 2-3 weeks. Again, this is a lot of work; you need to have the water, manpower, time & money. The reason why we opt for periodic thorough watering is to stimulate deeper root development. Typical irrigation problem: the basin in which the tree is growing must be maintained, have the right shape and depth. In practice workers often just water, more than is necessary or ineffectively, into a basin that is too big and flat. Clearly, this water nurturing must continue until the tap root has penetrated ground water level. As of year 4 we stopped watering the trees and to date the large majority of trees has survived. However, they remained small.   

Mulching

CFU supports mulching generally but does not mention it specifically as a means to supports the establishment of musangu seedlings and young trees. Yet the normal benefits of mulching also help the musangu: less evaporation of water, better absorption of water, less or no weeds, creation of topsoil.

Fertilisation

We fertilise preferably twice a year, certainly once with cow manure and in any case at the end of the rainy season when new leaf appears. We may also sprinkle some Zambian fertilisers formulation “C” – supporting root formation, having trace elements and 30% organic matter. CFU (as in the Jatropha case) does not suggest a fertilisation scheme. Yes, when you are among the lucky having naturally fertile soil it might be enough to plant seedling trees to see them rapidly develop. But in our case we had to supply additional nutrients.

Tree development

Seedling development into young trees has shown a stunning variety. Some seedlings hardly seem to grow; many conform to what, under the prevailing circumstances, appears to be “normal” development; some seem to be doing very well, being over 2 m tall. Normal development at our place would be about 0.75 to 1 meter tall for a 2.5 yr old tree. What you want, for a tree inter- cropped with maize or sunflower, is a tree having a straight stem eventually developing a canopy above the working surface. What I see is that many trees require training and support. The “central leader” tends to bend over and down. On this “leader” another branch starts to grow upwards resulting in a peculiar trunk segmentation. Seedlings and young trees also are sensitive to wind and therefore tend to grow up slanted following the prevailing direction of the wind. In order to promote regular more or less straight trunk development you need to prune the tree from time to time and support it with sticks. You need to collect the pruned material and burn it because of its thorns.

Musangu about two year old. Note near absence of leaf, picture is taken during rainy season. The tree is placed in a mulched basin and supported by a stick to promote vertical development.

A, and possibly the main factor in tree development is soil depth. You can improve the soil around the tree by organic means, you can add nutrients, you can give water in the dry season but there is little you can do about soil depth. If your soil is shallow and if the gravel or rocks under that shallow soil are so dense that the tree can not make a proper tap root it will not develop well and remain dependent on artificial watering. In that case your tree is in the wrong place and you'd better relocate it to a suitable location.

Diseases

Musangu, unlike the Jatropha, appears to be relatively disease free. We have had incidentally and rarely a tree seemingly afflicted by a white fungus. Ants like to "burrow" next to the tap root, but we have no incidence of trees dying because of ants or termites destroying them.

Some practicalities of the musangu grid

Planting the musangu in a grid, e.g., the 10 x 10 m proposed by the CFU, structures your land and this is very convenient for example in the calculation of seeding or fertiliser/manure requirements. It also is aesthetically pleasing. But in the first years your young trees are easily trampled by people or oxen doing their work. It is good to put sticks next to your small musangu trees to increase visibility. Make sure that necessary repairs be done immediately and have spare plants in the nursery.
In retrospect, however, I would decrease the distance between trees in the row to 5 meter; and possibly increase the distance between rows to 12 meter. If it comes to pass that the trees overcrowd each other in the rows you can always thin them as necessary. That might take some time, perhaps over 20 years.

Frost sensitivity

Musangu is a (sub)tropical tree that can withstand our "normal" winter but very definitely does not like frost. In our area we rarely do have night frost. The winter of 2011, however, was one such rare occasion with one night of true night frost. I live here since 1988 and it was the first time to experience this. It was not good for any musangu tree exposed to below zero temperature C. It did not kill them but in many cases destroyed the vegetation above ground level. Gradually new shoots emerged right above soil level, in a coppicing manner, developing rapidly. (One more reason to look well after water and nutrients!).

The time it takes to reap

To have the stated fertilising benefits one needs patience, and quite a bit of it, as well as foresight, and a long term perspective. The tree, under favourable conditions, can develop massively up to 30 meters tall with an immense, broad canopy. We do not have, it appears to me, in Choma district many places having such favourable conditions. However, at Bruce Miller's Nansai farm, some 20 km's north of Choma, well developed, mature trees can be seen. On poor soils the period that it takes for the musangu effect to result in substantial savings in cost of fertilisation is longer than the 10-12 years stated by the CFU. Perhaps it is wise to adjust the grid, sticking to 10 – 15 meter between the rows with a spacing of 5 meter within the row. One could imagine that tree spacing be related to local conditions.

Social constraints in Musangu propagation

CFU aims at 240,000 ha having the musangu cultivation system. The cultivators in very large majority are small scale, sometimes very small scale villagers farmers & rural households. I have, from a different position, experience in promotion of tree growing for village households in Southern Province. It concerned the malala tree (Hyphaene Petersiana), a palm tree used in basketry. Success rate was low to poor despite free dissemination of seeds and technical advice. Reasons:

1. Mobility / insecure future as regards residence. Mobility in the village / rural households can be quite high and is unpredictable. People move because of local frictions, death in the family, witchcraft, or perhaps just in search of greener pastures. Mobility was in fact a basic aspect of Tonga life and accounts for their territorial spread. You stand to lose “your” trees if you move, and traditional land (as it stands) is not for sale.

2. No guaranteed rights over land and hence your investment. People may have the right to cultivate a piece of land by traditional custom, but that right usually ceases when actual usage stops. Often there might be latent claims on the same piece of land that can be activated at any time and certainly at death. Such reasons obstruct having a clear right to ownership (your investment) in the trees planted and cultivated. In the traditional system you might be cultivating (rightfully) somebody else’s land, for example of the spouse. Also in such a case you’ll not be able to say: this is my land and those are my trees. The trees are an investment the returns of which need to be guaranteed in one way or another.

Propagating the “musangu system” without addressing the social constraints and conditions mentioned above is nearly pointless. Indeed, of all problems and constraints, this by far is “the most thorny issue.”

Assessment of Musangu

1. The tree indeed seems to be relatively easy to grow as far as susceptibility to pests and diseases is concerned.

2. Anticipated functionality might improve by developing strains that grow straight (also in Choma district).

3. It would be good if a fertilisation schedule is put in place related to soil types and location.

4. Same for irrigation.

5. Information should be provided about naturally optimum conditions for the musangu habitat (soil, water, altitude, temperature) and effect of significant deviation of these outside of the natural habitat; and measures to be taken to counteract these deviations. 

6. Alternatives to the 10 x 10 m planting schedule should be considered on the basis of expected tree development. There are area's where the tree is not going to reach giant size, and it might also make sense to opt initially for closer spacing within the row and thin later as or if necessary.

7. Check before planting your soil and soil depth, and the gravel and rocks underneath. Don't plant If it appears that the tree shall not be able to make a tap root that can reach ground water level. Indeed, if the musangu cannot grow well on your land you may ask yourself if it makes sense to grow commercial crops on that land. You may be better off leaving it to cattle.

8. Social constraints in the cultivation of the musangu must be considered and addressed. This applies to areas where land can only be cultivated under customary law, meaning land that is not owned nor has “title.” The large majority of the CFU target group has the "right to use" land because of actual usage and that right ceases when usage ceases.


Post Scriptum
Attached comment by experienced agricultural researcher Franz Ulrich Fischer confirms that musangu can be cultivated outside of its natural habitat, but to do this successfully (in sandy Choma soils) one needs to create favourable conditions as by watering, soil preparation and fertilisation.