Locust bean pod extract, a binder for landscape construction in Nigeria

Introduction

 Locust bean pod extract is a Waste Agricultural Biomass(WAB) obtained from the fruit of the African locust bean tree (Parkia biglobosa), which is the material resource required to produce Locust Bean Pod extract (LBPE). The harvested fruits are ripped open while the yellowish pulp and seeds are removed from the pods; the empty pods are the needed raw material. The pods make up 39% of the weight of the fruits, while the mealy yellowish pulp and seeds make up 61% (Adama and Jimoh, 2011).

The African locust bean has a wide distribution across Sudan and Guinea Savanna of the African ecological zones. The range extends from the western coast of Africa in Senegal across to Sudan. The tree can be found in nineteen African countries, such as Senegal, Gambia, Guinea Bissau,Guinea, Sierra Leone, Mali, Cote De Voir, Burkina Faso, Ghana, Togo, Benin,Niger, Nigeria, Cameroon, Chad, Central Africa Republic, the Democratic Republic of the Congo, Sudan and Uganda. In Nigeria, it occurs in the northern part of the country. The locust bean pod extract and its solutions are used for landscape construction in the country.

Study Area

The study was conducted at two sites. The first is the city fencing in Kofar na’isa, Kano State, shown red in Plate I. Plate II identifies the second study area in Yarfi Town, Jigawa State and the relative locations of the Yarfi town gate and the sun-dried brick factory.

Methodology

The processes used in generating, processing, and presenting data for the research were mixed methods (CR Kothari 1995), which include qualitative and quantitative approaches. The qualitative approach included a reconnaissance survey, field data collection, and accessing secondary desktop data. The quantitative method involved satellite image processing and analysis.

 Reconnaissance Survey

First, a familiarity visit to the area under investigation was carried out. Kofar na’isa was visited five times in August and September 2022 and Yarfi Town was visited three times in July and August 2022. During these visits, the required site-specific information was obtained from the local people. The purpose of the survey was to identify the main locust bean, locust pod extract solution, and their application in landscape construction.

 Field Data Collection

After the comprehensive reconnaissance survey, and Google images of the study areas were downloaded using a Google earth pro image Landsat Copernicus 2022. These images enabled the researcher and other participants to have clear idea of the project locations.

 Locust Bean

The locust bean is a perennial deciduous tree in the family Fabaceae and grows in a wide range of environments across Nigeria and other African states.  It is grown primarily for its pods, which contain a sweet pulp and valuable seeds. When crushed and fermented the seeds constitute an important economic boost for the region. Other parts of the tree are harvested for food and medicinal applications. The locust bean may also positively affect the yield of other nearby crops as the fix nitrogen in the soil. The tree grows at altitudes between 0-300 metres, and requires mean annual rainfall of between 400-700 millimetres and a mean annual temperature of around 24-28°C. It prefers well-drained, thick clayey soils but is also be found in shallow, thin sandy soils. Plate III shows the various components of the tree, including its flower, pod bunches and extract.

Content of Locust Bean Pod Extract

 The utility of locust bean pod extract in landscape and building applications is on the rise. Aguwa and Jimoh (2012) investigated how locust bean pod extracts would affect the compressive strength of lateritic and sand crete blocks. The findings indicated that the compressive strength of the blocks increased by an impressive 78.5%. Table 1 below identifies the chemical composition of locust bean pod extract.

Table 1: Chemical composition of locust bean pod extract

‍Processing of Locust Bean Pod Extract

Information obtained from the people at the study sites, indicate that the pods are collected and soaked in water for at least four to seven days to obtain the extract. It can also be gained through the leaching process of boiling the pods which leaches out the binding materials from the pods. Plate IV shows the locust bean pod before being soaked in water, and Plate V shows it after the water has been removed. Plate VI shows the resultant extract.

Locust Bean Pod Extract as a Replacement for Water in Sand Mortar

The pods are usually measured and soaked in water, which has been identified as the best extractor (Abagale, Twumasi and Awudza, 2013).The period of the soaking process that derives the maximum strength in sun-dried blocks production, is four days (Kareem, 2010). The pod solution obtained after the required soaking period is then mixed into a sand mortar as a replacement for ordinary distilled water. This process can be carried out at different concentrations of the pod extract, which usually is expressed in kilogram per litre. Much research has been done using the locust bean pod extract as a binding agent (Aguwa, 2012; Adama and Jimoh, 2011) and Aguwa (2012) found that there is a correlation between locust bean pod extract concentration and the strength of lateritic blocks. Higher concentrations resulted in greater compressive strength of blocks.

 The uses of Locust Bean Pod Solution in Landscape Construction

The use of locust bean pod extract is recommended by many northern Nigerians in the following applications:

 Sand Mortar: Sand mortar is typically a poor-quality mortar used for the making of sun-dried bricks and in the construction of structures, fences (walls), town gates and other landscape elements. However, indigenous people have used bean pod solution to strengthen and improve the quality of sand mortar. Plate VII below shows the mortar after locust bean pod extract solution has been added to it.

‍Sun-dried Bricks:  In northern Nigeria, sun-dried clay bricks are of inferior quality. They are used to build houses, walls and other landscape elements. However, the bricks are not suitable for wet areas. The bricks are usually ground-moulded and sun-dried.The surface of this type of brick is rough, and they have uneven edges, as illustrated in Plate VIII. But the process of adding locust bean pod extract to the mortar before moulding the bricks, results in its strength development.

City Fencing: The city fencing of Kofar na’isa has been in existence since the 14th century.  It was built with sun-dried bricks and sand mortar, where a locust bean pod extract solution served as water for the brick moulding and the mortar. This process made the wall stable and durable for an extended period. The wall is illustrated in Plate IX.

Town Gate:The creation of a central town entrance is one of northern Nigeria’s urban traditions. Every individual coming to the town must pass through such a gate for security reasons. The gate, like the fencing, was constructed with sun-dried bricks and sand mortar, using a locust bean pod extract solution instead of water, which resulted in a durable structure. The Yarfi town gate is illustrated in Plate X.

Garden Seat:  This same technique is used in a dismountable garden seat illustrated in Plate XI. The benefit is that the bricks resist rain. are strong and easily support the timber seat and its occupants.

The Effect of Locust Bean Pod Extraction Sun-Dried Bricks used for Wall Fencing

The people of northern Nigeria used to apply such locust beans pod extract to counter the impact of rain on the wall. When it rains, the locust pod bunches, located at the top of the wall, saturate, and then drain extract liquid onto it. The residual stain then protects the wall from erosion. This technique is shown in Plate XI.

‍Finding

The result of the study shows that the locust bean pod extract solution is used to strengthen sand mortar and sun-dried bricks if applied at the correct concentrations. Wall fencing erosion is prevented when locust bean extract is applied.

‍Conclusion

This simple technology has been in existence since the 14th century in northern Nigeria, however, its use has not been properly documented or described.  Those people using the technology do so because they have inherited it from their forefathers and because it serves the purposes of strengthening their local landscape constructions and preventing their wall fencing from the yearly eroding effects of rain. The appreciation of indigenous knowledge and how it leads to sustainable and cost-effective solutions should be more appreciated.  Landscape architects, in particular, should put more effort into finding out about indigenous landscape solutions that exist in  their region. These solutions would be cost-effective and keep people in touch with their local species and environment, helping them to appreciate and protect these valuable plant species.

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