Characterization of dolomite rock deposits in Musumba-Cibitoke for their suitability as agricultural lime

Abstract

Soil acidity is a significant handicap to agricultural productivity in Burundi, affecting soil fertility, crop yields, and food security. Agricultural lime (ag-lime) is one of the solutions for neutralizing such acidity, but the rate of ag lime production is still inadequate, meaning that its availability and affordability remain limited due to low local material sources. Despite the existence of dolomitic rocks that could be used for the production of agricultural lime in Musumba-Ruhagarika, Cibitoke Province, their characterization and utilization have not yet been done. Their chemical and physical properties remain unknown. This study aimed to investigate the characteristics of this deposit, to evaluate the contents of the chemical and physical properties, and to determine their suitability for the production of agricultural lime. Twenty-seven (27) rock samples of 4 kg each were collected from 9 sample points using systematic random sampling over an area of 1 km², 200 meters apart from one sample point to another within Musumba and four (4) soil samples were randomly collected from a plot of 400 m² located in Mutumba, Bujumbura before and after dolomite rock application on the soil. These samples were analyzed in three national laboratories using X-ray fluorescence (XRF) analysis for the rock chemical properties including calcium oxide (CaO), magnesium oxide (MgO), impurities and trace elements such as MnO, Fe2O3, Al2O3, SiO2, SO3, K2O, CuO, P2O5, and SrO, and using gravimetric method at 800oC for the Loss on Ignition (LOI) determination. The rock and soil pH were determined using a direct reading method with a sample-to-water ratio of 1:5. For the physical analysis of the rock, the absolute density was determined using pycnometer method, and water absorption using sample wetting and drying method. Results from the analysis showed an average content of 71.65% CaO, 19.89% MgO, and a rock pH of 9.66, indicating an alkaline rock composition. The soil pH increased from 5.24 to 7.335 during the field trial experiment. The average LOI of 45.43% confirmed high carbonate content of the rock, while physical analyses showed density of 2.84 g/cm³ and low water absorption of 0.78%. Semi-variogram and kriging models were used to plot and show the variability and spatial distribution of each property within the study area. The Calcium Carbonate Equivalent (CCE) and Purity Index (PI) values were determined and computed from chemical results and showed that CCE is high, with an average of 169.3% and PI average of 94.3%, which confirmed the dolomitic limestone nature and high acid neutralizing capacity of the rock, making it an effective amendment for the soil.