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Rocks for Crops: Agrominerals of sub-Saharan Africa
Abstract
The book 'Rocks for Crops' introduces the applied, goal-oriented, natural resource science of agrogeology. Agrogeology is the study of geological materials and processes that contribute to the maintenance of agro-ecosystems. Agrominerals are naturally occurring geological resources for the production of fertilizers and soil amendments. The inventory of indigenous agrominerals resources from 48 countries in sub-Saharan Africa are reported.
... Basaltic rocks, a common constituent of the Earth's crust, have recently received much attention owing to their agronomical and environmental benefits (Beerling et al., 2018;Gillman et al., 2002;Harley & Gilkes, 2000;Van Straaten, 2002). Given the high dissolution rate relative to other rock types makes basaltic rock becomes a potential fast-reacting additive for soil improvement (Conceição et al., 2022;Panhwar et al., 2014) and robust crop yields (Conceição et al., 2022). ...
Application of basalt powder (BP) for agricultural soils has been increasingly encouraged owing to its positive effects on soil fertility and carbon sequestration capability. However, the onsite positive effects can be reduced if BP or its components are prone to dispersion and losses by surface run‐off or downward leaching. In this study, surface charge (SC), colloidal properties together with dispersion/aggregation phenomena of BP were determined in a systematic approach, considering co‐effects of pH and ionic strength, presence and variation of various common mono‐, di‐ and trivalent cations and anions. Possible scavenging abilities of BP for common environmental heavy metal pollutants such as Cu ²⁺ , Pb ²⁺ , Zn ²⁺ and AsO 4 ³⁻ were also elucidated. We found that BP possesses negative SC; hence, it is prone to dispersion in the environment with the predominantly negatively charged soil compounds. Cations tended to reduce negative charges of BP; hence, they facilitated BP aggregation. In contrast, anions showed opposite tendencies in which BP was favoured to disperse. We also found strong adsorption capabilities of BP for Pb ²⁺ , Cu ²⁺ and Zn ²⁺ as well as anionic AsO 4 ³⁻ , inferring that BP can act as a sink or interfere with the transport route of heavy metals in soil‐aquatic environments. In general, the findings suggest that our ambition to use engineered BP for boosting soil fertility and carbon sequestration also needs to consider the dispersibility of BP upon soil application since this process can enhance nutrient losses or heavy metal widespreads through co‐transports with BP.
... In addition, farmers incur increasingly higher input costs arising from volatile domestic currencies affecting profit margins (Goldblatt, 2010). Sustainable and productive farming is the foundation for the development, maintenance, and well-being of society on a national and global scale (Van Straaten, 2002). Daniell and van Tonder (2023) emphasize that soils are the basis of employment and food/nutritional security in South Africa, therefore, it is necessary to manage land resources by implementing a combination of sustainable and innovative strategies that improve and maintain soil fertility. ...
Agriculture and other land use practices have severely affected the quality of soils and food production systems in South Africa. In addition, these practices significantly contribute to greenhouse gas (GHG) emissions. Soil quality is generally associated with soil organic matter (SOM) along with elemental Carbon (C) and Nitrogen (N). Approximately 58% of South African soils contain <0.5% organic C, 38% contain 0.5–2% organic C, and 4% contain >2% organic C. The extensive aridity and lack of SOM content in South African soils cause them to lack resilience and have a delicate nature compared to soils in temperate regions. In a country where almost 60% of the land is degraded, and 91% is prone to desertification, farming practices require a revised framework for land management. The challenge of producing food on degraded land that is often water-scarce and particularly vulnerable to the effects of climate change is a threat to South Africa's food and nutritional security. Therefore, this review aims to equip farmers with knowledge and principles of innovative and sustainable alternatives such as regenerative agriculture that naturally and progressively improves soil quality/fertility and ecosystem health; and reduces GHG emissions through carbon sequestration. Quantitative studies in South Africa show that during 5–90 years of crop cultivation in the Free State province resulted in a 10–73% reduction in C and N relative to natural grasslands. Similar studies reported a 50% reduction in C after 50 years of cultivation on Hutton soil in Pretoria; and a 50% reduction in C after only 3.5 years of cultivation in the Free State. Considering that the world's food systems are responsible for more than a third of anthropogenic GHG emissions, we are convinced that the shifting trend toward regenerative agriculture is a sustainable climate-smart solution for global food production systems.
... Most of the soils in Western Ethiopia are acidic with pH ranging from 5.5-6.7 (Van Straaten, 2002). According to Wortmann et al. (2003), the availability of nutrients in the soil is highly influenced by pH. ...
Low crop productivity, mainly caused by low soil fertility and absence of efficient and sustainable soil fertility management practices, is a major constraint contributing to food shortage in Ethiopia. Though several limitations restrict its use by small scale farmers, the use of inorganic fertilizers has been suggested as one of the best approaches to address this problem. This study was conducted in Western Ethiopia to assess the perception of farmers regarding the status of the soil, soil fertility problems and important factors in the use of inorganic fertilizer using semi-structured questionnaires. The result showed that farmers identified reddish brown and black soils as the predominant types of soils in the survey area. Most farmers were aware that the fertility of the soil and the amount of fertilizer used in their farms were declining over the last five decades. The highest proportion of farmers reported to have problems in obtaining fertilizer at the right planting time. In addition, the high cost of fertilizer was identified as one of the most important factors that hindered the use of inorganic fertilizer by farmers. The majority of respondent farmers identified farmers' cooperatives as the major supplier of fertilizer. However, the highest proportion of respondent farmers (30.6%) rated the quality of service of farmers' cooperatives as bad. Hence, as a major supplier of fertilizer in Ethiopia, farmers cooperatives need to improve the quality of their service in supplying fertilizer to farmers.
... Liming materials, such as limestone, marble, marl, and dolomite, which contain calcium carbonate or magnesium carbonate, are often used in Ethiopia to address soil acidity problems and enhance crop productivity [10]. These materials neutralize soil acidity by reacting with surplus hydrogen ions (H þ ) in the soil [11]. Wukro limestone and Sheba marble from the Tigray Region were used to remediate soil acidity in northern Ethiopia. ...
Biochars were produced at 350 °C and applied at varying rates (0, 52, 104, and 156 Mg ha⁻¹ and incubation times up to 120 days. Both biochars and limestone significantly improved soil properties like pH, electrical conductivity, cation exchange capacity (CEC), and nutrient availability. Limestone proved most effective, raising pH by 1.3 units on average and increasing EC and CEC, followed by Cadia purpurea- and Tarchonanthus camphoratus-based biochars. Biochars also increased pH, with Cadia purpurea showing the greatest effect (up to a 1.49 unit increase at the highest rate of application). These findings suggest biochar from these expansive plants holds promise for improving acidic soils. However, the optimal application rate, incubation times, and type of amendment (biochar or limestone) likely depend on specific soil characteristics and goals. Further research is needed to explore long-term effects, combined amendment approaches, and cost-effectiveness for long-term soil health, agricultural productivity, and environmental well-being.
Rice production in sub-Saharan Africa (SSA) is restricted by low water availability, soil fertility, and fertilizer input, and phosphate rock (PR) application is expected to increase production. Soil water conditions and soil types affect the efficacy of phosphorus fertilization in improving productivity. However, these factors are rarely discussed together. In this study, we aimed to investigate the soil types and soil water conditions in the fields, as well as their effects on rice productivity after phosphorus fertilization, and optimize the findings using remote sensing techniques. A soil profiling survey, followed by a field experiment in seven farmer fields, was performed in the Central plateau of Burkina Faso. The following treatments were applied: nitrogen and potassium fertilization without phosphorus (NK), PR application with NK (NK+PR), and triple super phosphate (TSP) application with NK (NK+TSP). Submergence duration and cumulative water depth were recorded manually. The inundation score, estimated using a digital elevation model, explained the distribution of soil types and soil water conditions and correlated negatively with sand content and positively with silt and clay content, indicating an illuvial accumulation of fine soil particles with nutrient transportation. The field experiment showed that although grain yield was significantly restricted by phosphorus deficiency, the increase in yield after phosphorus fertilization was higher in Lixisols and Luvisols than in Cambisols because of the low Bray-2-phosphorus content of Lixisols and Luvisols. The inundation score correlated positively with grain yields after NK+PR and NK+TSP treatments. In conclusion, soils with low inundation scores (mainly Lixisols and Luvisols) showed a drastic increase in grain yield after TSP application, whereas those with high inundation scores showed comparable yields after PR and TSP application despite the low phosphorus fertilization effect. Our findings would help optimize fertilization practices to increase rice productivity in SSA.
Assessment of the genetic variability of soybean genotypes under low soil phosphorus (P) conditions provides an understanding of the genetic potential of the genotypes to improve the crop for low P tolerance. The study was designed objectively to estimate the extent of genetic variability of soybean genotypes for low P tolerance. Thirty six soybean genotypes that were introduced from various sources were grown in simple lattice design with three replications at three locations in Western Ethiopia characterized by P-deficient-acidic soils. It was revealed that weight of 100 seeds; plant height, root and biomass fresh weight exhibited relatively high heritability and genetic advance on low P soils. Principal component analysis also revealed that the first five principal components (PCs) accounted for more than 85% of the total variation. The first principal component that contributed for 37.7% of the total variation was influenced by root fresh weight, tap root length, root volume, fresh biomass weight, days to maturity and days to flowering in the order of importance; indicating the significance of these traits for low P tolerance screening. Cluster analysis grouped the genotypes into four clusters. Observation of large variation and relatively high heritability indicates that selection would be effective to improve soybean varieties for performance on P stressed soils and identify low P tolerant varieties that helps smallholder farmers optimize soybean productivity on P deficient soils. Abush et al.
Due to the escalating demand for conventional potassium sources, and their unavailability in many African countries, there is a growing interest in hydrothermally treated igneous rocks as viable alternatives. These materials exhibit promising potential in enhancing potassium release, comparable to traditional sources like muriate of potash (M.O.P.). However, it remains uncertain whether they can adequately fulfill the nutrient requirements of plants. In this study, we evaluated nutrient balance in ryegrass (Lolium multiflorum) using raw and hydrothermally treated K-bearing silicate rocks as fertilizers. The Compositional Nutrient Diagnostic (CND) approach was used to assess the plants’ nutrient status, involving identification of high-yield subpopulations, and setting a yield cutoff. We derived a theoretical threshold for nutrient imbalance (CNDr2) using statistical methods like the chi-square distribution function and low-yield subpopulation proportion. CNDr2 was validated via Cate–Nelson partition and sum of squared individual nutrient indexes. Results showed a yield cutoff of 37.759 kg ha−1, distinguishing low-yield and high-yield subpopulations based on cumulative variance ratio functions from survey data. The theoretical threshold derived using the chi-square function was 10.1, subsequently validated by the Cate–Nelson method. Critical CND nutrient indices were symmetrical around zero, but their sum indicated foliar nutrient imbalance, notably zinc, potassium, and copper excess, attributed to 20 interactions identified (4 synergetic and 16 antagonistic). This study underscores hydrothermal treatment’s efficacy in improving nutrient availability and achieving a balanced nutrient profile compared to raw materials. It offers a promising solution for enhancing agricultural productivity, especially in tropical regions like Africa, where traditional sources are scarce.
Purpose: Salt-affected soils have significant enough salt concentrations to impact other land and
soil resource uses, plant health, soil characteristics, and water quality. Consequently, a study was
carried out in the South Ethiopian Rift Valley area around the lakes of Abaya and Chamo to
determine the intensity and the types of salt-affected soil and map their spatial distributions.
Methods: At 0–20 cm depths, a grid soil sampling scheme was employed to gather data from
agricultural soils affected by salt. An adequately spaced grid cell of 200 m*200 m or seven
transects, with seven samples collected every 200 m on each sampling site, was generated by the
QGIS software’s Fishnet tool, and an auger collected 226 soil samples from the proposed 245 soil
sampling points. The analysis and interpretation of the data were done using both statistical and
geostatistical methods. The un-sampled surface was predicted and mapped from laboratory point
data using the standard Kriging algorithm in QGIS.
Results: According to the results, the soil in the study area was rated as strongly alkaline and
moderately alkaline in the reaction. The coefficient of variation (CV) was the lowest for soil pH.
Except for the Ganta Kanchama site, low CV (<10 %) confirmed the similarity of pH values
throughout all research areas. The EC values depicted that the study area is slightly saline except
for the Ganta Kanchame site, which rated moderately saline to strongly saline. The variability of
soil EC rated moderate to strong variation for the studied area. The exchangeable sodium percentage
(ESP) values distribution between the study sites demonstrates considerable variability
and difference. The area is dominated by low to high-risk rate soil sodicity, as evidenced by the
soil ESP CV of the studied area, which was >100 % and showed significant variability among the
samples. Out of 2274.65ha of the studied area, the type of salt 62.28 %, 26.09 %, 10.99 %, and
0.63 % were categorized as non-saline non-sodic, saline-sodic, sodic, and saline, respectively.
Following saline-sodic, sodic, and saline soils, respectively, non-saline and non-sodic soils
comprise most of the investigated areas.
Conclusions: The result indicates almost all the salt-affected areas were situated in relatively lower
slope areas exhibiting a flat to almost flat slope (0–2%). The study’s findings are that the studied
area needs specific soil management strategies to boost the salinity and sodicity problems around
the study area and recommended reclamation techniques as the extent of the problems.
Soluble fertilizers, particularly potash, are often prohibitively expensive or unavailable in Africa. Consequently, alternatives such as powdered silicate rocks, both raw and hydrothermally treated, are being explored as potential solutions, especially for acidic tropical soils. This study investigates the possible impacts of these rocks (syenite) on groundwater quality, which is a critical factor for agricultural activities. The powdered raw material underwent chemical and mineralogical characterization, including X-ray fluorescence and X-ray diffraction, followed by quantitative evaluation of materials by scanning electron microscopy. Both raw and 46 hydrothermally treated materials were subjected to sequential leaching cycles (1, 24, and 192 hours) using deionized water, and the resulting leachates were analyzed by inductively coupled plasma atomic emission spectroscopy. Parameters such as electrical conductivity, total dissolved solids, soluble sodium percentage, sodium adsorption ratio, magnesium hazard, Kelly's ratio, and permeability index were also evaluated. Results from the 47 leachates indicated that 64% of the samples exhibited excellent to acceptable water quality for irrigation purposes across all parameters. Conversely, 6% to 13% fell into the doubtful category, and 2% to 24% were classified as unsuitable. Consistency index and ratios of approximately 0.07 and 0.042, respectively, were determined using multi-criteria decision analysis (analytic hierarchy process: AHP), confirming the coherence of the decision and pairwise comparison matrix. The weighted coefficients for each criterion ranged from 0.06 to 0.2. Consequently, the optimal sample (Treatment 23) was identified, showing a hydrothermal temperature of 176°C, a time of 3.9 hours, a normality of 4.62, and a liquid-solid ratio of 0.24. This treatment met all high-water quality standards, including low salinity and sodium hazard, as corroborated by the US salinity laboratory and Wilcox diagrams. Furthermore, due to their nutrient release, low concentration of toxic elements, and effective buffering capacity (pH ~ 10.6), these powdered syenites are suitable for application in acidic soils.
Keyword: Hydrothermal treatment, syenite rock, sodicity, salinity, groundwater quality, multi-criteria decision analysis (AHP)
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