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There is a lack of long-term field approach investigating biochar impact on soil properties and vegetation, particularly in forest ecosystems. Relic charcoal hearths (RCHs), the result of the historical charcoal production in the forests, preserve a charcoal-enriched topsoil horizon, thus representing a suitable proxy for studying the long-term effect of biochar addition to soil. In this study, we analyzed the chemical properties of a soil as impacted by charcoal accumulation in three RCH plots in southern Wallonia (Belgium) compared to the soil outside RCHs. We further evaluated the effects of RCHs soil properties on the growth performances of silver birch and European beech as well as the leaves’ nutrient concentration of the latter. RCHs soil stored much more carbon and nitrogen than the reference ones. Most of the C in RCHs derived from charcoal (70‒94% of total organic carbon), which would correspond to a total input of 342 tons of biochar per hectare in these soils. Such an accumulation of charcoal still affects nutrient status of soil even after 150 years since charcoal hearths abandonment: CEC and K, Ca, Mg, Na, Mn and Zn concentration remained higher in RCHs soil compared to the reference one. In spite of a seemingly higher fertility of RCHs soil, elemental concentrations of European beech leaves grown in RCHs did not show any significant difference compared to the reference plots, except for C and Mn concentration, higher and lower, respectively, in the leaves of European beech trees grown inside than outside RCHs. Overall, RCHs soil chemical properties were not a decisive factor in significantly improving tree growth. On the contrary, tree ring width average values of both tree species was slightly lower in RCH plots, suggesting to better investigate the potential long-term detrimental effect of a large biochar addition to soil on forest trees.

Black carbon (BC) plays an important role in terrestrial carbon storage. Nevertheless, the effect of cultivation on long term dynamics of BC in soil has been poorly addressed. To fill this gap, we studied the chemical properties of charcoal particles extracted from preindustrial kilns in Wallonia, Belgium, along a chronosequence of land use change from forest to agricultural soil, up to 200 years of cultivation. Preindustrial charcoal samples were compared with charcoal subjected to short term ageing in a currently active kiln. Cultivation increased the association of charcoal with soil minerals, which is favored by deprotonation of carboxylic acids under liming, thereby enhancing the reactivity of charcoal toward mineral surfaces. The large specific surface area of charcoal, related to its porosity, promotes the precipitation of 2:1 phyllosilicates and CaCO3. Both ageing and cultivation decreased the resistance of charcoal to dichromate oxidation, related to an increase in the H/C of charcoal. Differential scanning calorimetry revealed the presence of three fractions of distinct thermal stability. Saturation of carboxylate groups with Ca2+ under liming decreased the thermal stability of the O-rich, less thermally stable fraction of charcoal. This fraction decreased over time of cultivation, leading to a relative accumulation of the thermally most stable fraction of charcoal. This might result from the preferential loss of the O-rich fraction or the slowdown of charcoal from oxidation via association with minerals. Our results highlight the idea that land use significantly affects the properties of BC through the modification of soil conditions, which might influence the kinetics of BC loss from soil.

Black carbon (BC), the solid residue of the incomplete combustion of biomass and fossil fuels, is pervasive in soil and contributes to critical soil functions. Therefore, soil amendment with artificial BC (biochar) is more and more regarded as a means to mitigate greenhouse gas emissions while improving sustainably soil fertility. Nevertheless, the long-term fate of BC in soil is still poorly understood. In Wallonia, Belgium, intensive in situ charcoal production affected a main fraction of the forested area in the late 18th century. The topsoil of pre-industrial charcoal kiln sites is largely enriched with charcoal residues, which offers the opportunity to evaluate the long-term effect of BC on temperate soil properties. We sampled the soil of 40 pre-industrial charcoal kiln sites from forest and cropland. Soil properties were compared to that of adjacent reference soils, unaffected by charcoal production, and to soil characteristics at a currently active kiln site to trace the evolution of soil properties over time. We also studied the properties of charcoal particles extracted from soil along a chronosequence of land use change from forest to cropland. Dynamic thermal analysis and chemical oxidation were used to investigate the stability of aged charcoal particles and to discriminate between charcoal and uncharred soil organic matter (SOM) in the soil of charcoal kiln sites. The content of charcoal and uncharred SOM was related to the availability of nutrients, acidity, cation exchange capacity and microbial activity, biomass and community structure of soil. Overall, we highlighted that the features of charcoal and its effect on soil properties evolve over time and depend on soil conditions. BC is very persistent in soil, therefore, long-term implications of soil amendment with biochar should be further addressed before allowing its large-scale application., (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2017

The “Walkley-Black” oxidation with dichromate is a routine protocol for the estimation of soil organic carbon (SOC) content. Dichromate oxidation is also used to quantify black carbon (BC) in soil and sediments based on the larger resistance of BC to dichromate oxidation than uncharred SOC. The aim of this study was (i) to evaluate whether dichromate-based SOC quantification methods discriminate between uncharred SOC and charcoal residues in the topsoil of pre-industrial charcoal kiln sites and (ii) to test the influence of aging on the recovery of charcoal by dichromate oxidation. We selected 40 topsoil samples from 20 pre-industrial charcoal kiln sites of Wallonia, Belgium, and adjacent reference soils unaffected by charcoal production. Samples included soils from forest and cropland, with a diversity of soil types and textural classes. SOC content was estimated by the original Walkley-Black procedure (results were multiplied by the traditional correction factor of 1.32), and by an adapted method that includes external heating of the digestion mixture to overcome incomplete oxidation of uncharred SOC and get rid of the correction factor of 1.32. Results were compared to the amount of total organic carbon (TOC) content, measured by dry combustion, and to the content of charcoal-C in soil, estimated by differential scanning calorimetry. The soil of a currently active charcoal kiln site was also analyzed and used as a reference subject to limited aging. 23.6% of charcoal-C was recovered by the Walkley-Black procedure in the soil of the currently active kiln site against 65% for the soil of pre-industrial kiln sites, which indicates that the resistance of charcoal to dichromate oxidation decreases with aging. The recovery of charcoal increased to 90% after boiling of the digestion mixture, providing evidence that heat catalyzes the oxidation of charcoal. The substantial oxidation of charcoal by dichromate and the variability of recovery according to the degree of alte

Black carbon (BC) plays an important role in terrestrial carbon storage. Nevertheless, the effect of cultivation on long term dynamics of BC in soil has been poorly addressed. To fill this gap, we studied the chemical properties of charcoal particles extracted from preindustrial kilns in Wallonia, Belgium, along a chronosequence of land use change from forest to agricultural soil, up to 200 years of cultivation. Preindustrial charcoal samples were compared with charcoal subjected to short term ageing in a currently active kiln. Cultivation increased the association of charcoal with soil minerals, which is favored by deprotonation of carboxylic acids under liming, thereby enhancing the reactivity of charcoal toward mineral surfaces. The large specific surface area of charcoal, related to its porosity, promotes the precipitation of 2:1 phyllosilicates and CaCO3. Both ageing and cultivation decreased the resistance of charcoal to dichromate oxidation, related to an increase in the H/C of charcoal. Differential scanning calorimetry revealed the presence of three fractions of distinct thermal stability. Saturation of carboxylate groups with Ca2+ under liming decreased the thermal stability of the O-rich, less thermally stable fraction of charcoal. This fraction decreased over time of cultivation, leading to a relative accumulation of the thermally most stable fraction of charcoal. This might result from the preferential loss of the O-rich fraction or the slowdown of charcoal from oxidation via association with minerals. Our results highlight the idea that land use significantly affects the properties of BC through the modification of soil conditions, which might influence the kinetics of BC loss from soil.

In Wallonia, Belgium, intensive in situ charcoal production that was linked closely to pre-industrial smelting and steel-making affected a large part of the forested area in the late eighteenth century. Charcoal kiln relics can be detected under forest as domes of about 10 m in diameter, with the topsoil greatly enriched with charcoal residues. We sampled 19 charcoal kiln sites and the adjacent reference soil by soil horizon on four different soil types (Arenosols, Luvisols, Cambisols and Podzols). Data were analysed with linear mixed models to assess the effect of the charcoal kiln site on soil properties in relation to depth and soil conditions. We also addressed the evolution of soil properties over time by a comparison of the soil characteristics at a currently active kiln site. The charcoal-rich topsoil has a larger C:N ratio and cation exchange capacity (CEC) per unit of organic carbon than the reference soil. The largest CECs per unit of carbon were observed on soil with coarser textures. On acidic soil, the increase in base saturation in the subsoil reflects the past liming effect of ash produced by wood charring, whereas the topsoil is re-acidified. The acidity of carbonate-rich Cambisols, however, is not reduced. Regardless of soil type, the kiln topsoil is greatly depleted in exchangeable K+ and available P, which may be attributed to the small affinity of the exchange complex of charcoal for K+ and a decrease in P availability with time. Therefore, we recommend further research on the long-term effects of biochar on the dynamics of plant nutrients.

Research on biochar has increased, but its long-term effect on the fertility of temperate agricultural soil remains unclear. InWallonia, Belgium, pre-industrial charcoal production affected former forested areas that were cleared for cultivation in the nineteenth century. The sites of traditional charcoal kilns, largely enriched in charcoal residues, are similar to soil amended with hardwood biochar more than 150 years ago. We sampled 17 charcoal kiln sites to characterize their effect on soil properties compared with adjacent reference soils. Charcoal-C content was estimated by differential scanning calorimetry. The kiln soil contains from 1.8 to 33.1 g kg−1 of charcoal-C, whichmarkedly increases organic C:N and C:P ratios. It also contains slightly more uncharred soil organic carbon (SOC) than the reference soil, which accords with larger total N content.We measured a small increase in nitrates in the kiln soil that might relate to greater mineralization and nitrification of organic N. Frequent application of lime raised the pH to values close to neutral, which offset the residual effect of charcoal production on soil acidity. A cation exchange capacity (CEC) of 414 cmolc kg−1 was estimated for charcoal-C, whereas that of uncharred SOC was 213 cmolc kg−1. Despite the large CEC of the kiln soil, exchangeable K+ content was no different from the adjacent soil, whereas exchangeable Ca2+ and Mg2+ contents were considerably larger. Charcoal enrichment has little effect on available, inorganic and total P, but it can form strong complexes with Cu, which reduces the availability of the metal. Biochar is very persistent in soil; therefore, long-term implications should not be overlooked.

The excessive use of nitrogen (N) fertilizers has turned into a major environmental and economical concern today. Rice cultivation is particularly prone to N losses. The knowledge of the genetic determinism of agronomical nitrogen use efficiency (aNUE) and its two components - absorption (aNUE) and physiological (pNUE) nitrogen use efficiency - in rice is lacking and might be useful for breeding purposes towards the development of sustainable agriculture. In this study, the genetic determinism of NUE and related traits were investigated in rice through physiological and genetic approaches. The analysis of components of NUE and related traits in different rice cultivars in hydroponics demonstrated that agNUE depended more on aNUE than on pNUE. The sensitivity to the N supply depended on the rice cultivar. The genetic analysis was made on 174 F9-10 recombinant inbred lines (RILs) derived from the cross IR64/Azucena. Hydroponic experiments at the vegetative stage allowed the detection of 14 QTLs for NUE components and 63 for 12 agronomical and physiological traits. The aNUE was shown to be the most important component of agNUE in this RIL population. Six hotspots containing several QTLs for NUE or at least one for NUE and one for another trait were identified. Furthermore, 8 QTLs for aNUE or agNUE and 7 for other traits were found in several experiments repeatedly. Pot and field experiments allowed to identify 87 QTLs for NUE components and 371 for other traits in the same RIL population. Once again, aNUE was shown to be the most important component of agNUE. Fifty four hotspots were identified, and 9 QTLs for NUE components and 3 for other traits were found in several experiments repeatedly. In conclusion, the present study allowed to identify reliable regions involved in NUE components and related parameters in rice. These regions will be the target of further fine mapping and candidate gene studies towards the development of rice cultivars for sustainable agricultur, (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2014

Although salinization of Mugerero paddy soils is the main constraint to rice production, this process has not yet been investigated thoroughly. This work has been done to fill this gap. Physico-chemical analysis of soils of this area show that their exchange complex is mostly occupied by nearly equal percentages of Ca and Mg, while exchangeable sodium percentage vary up to 60% in some cases. Soil solution is characterized by large amount of sulfate or bicarbonate and sodium while chloride anion is poorly represented, and an alkaline pH. The Na - (Ca + Mg) exchange is well described either by a single Vanselow selectivity coefficient equal to 0.5 or by a single Gaines-Thomas selectivity coefficient equal to 0.3, while the Ca - Mg exchange is described by a single selectivity coefficient equal to 1.5. Moreover, analysis of correlations between yield components of rice and geochemical variables reveals positive effects of Ca and K ions on rice yield and negative effects of pH, salinity and / or soluble Na, SO4 or HCO3. The exploration of the cation contents of the soluble and exchangeable phases in five soil to water ratios shows that their variations as a function of water content are in conformity to the law of ion exchange and that the composition of solution and exchange phases for any moisture content can be estimated accurately from measurements carried out at 1/2 soil to water ratio using regression equations. Furthermore, incubation of the soil does not induce any important release of Fe and Mn in soil solution probably due to high values of pH. Moreover, potassium buffering capacity of these soils can be well predicted from clay content or sand content. Finally, soils of interest exhibit problems of salinity, sodicity and alkalinity that deserve to be keenly investigated for a best management in order to increase agricultural production., La salinisation des sols du périmètre rizicole de Mugerero, bien qu’elle soit la principale contrainte à la production rizicole, n’a pas encore fait l’objet de recherche approfondie. Ce travail a été effectué pour combler cette lacune. Les analyses physico-chimiques de ces sols montrent que le complexe d’échange est saturé par des taux de Ca et de Mg quasi-équivalents et des taux de Na variables jusqu’à 60%. La salinité est de type sulfaté ou bicarbonaté avec dominance du Na et faible part du Cl. La sélectivité du complexe d’échange pour le Na par rapport aux divalents (Ca+Mg) est bien décrite par une valeur unique du coefficient de sélectivité de Vanselow égale à 0,5 ou par une valeur unique du coefficient de sélectivité de Gaines et Thomas égale à 0,3. Quant à la sélectivité de l’échangeur pour le Ca par rapport au Mg, elle est bien décrite par une valeur unique du coefficient de sélectivité égale à 1,5. L’analyse des corrélations entre les composantes du rendement du riz et les variables pédochimiques révèle des effets positifs du Ca et du K sur le rendement rizicole et des effets négatifs du pH, de la salinité et/ou des ions solubles Na, SO4 ou HCO3. L’analyse des teneurs en cations solubles et échangeables à cinq rapports sol/eau montre que leurs variations en fonction de la dilution sont conformes à la loi des échanges ioniques et que les mesures faites à la dilution 1/2 peuvent servir au calcul des valeurs correspondantes à n’importe quelle dilution. Par ailleurs, l’engorgement des sols en anaérobiose n’est pas suivi de libération des cations Fe et Mn en raison des pH élevés. En outre, le pouvoir tampon vis-à-vis du K peut être bien prédit à partir du taux d’argile ou de sable. En définitive, les sols de Mugerero connaissent des problèmes de salinité, de sodicité et d’alcalinité qui méritent d’être profondément étudiés en vue d’une bonne production agricole., (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2014

Application of phosphorus (P) fertilizers to agricultural soils should be based on sound knowledge about soil P reserves, availability and lability to optimize conditions for plant uptake while limiting P transport to surface waters. This study investigated relationships between parent material (PM), land use and P fractions in agricultural soils at a regional scale. Surface and deep (100–120 cm) soil samples were collected from 120 agricultural sites (240 total samples) and analysed for three P forms (inorganic, organic and available) as well as for additional key properties. Land uses within the study area were continuous cropland, permanent pasture and temporary grassland. The area covered the 12 most common parent types in Wallonia. Mean total P contents were 904 and 401 mg/kg in surface and deep samples, respectively, with a 33% coefficient of variation for both horizons. The organic P fraction represented, on average, 30% of total P, while available P corresponded to 9% of total P. The influence of PM was apparent in both the surface and deep soil samples, while land use influenced only surface properties. The pattern in total P content relative to land use was pasture ≥ cropland ≥ temporary grassland. Correlation analyses highlighted significant relationships between edaphic parameters viz Alox, Feox, CEC, TOC, pH and P content, the main soil parameter being Alox which determines P sorption capacity. An enrichment factor was used to distinguish between geogenic sources and human activities in terms of topsoil P content.

Banana and coffee play a key role in Burundian agricultural production. But, coffee growing in monocropping system is less profitable. This pushes small producers to increase the area occupied by banana by planting banana around coffee plots or by intercropping coffee with banana. The aim of this thesis is to analyse the agronomic performance of banana-coffee intercropping system in order to recommend good management practices to sustain coffee production in Burundi. Using data from 60 adjunct coffee and banana plots, we observe that the growth and the yield of coffee are not affected by banana. Furthermore, the yield and the growth of banana are higher in banana close coffee. The buffer zone close coffee plots seems benefit to banana without negative effect on coffee. When banana is intercropped with young coffee, coffee yield and growth decrease by increasing banana density. On the other hand, cherry mean weight increase with density of banana. The effects of coffee on banana production and growth depend on coffee growing stage with negative effects with old coffee (7 years after stem pruning). Incomes are higher in plots with high density of banana whatever the age of coffee. This confirms the important place of banana in improving farmers’ living conditions. Banana-coffee intercropping could encourage small producers to invest in existing coffee plots or new coffee plantations. Optimizing the management of this system will avoid significant decrease of national coffee production., La banane et le café jouent un rôle important dans l’économie Burundaise. Mais, dans le système actuel de culture en pure, la caféiculture est moins rentable. Cela pousse les petits producteurs à accroître la part des bananiers en les plantant autour des parcelles de caféiers, voire en les associant avec les caféiers. Vu cette évolution, l’objectif de la thèse était d’étudier les performances agronomiques de l’association bananiers-caféiers en vue de pouvoir faire des recommandations pour une gestion durable des caféières. Sur base de l’analyse de 60 parcelles de bananiers et de caféiers adjacentes, on observe que le rendement et la croissance des caféiers ne sont pas affectés par la présence des bananiers. Cependant, le rendement et la croissance sont plus élevés chez les bananiers proches des caféiers. La zone tampon autour des parcelles de caféiers semble donc propice aux bananiers, sans effets néfastes sur les caféiers. Quand les bananiers sont associés avec des jeunes caféiers, le rendement de café et leur croissance diminuent avec l’augmentation de la densité des bananiers et le poids de 100 cerises augmente avec l’augmentation de la densité des bananiers. Les effets des caféiers en production sur les bananiers dépendent de leur stade de développement avec des effets négatifs uniquement quand les caféiers sont âgés. Les revenus sont plus élevés dans les parcelles avec forte densité de bananiers quel que soit l’âge des caféiers, confirmant le rôle central du bananier dans l’amélioration des conditions de vie des producteurs. L’association caféiers-bananiers pourrait inciter les petits producteurs à renouveler et à entretenir les caféières au Burundi. Une optimisation de la gestion de cette association est cependant indispensable pour qu’elle ne nuise pas outre mesure à la production nationale de café., (AGRO 3) -- UCL, 2013

Silicon is known to reduce the incidence of various pathogens on many plants. Banana is a Si-accumulator monocot plant. There is little information, however, about the potential positive effects of Si on the resistance of banana to plant pathogens. The objective of this PhD thesis was to determine the effects of Si supply on fungal infection on banana (Musa acuminata cv. Grande Naine). Experiments were conducted under controlled conditions in order to test the susceptibility of banana amended, or not, with Si to a root-rot fungus, Cylindroladium spathiphylli, and to a foliar pathogen, Mycosphaerella fijiensis. In the experiments, the Si supply led to an increase in the Si concentration in banana leaves, reaching values of 1% to 3%. Banana plants amended with 2mM Si on a ferralsol, exhibited a reduction of about 50% in the necrosis percentage of C. spathiphylli inoculated roots, 14 days after inoculation, compared with plants grown in the absence of Si. The Si amendment has a positive effect on plants affected by C. spathiphylli. The protective role of Si in the banana-M. fijiensis pathosystem was also highlighted in this work. The addition of Si to the nutrient solution supplied to plants resulted in a reduction and a delay of the disease progress. Biochemical analysis of leaf extracts of banana plants amended with Si and inoculated with M. fijiensis revealed a slightly higher concentration of total polyphenols and an increasing of the antioxidant activity compared to extracts from plants not amended with Si. These results suggest a relationship between the silicon supply, the total polyphenols content and antioxidant activity. The availability of silicon for banana plants was assessed in a sand-peat substrate amended with commercial wollastonite. The Si leaf concentrations increased with increasing rate of wollastonite amendment but remained relatively low in comparison with previous reports. These results show that calcium silicate with high rate could be a source, La banane représente une grande part des productions agricoles des pays tropicaux. Dans le contexte évolutif de la réglementation sur l’utilisation des produits phytosanitaires et dans la perspective de développer des systèmes de culture durables, il importe de concevoir de nouvelles stratégies pour lutter contre les maladies. Le silicium (Si) se révèle avoir un effet positif sur la résistance de plantes aux maladies. Le bananier étant une plante accumulatrice du Si, la question de l’effet protecteur du silicium sur cette culture méritait d’être posée. L’objectif principal de cette thèse a été d’évaluer si l’accumulation de Si chez le bananier (Musa acuminata cv. Grande Naine) s’accompagnait d’une meilleure résistance aux stress biotiques. Des essais en conditions contrôlées dans des systèmes de culture distincts ont été mis en place, afin de comparer la dynamique de progression du pathogène racinaire Cylindrocladium spathiphylli et du pathogène foliaire Mycosphaerella fijiensis selon le niveau d’amendement en Si. L’apport du Si sous forme d’acide silicique (1,7 à 2 mM) a permis une accumulation en Si dans les feuilles de bananier jusqu’à des teneurs de 1% à 3% du poids sec et a entraîné la réduction des dégâts causés par C. spathiphylli deux semaines après inoculation. Il a également permis d’augmenter le poids sec des racines saines des plantes inoculées. Une réduction de l’infection des feuilles par M. fijiensis et un retard du développement de la maladie associés à l’accumulation de Si dans les feuilles ont aussi été observés. Ces résultats révélaient l’intérêt tout particulier que peut représenter le Si dans la gestion intégrée des systèmes de production du bananier. La compréhension du mode d’action du Si dans la résistance du bananier aux stress biotiques a été abordée au travers de l’analyse biochimique d’extraits de feuilles inoculées par M. fijiensis. Une augmentation de la teneur en polyphénols totaux et de l’activité antioxydante en présence de silicium, (AGRO 3) -- UCL, 2012

Zinc (Zn) sorption curves were established for 11 cultivated sandy soils from central Vietnam. Soil samples (10 g) were equilibrated with 5 mM calcium chloride (CaCl 2) solutions (50 mL) at five zinc chloride (ZnCl 2) concentrations (0 to 80 mg Zn L -1). The experimental sorption data were fitted with the Freundlich equation. The amounts of Zn sorbed by soil (Q Zn) at different Zn concentrations in the equilibrium solution (C Zn) were closely related to cation exchange capacity (CEC) and pH, that is, to the available exchange sites at given pH values. More specifically, an excellent correlation was found between Zn sorption and exchangeable calcium (Ca ex), which evidently also depends on CEC and pH. A unique equation was proposed to predict Q Zn from C Zn and Ca ex in the range of Zn loading covered in our research, that is, from traces to Q Zn ≈ 60 mg Zn kg -1. © 2012 Copyright Taylor and Francis Group, LLC.

Banana is a crop of major importance in the African Great Lakes Region, because of the food and cash it provides to about 85% of the population. Despite the management efforts of smallholder farmers, on-farm banana yields are low. Low yields are mainly attributed to poor soil fertility and limited input use, drought or irregular rainfall, pests and diseases and inappropriate management practices. Relying on observations on banana plants, crop management, pests and soils in various agro-ecoregions in Rwanda and South-West Uganda, this PhD-thesis contributes to the understanding of the traditional banana-based systems by (1) ranking constraints and quantifying associated yield losses, (2) evaluating the temporal and spatial variations of soil nutrient pools, (3) relating soil fertility to the mineralogical and organic components of the soil. Hence, a Boundary Line Analysis on the available data shows that the gap between actual production and attainable yield may attain 70-96% and that poor soil fertility is an overall problem in the Great Lakes Region. Further analysis of plant foliar data highlights associated nutritional disorders. Banana production does not only vary at regional scale in function of soils and parent materials, but also changes at inter-regional or intra-farm level. Within-farm differences may relate to differential management of organic matter. In order to assess the human imprint on soil fertility, organic matter and soil minerals are evaluated as nutrient providers and as contributors to the cation exchange capacity of the soil. These analyses quantify soil mineral abundances and emphasize the key role of organic matter in maintaining soil fertility., (AGRO 3) -- UCL, 2011