Arenosols cover extensive areas in coffee producing, humid tropical countries of Sub-Sahara Africa (Angola, DR Congo) and Southern America (Brazil). A laboratory experiment was undertaken to examine the potential of using coffee waste to improve the physico-chemical properties of an Arenosol from DR Congo. The amendment was applied at three rates to the topsoil and incubated in soil columns at field moisture capacity for 24 months. A control without any amendment was integral to the completely randomized experimental design involving three replicates. The soil columns were watered weekly with an amount of distilled water approximating to 87% of the average rainfall. Every 3 months, the soil chemical properties and the fraction of leached water and cations were measured. All application rates raised soil pH above 5.5 within 3 months. Exchangeable Ca, Mg and K showed respectively, 5 to 7-, 2 to 3-and 7 to 14-fold increases with increasing application rates. Organic C and total N significantly increased within 6 months to ca. 1.5 and 0.12% respectively, inducing a decrease in the C ⁄ N ratio from 17 to 13. The combined action of increasing soil pH and organic C contributed to a significant increase in cation exchange capacity. Increases in available P were significant, but temporary, with maximum values attained at 9 months. Coffee waste application significantly increased the fraction of retained soil water from 53% to 60%. It promoted the retention of basic cations, immobilized Mn, but increased the mobility of Fe. Coffee waste has the potential to be used as a liming material, an NPK fertilizer and has the benefits also of increasing water and nutrient retention.Coffee waste application to improve sandy soils 95

A 17‐year chronosequence of Acacia auriculiformis fallows on Arenosols of the Batéké Plateau (D.R. Congo) was surveyed and compared with virgin savannah soils to assess chemical soil fertility changes induced by these N‐fixing trees. Significant increases in organic carbon content, total nitrogen content, cation exchange capacity and sum of base cations were found after relatively short fallow periods of only 4 years and did not only affect the forest floor, but extended to at least 50 cm depth. The Acacia act as a major source of organic matter (OM), hence increasing organic carbon and nitrogen content and decreasing the C/N ratio. The increased OM content suggests that humification processes are the main cause of the significant decrease in pH. Total exchangeable cations initially increased slowly but doubled (topsoil 0–25 cm) and tripled (subsoil 25–50 cm) after 10 years. The point of zero net proton charge was systematically lower than soil pH and decreased with increasing OM content, thereby increasing the cation exchange capacity, although concurrent acidification retarded a significant beneficial impact at field pH on Acacia fallows of 10 years and older. Although the chemical soil fertility improves steadily with time, after 8 years of Acacia fallow the absolute amounts of available nutrients are still small and slash and burn practices are required to liberate the nutrients stored in the remaining biomass and litter before each new cropping period.

A greenhouse experiment was conducted to study the effect of coffee waste (CW) application on growth and mineral nutrition of Italian ryegrass in a tropical Arenosol. Dry CW was applied at three rates (5, 10, 20 t/ha) and thoroughly mixed with topsoil (0-25 cm), placed in pots and seeded with Italian ryegrass (Lolium multiflorum Lam.) according to a completely randomized design with six replicates. The application of CW greatly stimulated uptake of Ca, Mg, K, N and P, resulting in a significantly increased dry matter (DM) production over three consecutive cropping cycles. DM increases of at least 52, 87 and 81% compared with the unamended controls were obtained for the first, second and third cuts, respectively. Soil analysis after cultivation found that all CW-amended soils still contained available macronutrients (Ca, Mg, K, N), which could produce residual effects in subsequent crops. Furthermore, CW application increased soil pH owing to its liming effect. This brought about an increase in cation exchange capacity with substantial reduction in phytotoxic Al and a decrease in availability of a number of metals (Cu, Zn, Mn and Fe) and significantly reduced their uptake by ryegrass. The study reveals a high potential of CW to improve the fertility of sandy soils in the humid tropics.

The sandy soil from Kinshasa's hinterland (DR Congo) is characterized by a low chemical fertility, a very limited water retention capacity, and an acidic pH with Al and Mn toxicities. The effects of Kanzi rock phosphate (PK) and Kimpese pink dolomite (DK) application on soybean (dry matter weight content, nodulation, and soybean grain yield) and chemical soil properties after cultivation were studied. Four rates of finely ground rocks (0, 199, 397 and 794 mg PK, and 0, 437, 874 and 1748 mg DK kg soil(-1)) were mixed with the topsoil, and soybean (Glycine max) was planted using a completely randomized design with three replicates. The application of PK and DK stimulated the absorption of nutrients (Ca, Mg, K and P) and increased significantly the nodulation, dry matter weight content and soybean grain yield. Application of 2.48 Mg ha(-1) PK and 5.46 Mg ha(-1) DK increased dry matter content by 112 and 191%, respectively, and seed weight by 86 and 197%, respectively. Soil analysis after cultivation illustrated that all amended soils still contained nutrients (Ca, Mg, N and P) which could produce long-term beneficial effects. Furthermore, the increased soil pH, due to the liming effect of the amendments brought about a significant increase in CEC with complete neutralization of phytotoxic exchangeable Al. The study demonstrates that the significant decrease in solubility of micronutrients (Cu, Zn, Mn and Fe) significantly reduced their absorption by plants. Kanzi rock phosphate and Kimpese pink dolomite have the potential to increase the productivity of tropical soils

Effet in vitro de la roche verte de Gangila sur les proprie´te´s physico-chimiques des sols sableux de l'hinterland de Kinshasa (RD Congo). Can. J. Soil Sci. 92: 787Á797. Les roches vertes de Gangila (Bas-Congo), sont constitue´es principalement d'amphibolites et de schistes verts et ont un grand potentiel en nutriments. Une e´tude in vitro a e´te´conduite pour e´tudier les effets d'application de ces roches comme fertilisants sur diverses proprie´te´s physico-chimiques des sols sableux de l'hinterland de Kinshasa, RD Congo. Ces sols, classifie´s comme Orthic Re´gosols selon le syste`me Canadien de classification des sols (Are´nosols en WRB), sont caracte´rise´s par une faible fertilite´chimique, une capacite´de re´tention en eau tre`s limite´e, et une re´action acide susceptible d'induire une toxicite´aluminique, voire manganique, pour les cultures. Quatre doses correspondant a`0,0 ; 12,5 ; 25,0 et 50,0 Mg ha (1 de roche finement broye´e ont e´te´me´lange´es avec des sols de surface (0Á25 cm), puis incube´es et lessive´es pendant 3, 6, 9, 12, 15 et 18 mois. L'apport de la roche verte de Gangila au sol accroıˆt significativement le pH (5,5), la disponibilite´en P, la somme des cations basiques (SCB), la CEC, et augmente d'environ 3 % (volume) la capacited e re´tention d'eau dans les sols. Des augmentations allant jusqu'a`50 % P extractible, 2,2 cmol c kg (1 SCB et 75 % CEC ont e´te´enregistre´es dans les sols amende´s de 50,0 Mg ha (1 apre`s 6 mois d'incubation. Par ailleurs, l'accroissement du pH et la re´duction du pH 0 (point de charge ze´ro) due a`l'adsorption des ions silicates ont produit une augmentation significative des charges ne´gatives CEC B (capacite´d'e´change cationique basique) et CEC T (capacite´d'e´change cationique totale) avec une neutralisation comple`te de la phytotoxicite´aluminique (pH-H 2 O 5,5). L'e´tude du percolat a re´ve´le´que l'application de roches vertes de Gangila finement broye´es influence sensiblement la dynamique des cations et immobilise certains microe´le´ments (Fe, Cu, Mn, Zn). La perte relative des cations monovalents (K ' , Na ') a e´te´plus importante que celle des ions bivalents (Ca '' , Mg ''). Les roches vertes de Gangila peuvent servir d'amendements naturels pour augmenter la fertilite´des sols sableux tropicaux.

In tropical Africa, a productive and sustainable agricultural system is one of the fundamental priorities to the well-being and food safety of the population, and it constitutes a cornerstone of development. The fast growing African population and the continued soil fertility degradation require special management practices for sustaining agricultural productivity over a long period of time. This is of particular importance to the province of Kinshasa (DR Congo), where the sandy soils covering the major part ofits hinterlands are very marginal and severely constraining the food supply to the capital. Furthermore, the farmers and local population have only limited capital at their disposal and therefore cannot afford regular applications of conventional chemically processed fertilizers. The use oflocal geological resources (agrominerals, rock fertilizers or petrofertilizers) and organic industrial wastes in the crop production systems can be an alternative solution to enhance soil productivity.This study has been conducted within the frame of research for appropriate methods of sustainable management of the sandy soils of Kinshasa's hinterland, in order to ensure and guarantee the food security. It consists of scientific research of the use of greens tone of Gangila, pink dolomite of Kimpese, rock phosphate of Kanzi and coffee waste to improve the quality of the sandy soils on the Bateke plateau, being the eastern part of Kinshasa's hinterland. The study comprises 7 different chapters. The first two chapters are devoted to the physical environment of the Bateke plateau and to a literature review on the use of agrominerals and industrial coffee wastes in agriculture, as well as to the theoretical concepts used to describe surface charges of highly weathered, tropical soils. The 5 last chapters deal, respectively, with the agropedological status of the soils, the impact assessment of Acacia auricullformis forest on the chemical fertility of soils, the characterization of the amendments, the reactions of these amendments with the soils, and their effects on plant growth and mineral nutrition.The determination of the agropedological status of the soils showed that the Bateke sandy soils, classified as Rubie Ferralic Arenosols (Dystric) in WRB (FAO, 2006), and as Isohyperthermic Ustoxique Quartzipsamments according to USDA Soil Taxonomy (Soil Survey Staff, 2006), have a clayey mineralogy limited to kaolinite and residual oxides of Al and Ti. These soils are dominated by variable charge colloids; they present an acid reaction with Al and Mn toxicities, and have low organic matter and mineral nutrient contents.

No abstract

In tropical Africa, a productive and sustainable agricultural system is one of the fundamental priorities to the well-being and food safety of the population, and it constitutes a cornerstone of development. The fast growing African population and the continued soil fertility degradation require special management practices for sustaining agricultural productivity over a long period of time. This is of particular importance to the province of Kinshasa (DR Congo), where the sandy soils covering the major part ofits hinterlands are very marginal and severely constraining the food supply to the capital. Furthermore, the farmers and local population have only limited capital at their disposal and therefore cannot afford regular applications of conventional chemically processed fertilizers. The use oflocal geological resources (agrominerals, rock fertilizers or petrofertilizers) and organic industrial wastes in the crop production systems can be an alternative solution to enhance soil productivity.This study has been conducted within the frame of research for appropriate methods of sustainable management of the sandy soils of Kinshasa's hinterland, in order to ensure and guarantee the food security. It consists of scientific research of the use of greens tone of Gangila, pink dolomite of Kimpese, rock phosphate of Kanzi and coffee waste to improve the quality of the sandy soils on the Bateke plateau, being the eastern part of Kinshasa's hinterland. The study comprises 7 different chapters. The first two chapters are devoted to the physical environment of the Bateke plateau and to a literature review on the use of agrominerals and industrial coffee wastes in agriculture, as well as to the theoretical concepts used to describe surface charges of highly weathered, tropical soils. The 5 last chapters deal, respectively, with the agropedological status of the soils, the impact assessment of Acacia auricullformis forest on the chemical fertility of soils, the characterization of the amendments, the reactions of these amendments with the soils, and their effects on plant growth and mineral nutrition.The determination of the agropedological status of the soils showed that the Bateke sandy soils, classified as Rubie Ferralic Arenosols (Dystric) in WRB (FAO, 2006), and as Isohyperthermic Ustoxique Quartzipsamments according to USDA Soil Taxonomy (Soil Survey Staff, 2006), have a clayey mineralogy limited to kaolinite and residual oxides of Al and Ti. These soils are dominated by variable charge colloids; they present an acid reaction with Al and Mn toxicities, and have low organic matter and mineral nutrient contents.