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.