Effect of organic and inorganic fertilizers on regeneration of seedlings of Ricinodendron heudelotii (Baill) Pierre et Pax.

Most soils in the humid tropical zones present a particular problem. Due to leaching, the fertilizer provided by the process of nutrient cycling in tropical rainforest is confined to the top few inches of the soil. Varying quantities of manure and NPK fertilizers were applied to assess their effects on the growth of Ricinodendron heudelotii seedlings, a non-timber-forest-product. Assessment was done by measurements of height, number of leaves, leaf area, seedling biomass, the relative growth rate, and the net assimilation rate. The effects of organic and inorganic fertilizers on plant height and number of leaves were not significant, though their effect on leaf area was significant (p<0.05). The total biomass, relative growth rate, and net assimilation rate under the different treatment combinations had no significant effect on yield. However, fertilizer treatments had a significant effect among the periods of application for the biomass and the net assimilation rate (p<0.05), but had no significant effect on the observation period for the relative growth rate.Keywords: Manure, NPK, non-timber-forest-product, biomass, relative growth rate, net assimilation rate

Litter decomposition and nutrient dynamics of ten selected tree species in tropical rainforest of Ebom, southwest Cameroon

Litter decomposition processes in tropical rainforests are still poorly understood. Leaf litter decomposition and nutrient dynamics of ten contrasting tree species, Entandraphragma utile, Guibourtia tessmannii, Klainedoxa gabonensis, Musanga cecropioides, Panda oleosa, Plagiostyles africana, Pterocarpus soyauxii, Strombosia scheffleri, Vitex grandifolia and Xylopia aethiopica were studied in the tropical rainforest of Ebom, Southwest Cameroon. After 23 weeks of field incubation in litterbags, mass loss of litter samples varied from 24.08% in E. utile to 92.35% in V. grandifolia. Decomposition rate constants (k) ranged from 0.014 in M. cecropioides to 0.165 week-1 in V. grandifolia. The nutrient content in original litter samples also varied widely among species and showed low levels of Na, P and Mg, and high levels of N, Ca and K. Averagenutrient releases was 89.04%, 60.80%, 46.19%, 40.99% and 24.17% of mean initial content for K, Ca, Mg, N and P, respectively. For nutrient-related litter chemistry, correlations with the mass losses at the end of litter incubation were significant (

Disentangling the pedogenic factors controlling active Al and Fe concentrations in soils of the Cameroon volcanic line

Active Al, Fe and Si (i.e., oxalate extractable fraction: Alo, Feo, Sio) strongly affect soil physical, chemical and biological properties. This study examined the pedogenic factors affecting Alo, Feo and Sio contents across a soil weathering sequence in the Cameroon volcanic line. We investigated the B horizon (∼50-cm depth) from 26 soils formed in basaltic materials at different elevations (110–2570 m) incorporating a wide range of temperature (14–27 °C) and precipitation (1520–3130 mm). The weathering sequence ranged from weakly weathered Andisols in the southwest region grading to strongly weathered Oxisols on the central highlands. We assumed pyrophosphate extractable Al/Fe (Alp/Fep) as organo-Al/Fe complexes, and Sio, (Alo − Alp) and (Feo − Fep) as short-range-order (SRO) minerals. Factor analysis of climatic (e.g., temperature and precipitation/leaching metrics) and soil geochemical properties (e.g., weathering indices) identified three independent factors representing temperature/dry season intensity, weathering degree and precipitation/leaching as the primary determinants of Alo, Feo and Sio concentrations. Organo-metal complexes (Alp and Fep) were negatively correlated with the temperature/dry season intensity factor, whereas the SRO mineral phases (Sio, Alo − Alp and Feo − Fep) were negatively correlated with weathering degree. The precipitation/leaching factor positively correlated with Alo, Feo and Sio. Our analysis infers that low temperature promotes the formation and preservation of organo-Al/Fe complexes, whereas weathering degree is more critical for SRO minerals. Further, increased weathering and a drier climate enhance the formation of crystalline clay minerals at the expense of SRO minerals. Allophanic materials (Sio) were evident (Sio: 9–43 g kg⁻¹) only in weakly weathered soils. However, low allophanic contents were found in more highly weathered soils (Sio: 2–7 g kg⁻¹) accompanied by high Alp and Fep, suggesting the importance of volcanic parent materials as a direct source of Al and Fe via weathering for the formation of organo-metal complexes. In sum, we clarified the discriminatory effects of climatic factors and degree of weathering in regulating the composition of the active Al, Fe and Si fractions along the Cameroon volcanic line

Above-ground biomass and nutrient accumulation in the tropical rainforests of southern Cameroon: effects of logging

Impact of logging activities on nutrient cycling in tropical rainforests of southern Cameroon has been little investigated. A study was initiated by the Tropenbos-Cameroon Programme to determine changes in above-ground phytomass and nutrient stock following selective logging in Ebom rainforest of Southern Cameroon. One hundred and twelve (112) trees were sampled in three undisturbed plots of 10m x10m. Their diameters and dry mass were determined. Allometric equations (Y = a + b*D + c*D2 and Y = a’*D b’ ), relating dry mass of foliage, branches, trunks with barks, and total biomass to diameter at breast height (DBH), were developed to estimate the above-ground tree biomass of undisturbed anddisturbed forests. Understorey biomass was estimated by harvesting method. The total above-ground tree biomass is about 583 t.ha-1dry mass in the undisturbed forest. This contains 302 t.ha-1 C and a nutrient capital of 8888 kg.ha-1N, 6953 Ca, 2337 K, 436 P, 311 Mg and 30 kg. ha-1 Na. The stores of nutrient in the above-ground biomass was about 2 (311 and 175 kg ha-1) to 16 (436 and 28 kg. ha-1) times higher than in the top soil stock, respectively for Mg and available P. The losses of carbon and nutrients associated with timber extraction represented less than 7% of store in the above-ground biomass for all nutrients. This means that the impact of logging in the Ebom rainforest remains low. However, additional research is needed on nutrient input in the forest from outside as well as on the impact of logging on nutrient leaching in order to get a complete picture of the nutrient cycles.Key-words: phytomass, nutrient pools, logging, allometric equations, tropical rainforest, Southern Cameroo

Some chemical characteristics of selected geological materials in Cameroon (Central Africa) and their potential use for crop production.

This study was carried out in order to characterize some selected local geological materials so as to prove their potential use for crop production. For this purpose, two types of volcanic breccias, volcanic ash and marl from West Cameroon region were selected for chemical characterization. These chemical analyses were done in order to determine total concentrations, extractible fractions, the readily available fractions and water-soluble fractions of nutrients. The results showed that all materials tested were alkaline to neutral (pH = 9.04 to 6.79), with significant difference (p < 0.05) in values from breccias 3 to volcanic ash. Concentrations of macronutrients (N, P, K, Mg, Ca, and C) and micronutrients (Cu, Zn, and Mn) and their availability were consistent with those reported in the literature. These materials contain acid–extractable fractions (5.3 to 61.3% of Ca; 0.6 to 10.5% of Mg; 8.5 to 49.95% of K; 2.59 to 95.6% of P and 0.07 to 3.7% of Na), readily available fractions complexed by ammonium acetate (5.14 to 32.76% of Ca; 0.06 to 9.09% of Mg; 7.52 to 35.9% of K; 0.84 to 3.33% of K and 0.00 to 0.04% of Na), and water soluble fractions (0.04 to 0.78% of Ca; 0.10 to 0.36% of Mg; 1.02 to 1.3% of K; 0.01 to 0.88% of Na and 0.09 to 1.04% of P) of some elements. K and Ca appear to be the most ready available elements in most samples (p < 0.05)) followed by Mg and Na (p < 0.05). Breccias gave the highest release of Ca, Mg, K, and Na, but a low release of P in water. Nutrients were less soluble in the volcanic ash. K appears to be the most water-soluble element in all the materials. The amounts of nutrients released during the kinetic study (50 to 91% during the first 30 minutes of shaking) were comparable and/or higher in some cases than those obtained in most agrogeological materials in the world. These materials, highly concentrated in macro and micronutrients required for plant growth and easily releasable, are likely to add nutrients to the soil. Keywords: Agrogeological materials, Cameroon, macronutrients, micronutrients, chemical extraction.International Journal of Biological and Chemical Sciences Vol. 2 (1) 2008 pp. 21-3

Etude de la désorption des éléments nutritifs de certains matériaux agrogéologiques du Cameroun

Un essai d’équilibration et une étude de la désorption en quatre semaines par la méthode de Snoek des éléments minéraux des marnes de Kompina, des cendres volcaniques de Foumbot et des brèches volcaniques de Fongo-Tongo, ont été initiés dans l’objectif de pouvoir estimer les vitesses de libération des éléments dans le sol afin de pouvoir déterminer les périodes d’épandage des poudres de roches par rapport aux semis. Lors de l’équilibration des cendres, les éléments majeurs ont été libérés plus rapidement, comparées aux autres roches, pendant les deux premières semaines et ensuite la désorption a été progressive les deux dernières semaines. La libération des éléments nutritifs par les différentes roches est dans l’ensemble proportionnelle au temps avec des libérations maximales à la deuxième semaine, et inversement proportionnelle aux doses avec des libérations plus importantes pour les doses inférieures à 2.28 t/ha. La variation du pHeau dans le sol croît en fonction du temps et des doses pour les trois types de roches alors que celle du pHkcl montre une croissance assez nette seulement pour les marnes. L’altération des trois roches étudiées a été étalée sur les quatre semaines de l’observation avec une grande aptitude des brèches à être utilisées comme fertilisant dans les systèmes diversifiés (apport d’un flux élevé en P et Ca), les marnes pouvant être recommandées pour les cultures à cycle court puisque les éléments sont assez vite libérés à la première semaine.© 2010 International Formulae Group. All rights reserved.Mots clés : Matériaux agro-géologiques, essai d’équilibration, libération progressive, re-minéralisation,potentiel fertilisant

Production de biomasse de Brachiaria ruziziensis (Germain et Evrard) en vue de la mise en place de systèmes de culture sous couvertures végétales dans la zone cotonnière du Cameroun

R&#233;sum&#233; Les syst&#232;mes de culture sous couvertures v&#233;g&#233;tales vulgaris&#233;s dans la zone cotonni&#232;re du Nord Cameroun reposent sur la production en premi&#232;re ann&#233;e de fortes biomasses sur lesquelles sont install&#233;es les cultures subs&#233;quentes. La pr&#233;sente &#233;tude avait pour objectif d&#8217;&#233;valuer la production de biomasse de l&#8217;esp&#232;ce Brachiaria ruziziensis en t&#234;te de rotation dans les syst&#232;mes de culture de la zone cotonni&#232;re du Cameroun, en pr&#233;sence des fumures organique et min&#233;rale recommand&#233;es. La production moyenne de biomasse de l&#8217;esp&#232;ce B. ruziziensis a &#233;t&#233; significativement diff&#233;rente entre les sites de Guiring, Djalingo et Touboro au Nord, au Centre et au Sud de la zone cotonni&#232;re, respectivement. Le site de Touboro a &#233;t&#233; le plus productif (20,2 t MS ha-1), suivi de Guiring (11,7&#160; t MS ha-1) et Djalingo (8,6&#160; t MS ha-1). Les quantit&#233;s de biomasse ainsi obtenues sont suffisantes pour l&#8217;installation des syst&#232;mes de culture sous couverture v&#233;g&#233;tale l&#8217;ann&#233;e subs&#233;quente. Les diff&#233;rences observ&#233;es entre les sites recommandent une &#233;valuation de leur potentiel de production de biomasse avant la mise en place des syst&#232;mes de culture vulgaris&#233;s. La fertilisation recommand&#233;e devrait &#234;tre maintenue, bien qu&#8217;elle soit g&#233;n&#233;rale pour l&#8217;ensemble des gramin&#233;es, en attendant que des essais pour la d&#233;termination des doses optimales utilisant une gamme plus &#233;tendue de nutriments soient effectu&#233;s. Mots cl&#233;s: Agriculture de conservation, Plante de couverture, Brachiaria ruziziensis, &#160;biomasse. &#160; Abstract Direct seeding mulch-based cropping systems that have been recently introduced in Northern Cameroon recommend sowing cover crops in the first year of rotations which are followed by subsequent crops of interest. The objective of this study was to evaluate the seeding year biomass production of Brachiaria ruziziensis in the cotton producing zone of Cameroon, under recommended organic and mineral fertilizer rates. Biomass production of B. ruziziensis was significantly different among the experimental sites. The highest dry matter yield was recorded in Touboro (20.2 t DM ha-1), followed by Guiring (11.7 t DM ha-1) and Djalingo (8.6 t DM ha-1), stations located to the South, North and Centre of the cotton production zone, respectively. These biomasses are enough for the implementation of direct seeding mulch-based cropping systems. The differences observed among sites suggest their evaluation for biomass production before the use of such systems. Though common to all grasses, the present fertilizer recommendations should be maintained but further work is needed for the determination of optimal fertilizer recommendations using a more extended nutrient scale. Key words: Conservation agriculture, Cover crop, Brachiaria ruziziensis, biomass

Impact des légumineuses fourragères et/ou de couverture sur la biodiversité floristique au Nord-Cameroun.

Une étude synchronique a été menée dans un dispositif expérimental mis en place en juin 1994 en zone soudano-sahélienne du Cameroun et comprenant quatre types de jachères améliorées avec des légumineuses à usages multiples. Initialement conçu pour mesurer l'impact de la coupe et de la pâture sur le rendement grainier de Calopogonium mucunoides, Stylosanthes hamata, et Cajanus cajan, ce dispositif a été laissé en jachère de 1995 à mai 2000. L'évolution de la flore et de la production de biomasse herbacée 6 ans après abandon ont été étudiées en utilisant la méthode phytosociologique sigmatiste et l'analyse structurale par la méthode des points quadrats. L'analyse de la production de biomasse a été faite par la méthode des coupes totales. Les résultats obtenus montrent que les légumineuses utilisées permettent une augmentation significative de la biomasse herbacée des jachères. Par leur aptitude à coloniser rapidement l'espace, elles concourent à l'appauvrissement de la biodiversité floristique. Ce caractère nettoyant peut être utilisé pour lutter contre la persistance des adventices dans les parcelles agricoles. La litière accumulée est plus importante dans les jachères à Calopogonium mucunoides, et dans celles ayant comme antécédent l'association Cajanus cajan / Zea mays. Des analyses ultérieures permettront de mettre en évidence l'impact de ces légumineuses sur la fertilité des sols de la région.International Journal of Biological & Chemical Sciences Vol. 1 (2) 2007: pp. 165-17