Pay Drechsel

Foliar nutrient levels of broad-leaved tropical trees: A tabular review

Foliar nutrient levels (N, P, S, K, Ca, Mg, Al, Fe, Mn, Zn, Cu, Mo, B), of about 40 tropical and subtropical broad-leaved trees, are listed and classified as deficient, low, intermediate, high, and toxic in each case according to the interpretation and evaluation of the reviewed author(s).

A review on the potential of improved fallows and green manure in Rwanda

Agricultural production in the densely populated highlands of Rwanda is subject to serious soil fertility constraints. As the use of imported mineral fertilizers is beyond the economic means of resource-poor farmers, research and extension efforts of several projects, institutes and organizations concentrated during the last 15 years on the development and promotion of improved fallows with woody and herbaceous legumes, like Tephrosia sp., Cajanus sp., Crotalaria sp., Sesbania sp., Mucuna sp., and Mimosa sp., planted over one or more seasons as pure green manure, in hedgerows (alley cropping), or on fields as seasonal inter- or relay-crop.Green manuring proved to be a risky enterprise, due to highly variable biomass production and residual effects. Yield increments on-farm of up to 74% in the first season and 46% in the second season did not compensate loss of yields and labour investments during green manuring. Even where biomass production was sufficient, residual effects were in most cases unsatisfactory, due to rapid nutrient leaching (N, K) or inappropriate foliage incorporation on-farm. In researcher-managed trials, residual effects were in general somewhat higher, but more than a mere compensation of lost yields was not possible and farmers adoption of these labour-intensive technologies was rather low. Due to acute land shortage, farmers were reluctant in allocating land to fallows or hedgerows also, with the exception of fields already out of production. Consequently, the concept of improving soil fertility and crop yields with the help of planted fallows or green manure in rotation failed. Woody legumes might have a future on abandoned fields and in wide spaced contour hedges, mainly for the production of firewood and bean stakes. For soil fertility management, the production and availability of farmyard manure and country-own mineral fertilizers, such as travertin and volcanic ashes should be supported. The question is raised as to whether sustainable agricultural development is possible without a credit system for small farmers, reallocating land and creating off-farm employment.

Effect of four multipurpose tree species on soil amelioration during tree fallow in Central Togo

The effects of Cassia siamea, Albizia lebbek, Acacia auriculiformis, and Azadirachta indica on soil fertility have been studied on five-year-old fallows on Ferric Acrisols in Central Togo. Litter quality and soil fertility under the four species were significantly different. Topsoil pH increases significantly with increasing litter Ca levels. Cassia siamea and Azadirachta indica were superior in enriching the sandy-loamy topsoils with Calcium and in increasing soil pH. Under Acacia, which had the highest biomass production, litter accumulation appeared to be responsible for the low mineral soil Ca and P values. In addition, topsoil pH under Acacia was lower than under grass or bush fallow or the other species. Slow litter mineralization of Acacia auriculiformis was probably caused by the thick, leathery consistence and high tannin content of its litter. Due to its high biomass production supporting soil acidification pure Acacia auriculiformis stands seemed to be less favourable for improving soil fertility on planted fallows but more suited for firewood plantations and topsoil protection. The foliage as well as the litter and topsoil under Albizia showed narrow C/N- and C/P-ratios resulting in easily mineralizable organic matter. All tree species tested were superior to natural grass/herb fallow in building up surface soil fertility. However, differences with natural bush fallow were not significant.RésuméAu bout de cinq ans des differences fortement significative ont été trouvées quant aux caractères de la litière et de la fertilité des jachères arborées avec Cassia siamea, Albizia lebbek, Acacia auriculiformis et Azadirachta indica, respectivement. ll y a une corrélation positive entre le pH de lhorizon superficiel et la teneur en Ca dans la litière: lenrichissement du sol sable-limoneux en Ca et le pH sont plus élevés sous Cassia siamea et Azadirachta indica que sous les autres espèces. Acacia se caractérise par la plus grande production en biomasse, donc une accumulation importante de litière sur le sol, ce qui entraîne les plus faibles teneurs en P et Ca dans lhorizon de surface. En plus, il semble quelle fait diminuer le pH parce que les valeurs trouvées sont inférieures à celles des parcelles témoin ou des autres espèces. La mineralisation retardée de la litière de Acacia auriculiformis depend probablement de la consistence des feuilles et du content élevé de tannine. Acacia est par consequent moins favorable à des jachères plantées mais plutôt efficace quant à la production du bois de feu et la protection du sol contre lérosion. Vu les petits rapport C/N et C/P dans les feuilles, la litière et dans lhorizon superficiel dAlbizia, on peut supposer que sa matière organique soit plus facilement décomposable. Toutes les espèces darbre étudiées sont plus capables de lever la fertilité des sols que les herbes des parcelles témoin. La comparaison avec une jachère spontanée darbustes ne fait pas apparâitre deffets significatifs.

Relationships between growth, mineral nutrition and site factors of teak (Tectona grandis) plantations in the rainforest zone of Liberia

Abstract In 5–11-year old teak plantations at Glaro, Cavalla and Bomi Hills in Liberia, growth and vigour of trees show considerable variations. Deficiency symptoms as well as soil and plant analyses indicate that differences in growth intensity are mainly related to topsoil acidity and foliar calcium status. Calcium deficiency seems to be caused by low soil reserves in highly weathered soils as well as by reduced uptake caused by root growth inhibition at waterlogged sites. Additionally, there are mineral disorders concerning the nitrogen, phosphorus and manganese supplies of teak.

DRIS evaluation of teak (Tectona grandis L.f.) mineral nutrition and effects of nutrition and site quality on teak growth in West Africa

Abstract The objective of the investigation was to study the site variables controlling teak yield ( Tectona grandis Linn.fil.) and to establish guidelines for the selection of high productivity sites in Benin, Cote dIvoire, Liberia, Nigeria and Togo. Depending on stand age, soil and region, between 70 and 90% of the variation in tree growth (site index, SI ) could be explained by the supply of nitrogen, the root-available soil depth and precipitation. Diagnostic foliar analysis for a broad range of elements was carried out in all plantations with the exception of Nigeria. This showed that in 20% of the stands, various deficiency symptoms occur, and in an additional 40%, hidden demand of at least one nutrient is apparent. According to the Diagnosis and Recommendation Integrated System (DRIS), the most deficient nutrients besides N are Ca and P, while in 45% of all stands there is a relative Al excess. Recommendations for the evaluation and classification of site quality and the number of trees sampled for foliar analysis are given.

Multiple mineral deficiencies in forest plantations in Liberia

Abstract Mineral deficiencies are often responsible for growth abnormalities, growth inhibition and the decline of tree plantations in the rain forest zone of Liberia. Foliar analyses of Pinus caribaea, P. oocarpa and several exotic as well as native broad-leaved species show obvious differences in the nutrient status of fast-growing, healthy trees and slowly growing trees with deficiency symptoms. Besides phosphorus, foliar levels of potassium, magnesium, and nitrogen seem to be below the critical range in pines. On the other hand, high aluminium and iron concentrations occur frequently.

The synergism between SO2 oxidation and manganese leaching on spruce needles — A chamber experiment

Four year old spruce (Picea abies (L.) Karst.) seedlings were planted in sand pots and supplied with nutrient solution. Three groups were formed, differing only in manganese nutrition (0.5 ppm, 2.5 ppm, 12.5 ppm, respectively). After three months, five individuals of each group were transferred to a dew chamber. For the next seven weeks the trees were sprayed in the evenings, the relative humidity overnight was kept high and the droplets were collected directly from the needles in the mornings. The trees were sprayed with HNO3 (pH 3.4) during the first three weeks to reduce the natural buffering capacity of the needles. After this time, the trees were sprayed with KCl (1 mM) solution, and NaHSO3 was added to the chamber resulting in SO2 concentrations usually between 50 and 150 microg m(-3). Needles and water samples were analysed. Foliar Ca seemed to be only a short-time buffer even under optimal Ca supply. A highly significant influence of managanese supply on manganese in needles and droplets was observed, as well as on sulphate, H+ and calcium concentrations in the droplets. The SO2 flux to trees treated with 12.5 ppm Mn was about twice as high as to trees treated with 0.5 ppm Mn. The conclusion is that this is due to a synergism between manganese leaching and catalysis of the SO2 oxidation by the leached Mn2+ ions. The results suggest a positive feedback between (moderate) acidification of soils and SO2 and NH3 inputs to terrestrial ecosystems.

Site conditions and nutrient status ofCordeauxia edulis (Caesalpiniaceae) in its natural habitat in Central Somalia

Cordeauxia edulis, the yeheb (yicib, ye-eb), has attracted much interest as a potential multi-purpose shrub well adapted to (semi)arid conditions. Since there exist only limited information and analyses, mainly of the seeds, we try to answer some questions arising about site conditions, soil requirements, and, by leaf analyses, the state of nutrition. Finally we determined the fodder-value of the foliage, as the bush is grazed too. Our results underline the low requirements of the yeheb for water and soil fertility.

Nutrient disorders and nutrient management in fast growing plantations

The negative impact of fast-growing tree plantations, especially when grown in short rotations, on nutrient reserves of poor tropical soils is often described. The intensity of soil and forest degradation may be assessed by different approaches, including detailed observation of deficiency symptoms and yield development, foliar and soil analyses, as well as diagnostic fertilizer experiments. Input/output analyses, taking into consideration water and nutrient fluxes between the different plant and soil compartments are means to evaluate the sustainability of tropical tree plantations. Only a small amount of data is available up to now, indicating poor sustainability. Soil and tree nutrient status can be improved by the application of mineral fertilizer, which is usually rapidly effective. In contrast, amelioration by management practices is only slowly effective, nevertheless important in view of sustainability, environmental protection and biodiversity. A big gap exists in reliable data on water and element dynamics in forest plantations with different tree species under different ecological conditions, and under different management practices.

Soils and reforestation in the central rangelands of Somalia

Abstract Representative soils of the Central Rangelands of Somalia were described between Bulo Burti and Galcayo. Limitations in land use are caused by aridity, salinity, shallowness, erosion, and alkalinity, as well as by the low nutrient status. Therefore, only less intensive reforestation is possible. Suitable methods are rainwater harvesting and irrigation with river water. Fuelwood and fodder species for community (fuelwood and fodder) and environmental reforestation are recommended. The protection of the natural regeneration is another important part of forestry and range management. Initially established plantations in the shebelli floodplain show that introduced species of Prosopis chilensis and Parkinsonia aculeata, as well as the native Acacia nilotica and Balanites aegyptiaca, are well adapted for reforestation in this area, whereas Azadirachta indica can be established only with difficulty and is not considered suitable.