The response of roots of Mucuna pruriens var. utilis to aluminium depends on the duration of exposure and the type of experiment. In a short-term study, the usual reduction of root elongation rate by Al was found. In contrast, a study for a longer period of time, 4 weeks, showed a stimulation of root dry weight and root surface area for 110 or 185 M Al3+, compared to a no-Al control. In a split-root experiment, the response of root growth to the presence of Al3+ in its environment depended on the presence or absence of Al3+ around other parts of the same root system. It was concluded that Al avoidance, rather than Al toxicity or tolerance, explained the root response of Mucuna to acid subsoil conditions in the field. The question was addressed as to whether the Al-avoidance reaction is related to a local response of plants to P stress, leading to increased branch root development close to a P source. Increasing the P supply to the roots indeed resulted in the disappearance of the Al-avoidance reaction in Mucuna. An experiment with the more Al-tolerant Centrosema pubescens demonstrated that Al avoidance is not restricted to Mucuna species. The Al avoidance described here has an important bearing on selection of crop cultivars for a better root development in acid subsoils. To obtain cultivars with a deep root development in acid subsoils, it is not sufficient to screen for Al tolerance of single roots or intact root systems in a homogeneous medium; it is necessary to test for Al avoidance in heterogeneous media.
Tag: aluminium
Screenhouse performance of VAM-inoculated seedlings of Leucaena leucocephala (Lam.) De wit. in a phosphorus-deficient and aluminum sulfate-treated medium
The effect of 3 species of vesicular-arbuscular mycorrhizal (VAM) fungi on the growth of Leucaena leucocephala (Lam.) De Wit. in a phosphorus-deficient and aluminumsulfate (AIS)-treated medium was investigated in a screenhouse experiment. Plant height, root length, nodulation, phosphorus uptake and nitrogen fixation were used as indices of plant performance. While there were significant differences among mycorrhizal plants with respect to these indices, they outperformed their non-mycorrhizal counterparts in all respects except in nitrogen content. Of the 3 mycorrhizal species studied, Glomus etunicatum (Becker and Gerd) was the most efficient, followed by Glomus fasciculatum (Thaxter) Gerd and Trappe, and finally, Gigaspora margarita (Becker and Hall). Both aluminumsulfate and mycorrhizal treatments increased shoot dry weight.
Plant nutritional problems in marginal soils of developing countries
This chapter presents the global distribution of the major problem soils of the world, with special emphasis on soil chemical constraints on agricultural production. The focus is on developing countries particularly in sub-Saharan Africa where food security is endangered by soil constraints. The most widespread constraints, aluminium toxicity and phosphorus deficiency are highlighted. It is argued that the major cause of the decline in food production in Africa is not inherent infertility, but rather soil fertility depletion resulting from years of continuous cropping with few external inputs. Various options for agricultural development of problem soils are presented; highlighting the use of organic inputs. Finally approaches currently under study at ICRAF, in which new techniques suitable for assessment of soil fertility status are detailed.