Tropentag, October 5 - 7, 2004 in Berlin "Rural Poverty Reduction through Research for Development and Transformation"

Indication of Phosphorus Nutrition in a Calcareous Soil in Bangladesh

Georg-August-Universität Göttingen, Institute of Agronomy and Animal Production in the Tropics and Subtropics, Germany

Abstract

In a calcareous soil, phosphorus (P) nutrition appears to be a limiting factor for successful crop production. To make use of a strategic P nutrition to grow maize in Bangladesh soil (initial carbon 2.2%), a mixture of organic and inorganic P sources (23 kg/ha P) as F0, F25 and F50 (100% inorganic + 0% organic, 75% inorganic +25% organic and 50% inorganic +50% organic P, respectively from oil cake, bone meal and triple super phosphate) were used. In addition biological agents Glomus manihot (Gm) a (V) AM mycorrhizal fungus, Bacillus megaterium var. phosphaticum (Bm) a phosphorus-solubilising bacteria and Rhizobium leguminosarum (Rh) a nitrogen fixing bacteria were applied in a factorial design. A modified sequential phosphorus fractionation scheme by Tiessen and Moir (1993) was followed to determine the labile (0.5 M NaHCO₃ extractable), Al and Fe associated P (0.1 M NaOH extractable), Ca associated P(1 M HCl extractable) and residual P (Conc. H₂SO₄ and H₂O₂ digestible). pH of the initial soil was 7.6, which remained unaffected by the treatments. Available P (Olsen P) was found to increase from initial 6.0 upto 13.4 mg/kg soil after the treatment. All the treatments showed an increase in available P with the increase in organic sources except Rh, which showed a reverse trend. Sequential fractionation of phosphorus showed a large quantity of Ca-associated (HCl extractable P) phosphorus between 450 to 485 mg/kg out of 793 to 865 mg/kg of total P. Among the treatments Rh was found to cause a decrease in NaOH and HCl extractable inorganic P with increased organic P source. Labile inorganic P (Pip) and organic P (Porg) were varying most within the treatments. It ranged between 24.5 to 30.2 mg, 22.0 to 34.7 mg 2.7 to 12.9 mg and 0.8 to 10.9 mg per kg soil in NaHCO₃-Pip, NaOH- Pip, NaHCO₃-Porg and NaOH-Porg, respectively. Glomus manihot and Bacillus megaterium var. phosphaticum were able to enrich organic and inorganic P pools in comparison to Rhizobium. Organic sources of P fertiliser appeared to improve P availability to the crop and biological agents contributed to drive P among the organic and inorganic pools.

Keywords: Organic P source, P availability, P nutrition, phosphorus fractionation

Contact Address: Saiful Md. Islam, Georg-August-Universität Göttingen, Institute of Agronomy and Animal Production in the Tropics and Subtropics, Grisebachstrasse 6, 37077 Göttingen, Germany, e-mail: saifpabhotmail.com