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Asian Journal of Plant Sciences

Year: 2005 | Volume: 4 | Issue: 4 | Page No.: 392-400
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Authors

F. Azam

M.H. Sajjad

A. Lodhi

R.M. Qureshi

Keywords

Research Article

Changes in Forms of N During Decomposition of Leguminous/Non-leguminous Plant Residues in Soil and Fate of 15N-labelled Fertilizer Applied to Wheat (Triticum aestivum L.)

F. Azam, M.H. Sajjad, A. Lodhi and R.M. Qureshi
Experiments were conducted under greenhouse conditions to study I) the dynamics over time of mineral N, mineralizable N and humus N during decomposition in soil of leguminous and non-leguminous plant material and ii) the impact of these changes on growth and N nutrition of wheat fertilized with 15N-labelled ammonium sulphate. Finely ground straw of wheat, maize and sesbania was allowed to decompose in soil for 0, 2, 4 and 8 weeks. Sub-samples of soil were analyzed for the content of mineral N, mineralizable N and humus N. The bulk soil was sown to wheat and the plants harvested at maturity. Nitrogen as 15N-labelled ammonium sulphate was applied in two split doses of 40 and 60 mg kg-1 soil. Accumulation of mineral N in soil during 8 weeks of residue decomposition was found to depend on the chemistry of plant residues, more mineral N being released in soil amended with plant residues with narrow C/N ratio i.e., maize and sesbania. These residues also contributed more to humus N and maintained a higher content of potentially mineralizable N. Wheat straw not only caused a net immobilization of N during 8 weeks of aerobic incubation but a substantially higher loss of NO3¯+NO2¯ -N during subsequent incubation under submerged conditions. The loss of NO3¯+NO2¯ -N was more where residues were given less time for decomposition. Plant residues applied immediately before sowing wheat or those allowed shorter period of decomposition had a negative effect on plant growth. Of the three residue types, wheat straw caused a higher reduction in plant growth. This was attributed mainly to significantly reduced availability to plants of soil-N, while uptake of fertilizer N was affected almost similarly by the three types of residues. Residues of maize and sesbania had a positive effect on grain yield and total biomass of wheat. As a whole, ca 30% of the fertilizer N applied was taken up by the plants and >40% was unaccounted in the soil-plant system, fertilizer N remaining in soil being <30% of the applied. Relatively higher proportion of the applied N remained in amended than unamended soil after crop harvest.
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