Mineralization of azolla n and its availability to wetland rice: I. Nitrogen Mineralization of Different Azolla Species as Affected by Their Chemical Composition uri icon

abstract

  • The effect of Azolla species and their chemical composition on the mineralization of nitrogen in Azolla was studied. Phosphorus-enriched Azolla strains of Azolla pinnata var. imbricata #5, A. mexicana #2026, A. microphylla #4018, and A. pinnata var. pinnata #7001 were grown in a P-deficient wetland field. As Azolla grew, the P contents decreased. From 12 to 24 d after inoculation, the P deficiency became severe, the N contents decreased and the lignin and fiber contents increased. A. pinnata var. pinnata exhibited a lower N content than other species. Plants with different N contents were incubated for 4 weeks in the laboratory under flooded conditions to examine the process of N mineralization. Mineralization ratios (N mineralized/N added) were different between the two experiments. In one experiment, maximum mineralization at 4 weeks was 90%, and in another, 40%. As the N contents decreased, the mineralization ratios decreased. Correlation coefficients of the mineralization ratios after a 2-week incubation with N content were 0.51 in experiment 1 and 0.95 in experiment 2. In experiment 2, the mineralization ratios of N in Azolla plants with a N content lower than 3% were zero for a 4 week incubation, and in experiment 1, 40%. The lignin and fiber contents were negatively correlated with the mineralization ratios. The peaks of the quantity of mineralizable N were detected at 12 days after inoculation, when Azolla started to be P-deficient. These results indicate that Azolla plants deficient in P and low in N show low mineralization ratios, and probably a low fertilizer efficiency.

publication date

  • 1991
  • 1991
  • 1991