Abstract
The effects of incubation time, vegetation type (represented by a pine plantation, a protected and a periodically burnt eucalypt forest), lime and finely ground pine needles on the transformation of ( 15NH 4) 2SO 4 and K 15NO 3 were studied in incubation experiments with a sandy lateritic podzolic soil from south-east Queensland. Microorganisms were counted so as to relate N transformations to particular groups of microorganisms. The heterotrophic miroflora utilized NH + 4 as a source of N in preference to NO − 3, and autotrophic nitrifiers seemed to be weak competitors for NH + 4. Lime caused a slight loss of NO − 3 and this was accompanied by an increase in the population of denitrifying bacteria. Lime promoted immobilization of NH + 4 by heterotrophic bacteria and subsequent mineralization by nitrifying bacteria, but when pine needles were also added the nitrifiers were suppressed and immobilization by heterotrophic bacteria dominated. Pine needles alone stimulated fungi to immobilize NH + 4. While reforestation with exotic pines caused a loss of total-N there was evidence of increased turnover, i.e. more rapid immobilization and nitrification, in pine plantation soils. Prescribed burning also promoted nitrification while reducing total-N.
Published Version
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