Microbial biomass and bacteria in two pasture soils: An assessment of measurement procedures, temporal variations, and the influence of P fertility status

Abstract

The reliability of three methods (microbial C and mineral-N flush by fumigation-incubation, and ATP) for measuring soil microbial biomass was assessed on two silt-loam soils of different P fertility status under grazed perennial pastures. The mineral-N flush and ATP methods provided a reasonably reliable index of microbial biomass, but the fumigation-incubation procedure for CO2-C flush, using preincubated samples and an unfumigated 0-10 day control, was inappropriate for these soils. The numbers of bacteria (direct microscopy) and the percentage metabolically active were also measured.Generally, in both soils, total microbial biomass and the numbers, mass and metabolic activity of bacteria were influenced more by temporal factors in samples taken monthly than by the fertility status. Temporal fluctuations were greater in the high-fertility (Waikanae) soil, but no consistent seasonal trends in mineral-N flush and ATP values were apparent. In both soils, numbers and biomass of bacteria were at a minimum in spring.Values of two biomass indices (mineral-N flush and ATP contents) were similar in the high-and low-fertility (Pomare) soil, and comprised similar percentages of organic-matter contents. The percentages of metabolically active bacteria, however, tended to be higher in Pomare than in Waikanae soil, and, therefore, did not reflect soil fertility status.Methodological and field aspects of these results are discussed.

Influence of pasture management on soil biological quality

“…Tate et al (1991) advocated the use of fresh rather than pre-incubated soil, favoring the more versatile extraction procedure for measuring soil microbial biomass, especially for pasture soils. Banerjee and Chapman (1996) icantly (P<0.001) during the year, lowest in samples taken in summer, the driest time of the year, and higher in spring (Table 6).…”

Influence of urea fertilization and urease inhibitor on the size and activity of the soil microbial biomass under conventional and zero tillage at two sites

“…1990) and 0.45 (Jenkinson 1988) respectively. Biomass determinations were made on field-moist soil (Tate et al 1991 …”

Resíduos orgânicos como recondicionante de subsolo degradado e efeitos na atividade microbiana e fertilidade em cultivo de barbatimão

“…(CBM), efeito também conhecido como influência sazonal, em virtude da elevação da temperatura e da pluviosidade (TATE et al, 1991), que atinge principalmente as camadas superficiais do solo, onde as oscilações de umidade e temperatura são maiores (CATTELAN e VIDOR, 1990 Os valores de C-CO 2 liberado foram superiores em 52% nas áreas com resíduos vegetais, em comparação com as áreas sem os citados resíduos, resultados semelhantes aos relatados por Assis Júnior et al (2003).…”