Jgm. Guerra et al., PHOSPHORUS-CONTENT IN THE SOIL MICROBIAL BIOMASS UNDER BRACHIARIA-DECUMBENS STAPF, Pesquisa agropecuaria brasileira, 30(4), 1995, pp. 543-551
Following a long-term experiment on the growth of Brachiaria decumbens
fertilized with different sources of phosphorus applied at different
times, a study was performed to estimate the phosphorus in the microbi
al biomass using the fumigation-extraction method. The treatments were
: no P fertilization (PO), rock phosphate incorporated 60 days before
planting (RFpl), rock phosphate 60 days before planting and triple sup
erphosphate applied 3 years later (RFpl + STcob), superphosphate at pl
anting (STpl), superphosphate at full leaf cover (STcob), and superpho
sphate at planting and 3 years later (STpl + STcob). The addition rate
at each of the two stages of fertilizer application was equivalent to
87 kg P/ha. The microbial P increased from 7.7 to 13.7 mg P/kg soil w
hen the soil was fertilized with superphosphate, either at planting, o
r three years later at full leaf cover, resulting in an increase in th
e P concentration in the biomass from 10.6 to 21.2 g P/kg biomass in t
he same treatments. There was a tendency for the application of superp
hosphate to cause a decrease in the C:P ratio of the biomass independe
nt of the date of application. Thus, the plots fertilized with superph
osphate at planting and again 3 years later, did not result in any inc
rease in the P content in the microbial biomass when compared with the
plots fertilized only at planting, showing that even after 5 years of
growth of Brachiaria the soil microbial biomass was found to be highe
r in P than in the treatment where there was no P fertilization. The m
icrobial P was shown to be a promising parameter for studies of the fa
te and dynamics of P in the soil.