Dynamics in microbial immobilization and transformations of phosphorus in highly weathered subtropical soil following organic amendments

To improve knowledge on the role of microbial processes in phosphorus (P) transformations in highly weathered subtropical soil, dynamics in microbial biomass C (BC) and P (BP), and Olsen-P in a subtropical Ultisol following amendments with glucose at 2 g C kg−1 soil (G2) and rice straw at 2 and 4 g C kg−1 soil (RS2 and RS4) was studied during a 43-day incubation period at 25°C and 45% of soil water-holding capacity. By 3 days, the amount of soil BC had increased about 3.2, 1.7, and 2.6 times for G2, RS2, and RS4, respectively. The amount of soil BC significantly decreased between 3 and 7 days for G2 and 3 and 14 days for RS4, and thereafter remained almost steady throughout the 43-day incubation period, at levels about 1.6–2.4 times larger than for the control (no organic amendment; CK). The amount of soil BP for G2 and RS4 almost doubled by 3 or 7 days, then remained relatively steady, and for RS2, maintained relatively constant (6.7–8.2 mg kg−1 soil) throughout 43-day incubation period, whereas it declined by about 50% for CK. A significant decrease (3.5 mg kg−1 soil) in Olsen-P occurred in G2 by 3 days; indicating a close response of available P to microbial immobilization. Also, the amounts of Al- and Fe-bound P in G2 and Fe-bound-P in RS4 decreased significantly, as determined at 43 days. In conclusion, organic amendment enhances microbial immobilization and transformations of P, but the turnover of BP behaves in different patterns as BC in highly weathered subtropical soil.