Saturday, 15 July 2006

Soil Microbial Biomass and Activity under Different Soil Management in a Brazilian Oxisol.

Elcio L. Balota, Agronomic Institute of Paraná (IAPAR), Soil Science Dept, Caixa Postal 481, 86001-970, Londrina, Brazil and Richard P. Dick, The Ohio State Univ, School of Nature Resources, 2021 Coffey Road, Columbus, OH 43210-1085.

There is increasing pressure to produce greater amounts of food and fiber due to the continual rise of the world's population. In many regions of the world, including Brazil, forest areas are being converted to intensive agricultural management. To have sustained productivity of these soils and to understand the long-term impacts of this conversion, information is needed on how this affects microbial properties of soils. The objective of this study was to compare forest soil with soils that had been converted 22 yrs ago to coffee production or to Conventional (CT) and No-Tillage (NT) crop systems relative to microbial biomass and activity. The study was done on an Oxisol (Typic Haplorthox) at the IAPAR Experimental Station in Londrina, Brazil. Soil samples were taken at 0-5, 5-10 and 10-20 cm depths in October 1997 and March 1998 and evaluated for microbial biomass C and N, mineralizable C and N, and aggregate stability. Soil management influenced significantly all parameters at all depths. The cultivated sites had lower microbial biomass and activity than forest site. Microbial biomass C and N was respectively, 1068 and 279 kg ha-1 for forest, 336 and 123 kg ha-1 for coffee, 225 and 84 kg ha-1 for CT, and 542 and 99 kg ha-1 for NT. Although the forest and NT sites had higher microbial biomass and activity than CT site the metabolic quotient was 65% and 43% lower, respectively. After 22 years of cultivation the total C declined 22% under coffee, 43% under CT, and 32% under NT, while the decline of microbial biomass C was 69% for coffee, 79% for CT, and 49% for NT. These results suggest that the microbial biomass represents a substantial reserve of N in the study sites and may contribute substantially to the N requirements of crops.

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