Monitoring Microbiological Soil Parameters in Sugarcane Cropped Soils in Brazil.

Sugarcane is an important energy crop in Brazil. Since soil microbial biomass serves as plant nutrient pool due to its high lability, monitoring microbiological soil parameters seems reasonable to identify changes promoted by soil management. This study aimed to evaluate microbiological parameters in sugarcane cropped soils receiving different N fertilizer managements. Soil sampling was performed in eight N-response sugarcane trials in São Paulo State, Brazil, at 0-20 and 20-40 cm soil layer. Microbial biomass C (MB-C, µg MB-C g soil^-1) was measured in fresh soil samples, after incubation for 10 days (25 °C) by the chloroform fumigation-extraction method (CFE). The MB-C content was obtained by the difference between fumigated and non-fumigated samples. The basal respiration (BR, µg CO₂-C g soil^-1 h^-1) was estimated in non-fumigated soil samples during the incubation period. The same sample was used to estimate the induced basal respiration (BR-i, µg CO₂-C g soil^-1 h^-1), by glucose addition and further incubation for additional 3 days. The metabolic quotient (qCO₂, µg CO₂-C µg MB-C^-1 h^-1) was obtained from the relation between BR per unit of MB-C, while the qCO₂-i was estimated by the relation between BR-i and MB-C. The soil differed greatly in relation to MB-C content, with higher values for the sites 2, 3 and 6. The BR showed differences among soils and depths, with higher values for sites 2, 6 and 7, as well as for the 0-20 cm soil layer. The same pattern was verified for the BR-i. On average, BR enhanced by 32 and 39 times with glucose addition in the 0-20 and 20-40 cm soil layer, respectively. Sites 1 and 8 showed higher qCO₂ and qCO₂-i values possible due to the low organic C content (site 1) and the recent soil tillage practices (site 8). The BR and BR-i were positively correlated with MB-C at 0-20, 20-40 and 0-40 cm soil layers. Further measurements will be performed to evaluate sugarcane response to N fertilization, in order to identify the relationship between fertilizer response and microbiological soil parameters.