The assessment of soil respiration and nitrogen (N) mineralization under the addition of organic fertilizers is a matter of ever increasing interest. Aiming at a deeper insight into the subject, an aerobic liquid-based incubation was set up for the coupled respiration and N-mineralization over 360 h in a closed system, comparing one compost and one vinasse at rates of 300 and 600 mg N/kg soil, plus an unfertilized control. The system allowed the manometric measurement of themicrobial activity, and the N-mineralization in the suspension via solely NH4-N
determination. A set of substrate-induced respiration (SIR) tests was run to investigate the effects of nutrients and nutrients glucose addition on the soil respiration and N-mineralization of the five fertilizer treatments, in comparison with basal respiration in water. In water, compost showed a total net N-mineralization of +0.7 and -6.3% at the low (C1) and high (C2) dose respectively, whereas vinasse nominally reached 100% for both doses (V1 and V2). Soil respiration ranged between 3,269 and 18,389mg O2/kg dry soil of the unfertilized and V2. SIR tests showed that the respiration of compost-treated soil was boosted by nutrients in C2 more than in C1. Conversely, C1 was boosted by nutrients+glucose more than C2, indicating a combined of a nutrient- and carbon dose-dependent mechanism. These findings were confirmed by the N-mineralization, because C2 consumed almost threefold the NH4-N added to the system compared to C1. Vinasse-fertilized soil received a similar benefit from nutrients and nutrients+glucose. The additions of inducing substrates showed how compost and vinasse respiration are dose dependent: the lower the dose, the higher the respiration relative to the amount of added carbon in a carbon starved system. The incubation method adopted here appears to be a valid and rapid tool in the study of the effects of energy and nutrient constraints on respiration and N-mineralization dynamics in soils amended with biosolids
