Soil Respiration and Nitrogen Mineralization Kinetics of Compost and Vinasse Fertilized Soil in an Aerobic Liquid-Based Incubation

Abstract

Abstract

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⁻¹ soil, plus an unfertilized control. The system allowed the manometric measurement of the microbial activity, and the N-mineralization in the suspension via solely NH⁺₄-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, the 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 18,389 mg O₂ kg⁻¹ 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 nutrient- and carbon dose-dependent mechanism. These findings were confirmed by the N-mineralization, because C₂ consumed almost threefold the NH⁺₄-N added to the system compared to C₁. Vinasse-fertilized soil received a similar benefit from nutrients and nutrients + glucose. Addition 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.