Soil carbon and nitrogen mineralization kinetics in organic and conventional three-year cropping systems

The scientific literature regarding the use of C and N mineralization kinetics as a tool to highlight the effects of different cropping systems on soil C and N release is scarce. In this study we aimed to assess the effectiveness of these parameters in evaluating soil C and N potential release in organic (ORG) and conventional (CONV) three-year cropping systems. A long-term field study was established in 2001 at the University of Tuscia experimental farm (Viterbo, Italy) in a randomized block design. The soil is classified as Typic Xerofluvent or Dystric Fluvisol. In the CONV system the Good Agricultural Practice is adopted, whereas the ORG system is managed following the Regulation 2092/91/EEC. Both systems had a three-year crop rotation (pea – Pisum sativum L.; durum wheat – Triticum durum Desf.; tomato – Licopersicum esculentum Mill.). One of the main differences between the two systems is the soil N fertilization program: organic fertilizers (Guano: 6% N, 32% organic carbon and DIX10: 10% N, 42% organic carbon, both produced by Italpollina, Italy) and mineral nitrogen fertilizers (NH4NO3) were applied to ORG and CONV fields, respectively. Moreover, the rotation in the ORG system included common vetch (Vicia sativa L.) and sorghum (Sorghum vulgare L.) as green manure crops. Our results supported the hypotheses in that the two systems differed significantly on potentially mineralizable C (C0) in 2008 and on potentially mineralizable N (N0) as nitrate form (N0-NO3−) in 2006 (318 μg C-CO2 g−1 28 d−1 vs. 220 μg C-CO2 g−1 28 d−1; 200 μg N-NO3− g−1 vs. 149 μg N-NO3− g−1 in ORG and CONV, respectively). The reduction of N0 in soil during the crop rotation period could reflect the N microbial immobilization since a negative correlation between microbial biomass N:total N ratio and N0 as ammonium form (N0-NH4+) (P < 0.001) as well as a positive correlation between N0-NH4+ and C:N ratio of microbial biomass (P < 0.05) were observed. Moreover, a lower potential mineralization rate of N was observed in soil with Guano (25%) than in soil with DIX10 (35%); nevertheless the former fertilizer might cover a longer period of crop N demand as a more gradual release of N0 was observed. In this work we demonstrated that the use of mineralization kinetics parameters can offer a potential to assess the mineralization–immobilization processes in soils under different climatic and management conditions. Moreover, they can be used to evaluate the most suitable N release pattern of organic fertilizers used in various cropping systems.

Research highlights▶ The use of carbon and nitrogen mineralization kinetics parameters can offer a potential to assess the mineralization-immobilization processes in soils under different climatic and management conditions. ▶ The mineralization kinetics parameters can be used to evaluate the most suitable N release pattern of organic fertilizers used in various cropping systems. ▶ The Guano fertilizer might cover a longer period of crop N demand showing a more gradual release of potentially mineralizable nitrogen than DIX10.