Soil organic carbon loss and net nitrogen mineralization dynamics in unfertilized successive greenhouse tomato crops

Understanding and predicting soil organic carbon (SOC) dynamics and the soil’s capacity to supply nitrogen (N) to crops is challenging. Many soil properties, such as texture, moisture, temperature, pH, and soil management practices like tillage, influence SOC and organic N dynamics. This complexity justifies quantifying SOC and N mineralization in the field. This study aims to determine the SOC loss and net N mineralization in greenhouse tomato monoculture over five tomato growing seasons. The SOC loss per crop cycle was assessed as the difference between the SOC at the beginning of one crop cycle and the SOC at the beginning of the next. The SOC loss rate was compared with the loss in open-field systems simulated by a model validated in Uruguay. An N mass balance was conducted to determine N mineralization from SOC and net soil N mineralization. The total SOC loss during the three years was 11.3 Mg ha-1 (25.6 %), almost doubling the SOC loss in open-field predicted (6.6 Mg ha-1, 14.6 %). Annual mineralized soil N was higher in 2019, 594 kg ha-1, compared to 2021 (398.3 kg ha-1). We obtained annual N mineralization rates ranging from 4.6% to 8.0%, which varied with growing-season temperature. SOC loss and net N mineralization decreased across successive tomato crops due to depletion of soil C and N stocks, resulting in a significant reduction in tomato yield without fertilization. This knowledge will help improve soil management and organic amendments to prevent soil degradation and enhance soil N supply, thereby improving fertilization plans for greenhouse crops.