Nitrogen value of papermill biosolids used as fertilizer on temperate agricultural soils: a meta-analysis
Secondary and combined papermill biosolids (PB) are a well-known source of nitrogen (N) for crops, but the available information relating efficient N release to potential factors is fragmented. A meta-analysis was carried out, involving 26 independent studies and 121 observations from multiple experiments (92 for PB and 29 for fertilizer N as a reference). Varying factors related to crop practices, soil properties, and PB characteristics were investigated for their effects on crop yield and plant N accumulation in temperate agricultural regions. The results of meta-analysis revealed that the carbon-to-nitrogen (C/N) ratio of PB and material organic C added accounted for the differences in effect sizes for crop yields, particularly in field studies involving crops with a high N requirement. Conversely, effect sizes for plant N accumulation increased with high application PB rates and amount of total N applied. Moreover, both a low C/N (<15) and a high C/N (>25) ratio were found to increase effect sizes for plant N accumulation. No significant effect was detected for soil properties. Globally, 17% of the total N in PB, equivalent to 39% of fertilizer N, was recovered in the crop. The N recovery percentage was higher in crops with high N requirements and a long growing season, indicating that these crops benefitted more from the N released from PB and would be ideal recipients for PB application. Our results confirm the value of PB as N fertilizer and can help producers and agronomists to finetune their fertilization programs.