Residual effects of papermill biosolids and forest-derived alkaline materials on crop yield and plant metal accumulation

Combined papermill biosolids (PB) and forest-derived alkaline by-products are known for their direct benefits to agricultural crops, but their residual effects after several years of application have received little attention. A 10 yr field study was initiated on a loamy soil at Yamachiche, QC, to assess the residual effects of PB application after nine consecutive years, either alone or with several liming by-products, on nitrogen (N), phosphorus (P), and metal accumulation in plant and crop yield. The treatments consisted of PB at 0, 30, 60, and 90 Mg wet·ha−1, three liming by-products (calcitic lime, lime mud, and wood ash), each at 3 Mg wet·ha−1 with 30 Mg wet PB·ha−1, and a mineral N fertilizer (MIN). During the residual years, only the MIN treatment was carried out every year according to crop needs. Grain yield and total plant N and P accumulation were evaluated each year, whereas metal accumulation was determined on a 3 yr cycle. The residual effects of PB applications increased crop yields in some years, but the effects were generally lower than with MIN. Plant N recovery in the first three residual years was half of that recorded during years of application (15% vs. 30%), whereas P recovery was at 6%. Residual PB applications had little effect on metal accumulation in grain. Soil liming decreased zinc and cadmium concentrations in grain but increased molybdenum. This study showed that repeated applications of PB and alkaline materials continued to have a positive effect on field crops 3–5 yr after their cessation.