Beneficial use of paper-mill residue compost in a potato/spring wheat rotation

Paper sludge compost may improve the nutrient status and biochemical proper ties of coarse-textured soils devoted to intensive potato production. A stu dy was conducted in 1997 and 1998 to assess the impact of the addition of a compost of primary papermill sludge and liquid hog manure, used alone or i n combination with inorganic fertilizers, on soil nutrient status, fluoresc ein-diacetate activity (FDA) and C-CO2 evolution and on the yields of potat o (Solanum tuberosum L. cv. Hilite Russet) and wheat (Triticum aestivum L. cv. AC Barrie) grown in a Bevin loamy sand (Orthic Humo-Ferric Podzol) loca ted in St-Ubalde, Quebec, Canada. Compost was applied in the spring of 1997 at 0, 40, 80 and 120 Mg ha(-1) on a wet basis, and supplemented or not wit h 0 to 225 kg ha(-1) of N, 0 to 300 kg ha(-1) of P2O5 and 0 to 200 kg ha(-1 ) of K2O. The compost was incorporated in the top 10 cm of soil. Inorganic fertilizers were fractionated at planting and hilling. No fertilizer was ap plied in the second year. Compost significantly influenced the KCl-extracta ble soil N content at 45 days after planting and the Mehlich-3 extractable P at potato harvest. These effects lasted only one year for N. Compost addi tion at 40 Mg ha(-1) resulted in the highest FDA and C-CO2 evolution. The a ddition of 40 Mg ha(-1) of compost produced the best marketable potato tube r yields independently of fertilizer supplement. This 40 Mg ha(-1) of compo st, along with 75 to 150 kg ha(-1) of N or 100 to 200 kg ha(-1) of P2O5 pro duced the highest tuber yields. In 1998, the best wheat grain yield was obt ained with compost at 80 Mg ha(-1). The addition of compost at 120 Mg ha(-1 ) was excessive. Compost, when added at 40-80 Mg ha(-1), increased the inor ganic fertilizer efficiency by improving crop yields and soil biochemical s tatus.