Papermill Lime‐Sludge as an Alternative Liming Material 1

Calcitic papermill lime‐sludge, a by‐product of the kraft paper process, was evaluated as a liming material and its equivalency with dolomitic agricultural limestone determined. An incubation study involving 10 medium‐ or light‐textured Wisconsin soils demonstrated that lime‐sludge neutralizes soil acidity very rapidly. Maximum soil pH was achieved in less than 1 week after application of the lime‐sludge, while the pH of soils treated with finely‐ground agricultural limestone increased continuously throughout the 24‐week incubation period. In field trials conducted for 3 years on two different soils, corn ( Zea mays L.) was followed by alfalfa ( Medicago sativa L.) or birdsfoot trefoil ( Lotus corniculatus L.). Both legumes responded favorably to liming but not differently to the lime‐sludge and agricultural limestone, whereas a response was not observed for corn. Yield data provided no evidence that use of the calcitic lime‐sludge created Mg stress in any tested crop. Plant tissue analyses and the absence of a yield response to soil‐applied MgSO 4 •7H 2 O supported this observation. The liming equivalency of lime‐sludge to agricultural limestone was examined under both laboratory and field conditions. Both suggested that 1 m 3 of the lime‐sludge has the same liming value as 1.1 metric tons of agricultural limestone with a neutralizing index of 60 to 69. This value is considerably less than the equivalency of 1.5 yd. 3 of lime‐sludge per ton of 60 to 69 agricultural limestone specified by Wisconsin Administrative Code.