Using paper de-inking sludge to maintain soil structural form: Field measurements

A high level of organic matter in soils is crucial to maintain structural stability but organic matter sources differ in their effectiveness in stabilizing structural units. Objectives of this study were, first, to determine the optimal rate of sludge and fertilizer application to improve soil physical properties, and second, to investigate a possible correlation between hydraulic conductivity and structural stability measurements. A 4-yr field study (1994-1997) was conducted on three different soil types to evaluate the effect of different amounts of de-inking secondary paper sludge on the soil physical properties. The soil physical properties we monitored were structural stability, water desorption characteristics, bulk density, and saturated hydraulic conductivity. Structural stability was increased by 17% in silty clay soil (SCS) and 15% in loamy soil (LS), but decreased by 35% in sandy loam soil (SLS). Results suggest that the effect of sludge application (SA) is short-lived and that an annual application of sludge is necessary to obtain a year-to-year effect on structural stability. Measured bulk density dropped significantly in the SCS (4-10%) and in the LS (1-6%). A significant increase in air capacity and available water values revealed that SA increases both transmission and storage pores in the SCS. Field-saturated hydraulic conductivity (K(fs)) was increased in the SCS, but decreased in the SLS and the LS. A good correlation was observed between structural stability and hydraulic conductivity measurements in the SCS and the LS.