Chemical properties of two soils irrigated with thermo-mechanical pulp mill effluent

The effect of land application of thermo-mechanical pulp (TMP) mill effluent on soil chemical properties was examined using barrel lysimeters. Twelve lysimeters, 500 mm in diameter and 800 mm high, containing either a volcanic soil (Udivitrand) or a pallic soil (Haplustalfs), were collected from 2 plantation forest sites. A TMP mill effluent containing high concentrations of total organic C (1136 mg/L) was irrigated at 30 mm/week over a period of 16 months. Soil sample analysis indicated that build up of soil organic C was negligible despite large additions of organic C (equivalent to 19 t/ha) through irrigation with TMP mill effluent. Mass balance calculation implied that microbial degradation or mineralisation of the organic compounds might be the main mechanism involved in the high renovation rates. Irrigation with TMP mill effluent significantly increased soil pH, concentrations of soil total S, available P, and exchangeable K and Na, but it had no significant effect on concentrations of soil total N, and exchangeable Ca and Mg. The results from this study indicate that TMP mill effluent irrigated at a loading rate not greater than 30 mm/week would cause little detrimental effect on the quality of soils at these 2 plantation forest sites.