Effect of applying paper mill sludge to arable land on soil fertility and crop yields

Two field trials were established in 1991 to determine the effects on crop yield, N uptake, soil moisture content and heavy metal concentration of app lying de-inked paper mill sludge (DPMS) over the period 1991 to 1993. In th e first ear, during decomposition of the DPMS, N immobilization occurred re sulting in loss of cereal yield (P < 0.05) at low rates of N fertilizer. Ap proximately 40 kg extra N fertilizer/ha was required per 100 t DPMS/ha to c ompensate for this N immobilization. Soil volumetric moisture content was i ncreased (P < 0.001) by c. 20% at both sites by 200 and 300 t DPMS/ha. DPMS did not significantly increase (P > 0.05) soil concentrations of total Zn, Cu and Pb. Soil nitrate concentrations after harvest were reduced (P < 0.0 1) by c. 17 mg N/kg per 100 t DPMS/ha with increasing rates of DPMS up to 2 00 t/ha. In the second year following the DPMS application, there were no s ignificant effects on grain field indicating that very little or no N was i mmobilized. By the third year, the soil N supply was 7 kg N/ha higher where a single dressing of 100 t DPMS/ha had been applied compared to the contro l. This resulted in an overall yield increase of 7% (P < 0.10). Soil N supp ly was lower (N.S.) but crop yields were similar (P > 0.05) to the control where single dressings of 200 and 300 t DPMS/ha had been applied.