Environmental impact of repeated applications of combined paper mill biosolids in silage corn production

Abstract

Paper mill biosolids (PB) may provide benefits for crop yields and soil nutrients. However, few data are available on metal accumulation and pathogenic populations resulting from applications in silage corn production. A study was initiated to determine the effect of annual spring application of combined PB during 3 consecutive years, with or without calcitic lime, on yield and on the environmental risk posed by N, P, heavy metals (Cu, Zn, Cd, Mo) and Escherichia coli to a silage corn cropped in a loamy sand in eastern Ontario, Canada. Treatments consisted of complete mineral NPK fertilization (PB0), 30 Mg wet weight ha-1 with supplemental N and K, and 60 and 120 Mg wet ha-1 supplemented with K, either with or without 2.5 Mg ha-1 calcitic lime. The PB at 30 Mg wet ha-1 with reduced mineral N and PB at 60 Mg wet ha-1 provided comparable yields to the mineral N fertilization in all years, whereas application of PB at 120 Mg wet ha-1 increased corn yield by 6.0 Mg ha-1 in the third year. After 3 yr, contents of soil NO3-N and the P saturation index (P/Al) were increased, indicating a possible risk of nitrate and P leaching. Lime increased soil pH by 0.8 unit, which in turn caused a large increase in the tissue Mo concentration and Mo uptake by silage corn. The PB, particularly at 120 Mg wet ha-1, produced significant accumulations of Cd and Zn in soil, plant tissue and uptake. The PB showed small counts of E. coli, and consequently very little contamination was observed in the soil and on the harvested crop. Based on these results, the PB used are a good source of nutrients that benefits silage corn yields and represent as well a low risk for human and animal health and for the environment when the application does not exceed 60 Mg wet ha-1 yr-1.Key words: Zea mays L., paper mill biosolids, lime, heavy metals, cadmium, molybdenum, Escherichia coli