Irradiated digested sewage sludge: Effects on plant-symbiont associations in the field

Abstract

Anaerobically digested sewage sludge was irradiated with high energy electrons as a means of disinfestation at Boston's Deer Island Treatment Facility and transported to the Suburban Experiment Station of the University of Massachusetts, at Waltham. In May 1977, it was applied to limed field plots as liquid surface applications. Three plots were given a single application at the rate of 4·7 metric tonnes/ha dried sludge. Three other plots received double this amount (9·4 metric tonnes/ha). Three additional plots served as controls and received 111 kg/ha each of 10-10-10 N, P, K inorganic fertiliser. These applications were repeated with the same plots in May 1978. In both 1977 and 1978 sludge applications at both rates inhibited rhizobial nodulation of bush bean Phaseolus vulgaris L. ‘Contender’ and VA mycorrhizal infection in onion Allium cepa L. ‘Downing Yellow Globe’. Heavy metal accumulation in soil and plant tissue, pH, soluble salt levels and N and P status of sludge and soil were monitored throughout the experiment as possible explanations for these inhibitions. No readily discernible explanation was found.