Influence of one or two successive annual applications of organic fertilisers on the enzyme activity of a soil under barley cultivation

The effect of cow manure and two rates of addition of municipal solid waste (MSW) compost on the enzymatic activity of a soil supporting barley cultiv ation was studied and compared with mineral fertilisation (MF). The experim ent was carried out in unirrigated land in field conditions for two years. One set of plots was fertilised only once, at the start of the experiment, while another set of plots was fertilised annually (before each sowing). In general, the organic amendments stimulated soil enzyme activity but mine ral fertilisation did not. The annual addition of large quantities of MSW c ompost, in general, led to lower levels of enzyme activity than similar rat es of amendment in the plots receiving a single addition, probably because of the toxic effect which the heavy metals incorporated with the MSW compos t had on microbial development. In the second year, plot receiving a single application of organic amendment showed higher protease hydrolysing casein , beta -glucosidase and dehydrogenase activities than control or soil with mineral fertilisation. This implied that the addition of organic waste, and particularly MSW compost. had a catalysing effect in the soil which lasted for the following years. Barley yields obtained with organic amendments we re, in general, similar to, or even higher, than those obtained with minera l fertilisation. The annual addition of high doses of compost had an inhibi tory effect on enzyme activity and barley yield (compared with the results obtained with the low addition of compost) due to the negative effect of th e heavy metals incorporated with the compost. (C) 2001 Elsevier Science Ltd . All rights reserved.