EFFECTS OF SOIL-MANAGEMENT HISTORY ON THE RATE OF ORGANIC-MATTER DECOMPOSITION

In a sustainable agriculture farming systems experiment; soils managed under organic farming practices had greater microbial abundance and a ctivity, and higher numbers of bacterial-feeding nematodes during crop growth, than those managed under conventional farming practices. We t ested rates of organic matter decomposition in the two soils and monit ored the abundance and activity of soil biota during the decomposition process. Differences in soil biology between soils from organic and c onventional farming systems did not persist when soils were amended wi th organic matter and maintained under similar conditions. Microbial c ommunities in soil from the conventional system were sufficient and ac tive enough to respond to organic inputs. There were minimal differenc es in the ability of the microbial communities of the two soils to dec ompose organic residues. However, when soils were removed from the hel d at different times, cover crop decomposition rates were more consist ent in the organic soils, suggesting a greater abundance and diversity of the microbial community in those soils. Microbial activity was mos t suppressed when held soils were dry but responded to organic matter amendment very rapidly when favorable moisture contents were restored. The pattern of microbial activity in both organic and conventional so ils following organic matter incorporation consisted of a 100 h activi ty phase and then a gradual decline to a relatively constant stasis ph ase. (C) 1998 Elsevier Science Ltd. All rights reserved.