Conventional and organic cropping systems at Suitia III: Microbial activity in soils

Helvi Heinonen-Tanski

doi:10.23986/afsci.72906

Abstract

From 1983 to 1988 the microbial activity of soil was measured by determining its nitrification potential, dehydrogenase activity, cellulolytic activity and respiration. The samples were Suitia silty clay soils under various types of conventional and organic cropping systems. The soil microbial activity was the highest in both organic cattle farm plots in the ley phase and conventional cattle farm plots in the ley phase. The difference between these two ley soils was not clear, partly because of the considerable statistical variance, but the microbial activity of organic cattle farm plots in clover leys tended to be higher than in conventionally cultivated grass leys. This favourable effect on dehydrogenase activity was not detected after poor overwintering in organic cattle farm plots in annual clover in 1984 and Persian clover in 1985, but some effect on nitrification was found in 1984. In many cases, soil microbial activity was still increased two to three years after the leys. The soil nitrification activities were often higher in organic plant production plots than in conventional plant production plots, but the dehydrogenase activities and cellulose decompositions of organic plant production plots were similar to those in conventional diverse plant production or barley monoculture plots.

Highlights

As Fitz Patrick (1986) stated, soils can be considered our major natural resource, because most of our food and clothing are derived from them directly or indirectly
Microorganisms are responsible for nutritional cycles and for the decomposition of natural and synthetic compounds, including pesticides
There are, only a few critical studies of the soil microbial activity affected by organic contra conventional cropping

Summary

Introduction

As Fitz Patrick (1986) stated, soils can be considered our major natural resource, because most of our food and clothing are derived from them directly or indirectly. In long-term experiments, Eiland (1980), Muller (1984) and Scherbakov (1984) found that organic manure increased the dehydrogenase activity and some other microbial parameters more than the equivalent amounts of inorganic fertilisers. There are, only a few critical studies of the soil microbial activity affected by organic contra conventional cropping. In the same Bavarian study, Diez and Weigelt (1986) found only slight differences in soil chemical properties; the phosphorus content was higher in conventional agriculture, and the magnesium content was higher in organic agriculture. Borchert (1986) found no clear differences in soil physical properties during the same experiment It is not clearly known whether the microbial activity is different between conventional and organic agriculture, or how soon this possible difference in microbial activity occurs after the change from conventional to organic agriculture. Agricultural methods involving a fairly stable structure preventing tightening would be useful in such types of heavy soil

Materials and methods

Findings

Discussion