How respond soil organisms to soil tillage systems?

Background and Objective

Based on the general strategy to conserve biodiversity and the ecosystem services provided by organisms, it was the aim to assess the functional and structural biodiversity in arable soils considering the impact of different tillage systems. Up to now, a respective synopsis was missing for Germany.

Target Group

Science community, public services, consultants, policy makers, farmers

Approach

A survey on scientific literature was conducted, which has been published during the past six decades. The state of knowledge was analyzed covering the impact of conventional and conservation tillage as well as direct drill on soil biota in arable soils. Besides abundance and biomass of soil organisms, species richness and individual densities of taxonomical and functional units (ecological groups, life history traits, feeding guilds) were evaluated. Furthermore, infestation rates of soil borne pathogens, various quotients, which are indicating soil processes controlled by microbial activity, and enzyme activities were included in the analysis.

Data and Methods

In total, 162 papers in scientific journals, conference proceedings, reports and PhD theses published in the years 1950-2010 were screened for data on effects of soil tillage on soil biota. Based on selection criteria like number of treatment replicates, discrimination of tillage effects from other treatment effects, clear data presentation and provision of data on soil conditions, cropping and management only 74 papers representing effects of tillage intensity on soil fauna and 28 papers focussing on effects on microorganisms and microbial activity were included in the evaluation. All data were statistically analysed.

Our Research Questions

How do soil tillage systems of different intensity affect soil biodiversity? What does this mean for the functions, which different groups of organisms fulfill? What can be concluded for best Praxis?

Results

The results were obtained within a wide array of indicators covering different functional groups of soil biota. Soil fauna and soil microorganisms respond specifically to tillage systems depending on soil texture, crop and crop rotation.

Earthworms show significantly higher individual densities under conservation tillage and even more under direct drill compared to conventional tillage. Furthermore, the species diversity within the earthworm community is increasing with decreasing tillage intensity. Additionally, the microbial biomass is higher under reduced tillage systems. Contrary, direct drill characterized by the lowest intensity has adverse effects on enchytraeids and nematodes. It is assumed that both soil fauna groups benefit from lower tillage intensity without turning the soil but they need a minimum of soil loosening like conservation tillage does. This fact is even more pronounced in case of mites and collembolans. Their abundances are highest under conventional tillage and lowest under direct drill. One reason may be that many species are unable to burrow through the soil; however, they depend on an extensive pore system to live in. Conventional tillage meets this requirement best rather than any other.

Furthermore, the results show that a reduction in tillage intensity does not necessarily promote an infestation impact by soil-borne pest organisms as often assumed. The increase of antagonistic species causes a decrease of phytopathogenic soil organisms in many cases.

Soil biota does not only respond to tillage intensity but also to texture-tillage interactions. Consequently, it is also a question of specific site conditions whether a tillage system affects soil biodiversity positively or negatively. Against this background, local site conditions like soil texture should be considered within a decision process of choosing the adequate tillage system for a given site.