Reducing tillage intensity - a review of results from a long-term study inGermany

This paper reviews research performed at the Justus-Liebig-University of Gi essen, Germany into the impact of different tillage systems on soil propert ies and quality. The impact of intensive soil tillage treatments on several soil properties was described by means of selected data obtained through l ong-term interdisciplinary research. The experiments were based on comparative application (long-term, up to 18 years investigations) of the respective tillage options on different soils (e.g. Eutric Cambisol, Eutric Fluvisol) ranging in texture from sand to a s ilt loam. These soils are located at five field sites with different crop r otations in the central German state of Hesse. Tillage intensity of the sys tems was considered to decrease in the following sequence: Conventional plo ugh tillage (CT), reduced tillage (RT), and no-tillage (NT). For elucidating the impact of tillage intensity, the tillage extremes CT an d NT were compared. Physical conditions of soil as influenced by the applic ation of RT were considered to be intermediate between CT and NT. In genera l, bulk density in the upper layer of NT soils was increased, resulting in a decrease in the amount of coarse pores, and a lower saturated hydraulic c onductivity when compared with the CT and RT soils. Surface cover by crop r esidues and higher aggregate stability under NT protected soil fertility by avoiding surface sealing and erosion. Lateral losses of herbicides were al so reduced under NT conditions, whereas the susceptibility for preferential vertical transport of herbicides needs further evaluation. Accumulation of organic matter and nutrients near the soil surface under NT and RT were fa vorable consequences of not inverting the soil and by maintaining a mulch l ayer on the surface. Those improvements were associated with enhanced biolo gical activities in NT and RT topsoils. Increased earthworm activity in NT treatments was associated with a system of continuous macropores which impr oved water infiltration rates. Earthworms support decomposition and incorpo ration of straw. Soils which have not been tilled for many years were more resistant to vehicle passage; consequently, the compaction by traffic was l ower. Penetration resistance curves indicate that a uniformly stable struct ure had developed over the years in NT soils. Overall, the results show that RT and NT were beneficial to the investigate d soil properties. If crop rotation, machinery, and plant protection are we ll adapted for the introduction of conservation tillage, these systems may replace conventional ploughing systems in many cases in German agriculture. (C) 1999 Elsevier Science B.V. All rights reserved.