Changes in some soil properties in a Vertic Argiudoll under short-term conservation tillage

The purpose of this work was to determine whether some soil physical and chemical properties. and microbial activity were affected by two conservation tillage systems in a Chernozemic clay loam soil (Vertic Argiudoll), after 5 years of trial initiation. Two crop sequences, com (Zea mays L.)-wheat (Triticum aestivum L.)/soybean (Glycine max (L.) Merr.) and wheat/soybean, under chisel plowing (ChP) and no till (NT) were evaluated. Physical and chemical properties were also analyzed taking the same soil without disturbance as reference. The Henin instability index (HI) was larger in ChP than in NT in both corn/-wheat/soybean (C-W/S) and wheat/soybean (W/S) sequences (P less than or equal to 0.05). The C-W/S sequence differed from W/S (P less than or equal to 0.01) in total organic carbon (TOC). As regards organic carbon fractions, no differences were found in labile organic carbon (LOC), while W/S under ChP showed the lowest value (P less than or equal to 0.01) of humified organic carbon (HOC). No differences were found in microbial respiration either in crop sequences or in tillage systems. Soil physical and chemical properties differentiated crop sequences and tillage treatments from the undisturbed soil when a Student's t-test was performed. Five years elapsed since the beginning of this trial was time enough to detect changes in some of the soil properties as a consequence of management practices. An important reduction in the soil structural stability was observed as related to the undisturbed soil. However, the C-W/S sequence under NT resulted in lower soil degradation with respect to the other treatments. (C) 2001 Elsevier Science B.V. All rights reserved.