QUANTIFICATION OF THE EFFECTS OF OVER 35 YEARS OF INTENSIVE CULTIVATION ON FOUR SOILS

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Abstract
Soils ranging in texture from loamy sand to clay that had been tilled annually for at least 35 yr were compared with adjacent unfilled soils. Properties considered important to plant growth were measured: water-stable aggregate size distributions, bulk density (BD), organic carbon (OC), penetrometer resistance (PR), oxygen diffusion rates (ODR), pH, hydraulic conductivity (Kaep), air-filled porosity (AFP), total porosity (TP), degree of air occupation of pores (AFP/TP) and soil moisture desorption curves. AFP, AFP/TP, ODR, BD, Kaep and soil moisture desorption curves suggested that the tilled sites in all soil types had become compacted below 10-cm depth relative to the undisturbed sites. OC, PR, BD and aggregate size distributions were strongly influenced by soil textural differences. OC appeared to increase with cultivation in sandy soils compared with the undisturbed. PR was increased by tillage in the coarse-textured soils, but decreased in the fine-textured soils. Acidity increased under long-term tillage in all soils except the clay. Large degrees of variability of ODR data require further investigation. Rapid in situ techniques for measuring Kaep and AFP are needed, as these parameters appeared to best reflect the effect of long-term tillage on soil physical quality. Key words: Soil structure, soil degradation, soil compaction, soil management, tillage effects