Soil bulk density and penetration resistance under different tillage and crop management systems and their relationship with barley root growth

To study the effects of fallow and tillage on soil physical properties and barley (Hordeum vulgare L.) root growth, an experiment was conducted for several years on two soils of contrasting depth: deep, a Fluventic Xerochrept of 120-cm depth, and shallow, a Lithic Xeric Torriorthent of 30-cm depth. Subsoil tillage (ST), minimum tillage (MT), and no-tillage (NT) were compared in the deep soil and NIT and NT in the shallow soil. Bulk density (BD), penetration resistance, gravimetric water content, gravel content, and root length density were determined at several times during the year. In the deep soil, BD was lower in the fallow and crop-after-fallow plots (1.26 Mg m(-3)) than in the continuous-crop plots (1.32 Mg m(-3)). In this soil, NT showed the largest bulk densities (mean of 1.34 Mg m(-3)), followed by MT (mean of 1.27 Mg m(-3)) and T (mean of 1.22 Mg m(-3)). Larger penetration resistance was found in NT than in ST and MT in both soils soon after tillage operations. However, root length density profiles sometimes showed greater values for NT than for the other tillage systems, revealing a good soil condition for root growth under NT. Therefore, an increase in soil strength is observed under NT in the first years after its introduction that does not greatly affect root growth in well-structured soils. Fallow reduces soil strength due to the effect of tillage and natural loosening factors like drying and wetting cycles or fauna activity. This effect extends to the following crop.