Changes in physical properties of a loess soil in China following two long-term fertilization regimes

A 13-year long-term experiment on the Loess Plateau of China was used to evaluate the effect of two different fertilizer regimes on the soil's physical/hydraulic properties. The fertilizer regimes included (i) control without any fertilizer (C), (ii) applications of chemical fertilizer (NPK), and (iii) applications of chemical fertilizer plus dairy manure (MNPK). Undisturbed soil cores were collected from the field to determine soil water retention curves and hydraulic conductivity (saturated and unsaturated). In addition, gravimetric water content, soil bulk density, porosity and saturated hydraulic conductivity were measured several times during the crop growing season to check seasonal variations. Annual application of manure increased soil water retention at the two soil depths tested (0-5 and 10-15 cm) relative to the control treatment (P <= 0.1), by 13 to 32% at tension ranges from 0 to 300 kPa for the 0-5 cm layer, and by 5 to 19% from 0 to 2 kPa for the 10-15 cm layer. The field soil water content was also significantly increased at 0-10 cm depth (P <= 0.05). Saturated hydraulic conductivity did not show any significant differences among treatments on the sampling dates due to large variations in the data. In contrast, the MNPK and NPK treatments decreased unsaturated hydraulic conductivity compared with C at 0-5 cm depth. No significant differences between treatments in this variable were observed at 10-15 cm depth. Generally, NPK showed similar effects to C. Soil physical properties (bulk density and porosity) showed significant seasonal variations. (c) 2006 Elsevier B.V. All rights reserved.