Changes in soil structure and pore functions under long term/continuous grassland management

Abstract

Pore size distribution (PSD), and wetting/drying mechanism enable proper understanding of how land management changes influence soil structure and function dynamics as a measure for soil quality. Therefore, the objectives of this study are to: (i) estimate the soil quality index under continuous long term grassland management, and its impacts on soil hydro-physical and functional properties; (ii) differentiate the impact of the grassland age on the PSD curve structure using data obtained from soil water retention and (iii) determine the impact of wetting/drying on soil structure and functional dynamics. Soil hydro-physical, and functional properties of grassland at different ages (1, 2, 8, 13, 19 and 24 years) after renovation by plowing were determined. Data from the soil water retention curves were fitted to van Genuchten’s equation. Three (3) wetting/drying cycles were considered for grassland managed for 2, 13 and 24 years in order to detect further soil structure developments due to assumed climate change impacts. Results showed that total soil porosity and the number of coarse pores increased, while the soil bulk density decreased as sward age increases in all studied depths (0–5, 10–15 and 20–25 cm). Soils at 24 years grassland management showed the most intense changes in pore continuity by an increased hydraulic conductivity and an improved pore size distribution which both support root growth and nutrient as well as water accessibility. Notable (significant) difference in the soil hydro-physical properties occurred as early as 2years after grassland renovation, but a measurable improvement of soil functions down to 30 cm depth lasted 19 years. To test the hypothesis how far could a more intense wetting/drying furthermore enhance the restructuring we carried out extra wetting/drying experiments. It could be shown that the Ksat and air permeability values increased the more pronounced when the matric potential gradients and these cycles occurred more often. Thus, with increase in sward age and cycles these values further increased. However, the formation of macroscopic more homogenous structure can also result in higher values of Ksat and air permeability after shorter periods but the heterogeneity of the data was greater than after 24 years, in all depths. Therefore, results from our study can be used to establish a long-term sustainable grassland management without irregular soil inversion as effective strategy for improving soil structure and functionality.