Short-term changes in soil pore size distribution: Impact of land use

Soil pore characteristics and the fate of new switchgrass-derived carbon in switchgrass and prairie bioenergy cropping systems

Monoculture switchgrass and restored prairie are promising perennial feedstock sources for bioenergy production on the lands unsuitable for conventional agriculture. Such lands often display contrasting topography that influences soil characteristics and interactions between plant growth and soil C gains. This study aimed at elucidating the influences of topography and plant systems on the fate of C originated from switchgrass plants and on its relationships with soil pore characteristics. For that, switchgrass plants were grown in intact soil cores collected from two contrasting topographies, namely steep slopes and topographical depressions, in the fields in multi-year monoculture switchgrass and restored prairie vegetation. The 13C pulse labeling allowed tracing the C of switchgrass origin, which X-ray computed micro-tomography enabled in-detail characterization of soil pore structure. In eroded slopes, the differences between the monoculture switchgrass and prairie in terms of total and microbial biomass C were greater than those in topographical depressions. While new switchgrass increased the CO2 emission in depressions, it did not significantly affect the CO2 emission in slopes. Pores of 18-90 µm Ø facilitated the accumulation of new C in soil, while > 150 µm Ø pores enhanced the mineralization of the new C. These findings suggest that polyculture prairie located in slopes can be particularly beneficial in facilitating soil C accrual and reduce C losses as CO2.

Influence of antecedent soil moisture content and land use on the surface runoff response to heavy rainfall simulation experiments investigated in Alpine catchments

In small Alpine catchments, floods are mostly triggered by surface runoff generation during convective heavy precipitation events. Their magnitude also depends on the antecedent soil moisture content, which was shown in several previous studies. This study aims at understanding (a) which sites change their surface runoff response to rainfall events with high precipitation intensity under very moist pre-conditions to what extent and (b) on which site characteristics this depends on. Therefore, we conducted repeated rainfall simulation experiments (40-80 m2, 1 h, 100 mm h-1) at 20 sites in five Eastern Alpine areas and analyzed their results on the basis of soil-physical parameters derived from collected soil samples. The hay meadow sites reacted with a strong increase in surface runoff to reduced saturation deficits, the pasture sites showed a smaller but visible response. The forest sites had the highest water retention capacities. The change in the surface runoff response is a function of the saturation deficit at the beginning of the initial experiment (r = -0.58). The soil physical parameters, especially the fine pore fraction (r = 0.56), correlate with the difference of the total surface runoff coefficient between the initial and the repeated experiment. The fine pore fraction also shows a high correlation (r = -0.78) with the saturation deficit at the beginning of the initial experiment, although pores of this fraction were saturated during all experiments. (Non-quantifiable) Land use effects, which in turn influence the soil physical parameters, play an important role in explaining how the surface runoff response in the repeated rainfall simulation experiment differs from the initial experiment. The information on land use and soil characteristics allowed the sites to be categorized into four types in terms of surface runoff disposition and the increase in total surface runoff coefficient in the second rainfall simulation experiment.

Intra-Soil Milling for Stable Evolution and High Productivity of Kastanozem Soil

The long-term field experiment on the Kastanozem showed that the standard moldboard plowing to a depth of 22 cm (control), chiseling to a depth of 35 cm, and three-tier plowing (machine type PTN–40) to a depth of 45 cm was incapable of providing a stable soil structure and aggregate system. The transcendental Biogeosystem Technique (BGT*) methodology for intra-soil milling of the 20–45 cm layer and the intra-soil milling PMS–70 machine were developed. The PMS–70 soil processing provided the content of 1–3 mm sized aggregate particle fraction in the illuvial horizon of about 50 to 60%, which was 3-fold higher compared to standard plowing systems. Soil bulk density reduced in the layer 20–40 cm to 1.35 t m−3 compared to 1.51 t m−3 in the control option. In the control, the rhizosphere developed only in the soil upper layer. There were 1.3 roots per cm2 in 0–20 cm, and 0.2 roots per cm2 in 20–40 cm. The rhizosphere spreads only through the soil crevices after chilling. After three-tier plowing (PTN–40), the rhizosphere developed better in the local comfort zones of the soil profile between soil blocks impermeable for roots. After intra-soil milling PMS–70, the rhizosphere developed uniformly in the whole soil profile: 2.2 roots per cm2 in 0–20 cm; 1.7 roots per cm2 in 20–40 cm. Matric water potential was higher, soil salinization was lower, and the pH was close to neutral. Soil organic matter (SOM) content increased to 3.3% in 0–20 cm and 2.1% in 20–40 cm compared to the control (2.0% in the 0–20 cm soil layer and 1.3% in the 20–40 cm layer). The spring barley yield was 53% higher compared to the control. The technology life cycle profitability was moldboard 21.5%, chiseling 6.9%, three-tier 15.6%, and intra-soil milling 45.6%. The new design of the intra-soil milling machine provides five times less traction resistance and 80% increased reliability, halving energy costs.