Speaker
Description
Introduction: Renewable energies for sustainable and climate-neutral electricity production are on the rise worldwide. High-voltage direct-current (HVDC) transmission via underground cables gains influence to connect large production sides with consumer regions. In Germany, almost 5,000 km of new power line projects with an initial start date of 2038 or earlier are planned. During transmission, heat is emitted to the surrounding soil, but how this heat affects root growth and yield of the above crop plants is not well known and needs research.
Material & Methods: For that purpose, we designed and constructed a low-cost large HeAted soiL Monolith (HAL-M) for simulating heat flows within a natural soil composition and density. 24 HAL-Ms with a height of 1.56 m and an approximate diameter of 0.56 m were built for this experimental setup. Each contained approximately 400 kg of soil, with a planting area of 0.177 m2. The foundation of the twelve HAL-Ms was a barrel roller (HBR10, Hillesheim), equipped with a built-in heater. The HAL-Ms were filled with natural top- and subsoil extracted from two different sites near Bernburg and Merseburg (Germany, Saxony-Anhalt), representing the two different regional soil types 12x LOESS and 12x SAND as factor SOIL. For the factor TREATMENT, half of the HAL-Ms with LOESS and half of SAND were heated with constant 50° C (6x HEAT), and the other served as the control group (6x CTRL). For the factor RAIN, three levels (2x DRY 407 mm, 2x MID 528 mm and 2x WET 679 mm) were calculated based on data from 1988 to 2018 by the German Meteorological Service (DWD). We were able to observe root growth, soil temperature and soil water content over an extended time period. The plants were cultivated in three successive growth phases (GPs) simulating crop rotation. To avoid the need for vernalization, spring barley (Hordeum vulgare) GP1, sugar beet (Beta vulgaris) GP2 and spring wheat (Triticum aestivum) GP3 were cultivated.
Results: The yield of spring barley during GP1 under the SAND treatment was significantly reduced under the influence of HEAT (423.6 to 261.9 g m-2). RAIN also exerted a significant impact on the yield, with higher values under WET than under MID and the lowest yield under DRY. Moreover, HEAT reduced the yield under the LOESS treatment (without statistical certainty). In contrast to spring barley during GP1, the sugar beet yield was higher under the influence of heat emission, at least under the LOESS treatment (5609.0 to 6608.0 g m-2). RAIN imposed a significant impact on the yield, with the highest values under WET, declining from MID to DRY. There was no statistically significant difference between the CTRL and HEAT treatments for either soil type during GP3, although there was a slightly lower yield under the influence of heat emission. RAIN influenced the yield in a similar pattern to that of previous crops. There was no interaction effect between TREATMENT and RAIN on the yield during the single growth phases.
The root intensity during GP1 under simulated heat emission was significantly reduced at soil depths from 71.0 to 101.5 cm under the LOESSS and SAND treatments. In contrast to GP1, HEAT did not affect the intensity of sugar beet roots during GP2. During GP3, the root intensity at depths from 71.0–101.5 cm under the LOESS treatment was reduced under the influence of HEAT. There was a notable tendency for reduced root growth due to heat emission under the SAND treatment (p value=0.0585).
Discussion: We showed that under the simulated conditions, heat emission could reduce yield and root growth depending on crop type and soil. This experimental design can serve as a low-cost, fast and reliable standard to investigate thermal issues from cables of all kinds regarding various soil compositions and types, different precipitation regimes and several crop plants that are affected by similar projects. The HAL-M could serve as a link between pot and field trials with advantages of both and could be an enrichment for many research areas.
Figure 1: Construction of the HeAted soiL Monoliths (HAL-Ms). (a) Subsoil with black duct tape as a root barrier and two transparent tubes offset by 90°; (b) topsoil with an FDR sensor; and (c) finished HAL-Ms in the greenhouse.
| Keywords | HVDC transmission, earth cable, root growth, thermotropism, HAL-M |
|---|
