In-situ effect of Si fertilization on Soil-plant-water relation for different soil erosion states

Crop production is affected by drought duration and severity, which become more frequent with climate change. Several studies reported the positive effect of Silicate (Si) fertilization on soil and plant water balance. However, the relation between soil type and the impact of Silicate (Si) fertilization on plant performance, as well as the underlying mechanism for water stress tolerance, is poorly understood. To investigate the effect of Si fertilization on soil-plant-water relation in different soil types, we set up a Si fertilization experiment in an arable landscape of Northeast Germany (Uckermark region, 53° 23' N, 13° 47' E) using Barley (Hordeum vulgare) at three different sites with different soil types and erosion stages: 1) Haplic luvisol (non-eroded), 2) Haplic Regesol (extremely eroded) and 3) Endogleyic colluvic regosol (deposition). 3 Kg "Aerosil 300"   are applied to the soil (~1% ASi in topsoil) compared to control plots (no fertilization), with four replicates per treatment at each site. A campaign of 2-3 consecutive days was conducted throughout the experiment period (from April to July 2022) every two weeks. During these campaigns, we measured leaf water potential, gas fluxes (CO2 and Evapotranspiration), NDVI (normalized difference vegetation index) and biomass sampling. Soil water content and temperature were continuously monitored by soil sensors planted in situ at each plot. We harvested Barley at the end of the growing season and measured each plot's plant biomass and seed production. Our data showed that Si fertilization significantly increased the soil water content in the different soil erosion stages by 2-3%. At the plant's early growth stage, the increase in the soil water content related to Si fertilization significantly affected drought mitigation, balancing leaf water potential decrease during drought. Moreover, while plant development was not generally affected by Si fertilization, germination was delayed in non-fertilized plots. However, the vegetation period in 2022 was rather wet and a drought occurred only during the early phenological development of the plant, and no significant effects of Si fertilization on plant performance were visible (leaf water potential, net ecosystem exchange, evapotranspiration, NDVI and yield) after the early stages. Thus, no lasting effect of Si fertilization on drought mitigation on Barley could be detected, as Barley recovered quickly from drought during the early vegetation stage, irrespective of Si fertilization. All things considered, Si fertilization as an approach to enhance plant tolerance during drought is more complex than previously expected. Our results suggest that the timing and duration of drought, as well as soil type, are important factors to consider.

Keywords: Si fertilization, Drought, Soil erosion, Water Stress, Soil water content, Leaf water potential, NDVI, Gas fluxes, Plant performance.