Limited effects of crop foliar Si fertilization on a marginal soil under a future climate scenario

Abstract

Growing crops on marginal lands is a promising solution to alleviate the increasing pressure on agricultural land in Europe. Such crops will however be at the same time exposed to increased drought and pathogen prevalence, on already challenging soil conditions. Some sustainable practices, such as Silicon (Si) foliar fertilization, have been proposed to alleviate these two stress factors, but have not been tested under controlled, future climate conditions. We hypothesized that Si foliar fertilization would be beneficial for crops under future climate, and would have cascading beneficial effects on ecosystem processes, as many of them are directly dependent on plant health. We tested this hypothesis by exposing spring barley growing on marginal soil macrocosms (three with, three without Si treatment) to 2070 climate projections in an ecotron facility. Using the high-capacity monitoring of the ecotron, we estimated C, water, and N budgets of every macrocosm. Additionally, we measured crop yield, the biomass of each plant organ, and characterized bacterial communities using metabarcoding. Despite being exposed to water stress conditions, plants did not produce more biomass with the foliar Si fertilization, whatever the organ considered. Evapotranspiration (ET) was unaffected, as well as water quality and bacterial communities. However, in the 10-day period following two of the three Si applications, we measured a significant increase in C sequestration, when climate conditions where significantly drier, while ET remained the same. We interpreted these results as a less significant effect of Si treatment than expected as compared with literature, which could be explained by the high CO₂ levels under future climate, that reduces need for stomata opening, and therefore sensitivity to drought. We conclude that making marginal soils climate proof using foliar Si treatments may not be a sufficient strategy, at least in this type of nutrient-poor, dry, sandy soil.

Keywords: Climate change; Ecosystem services; Marginal soil; Sustainable agricultural practices.

Fig. 1

Evolution of the actual/potential evapotranspiration ratio throughout the growing season. Red: Si treatment, black: control. The lines are obtained by a loess smoothing function per treatment per day and the grey areas correspond to the confidence interval. Every full circle represents a value of this ratio in one unit for one day. The three vertical, dashed lines materialize the three dates at which Si treatment was applied. The black, full horizontal line represents the threshold value under which plants experience water stress. Actual evapotranspiration was calculated from changes in the weight of the lysimeter at a temporal resolution of 1-min using the AWAT noise filter [31]. Potential evapotranspiration was calculated based on the Penman-Monteith equation [18].

Fig. 2

Effect of foliar Si treatment on the dry weight (DW) of each organ (a: roots, b: stem, c:leaves, d: grain, e: chaff, f: stem density) and plant density (f) of barley individual plants at harvest. The p-value was obtained using a mixed model ANOVA with crop property as the response variable, treatment as a fixed variable, and mesocosm unit as a random variable.

Fig. 3

Detailed C budget of the effect of foliar Si fertilization. Values are in g/m² and integrated over the growing season (01/03/2021-01/10/2021). Negative values indicate C sequestration (net C gain in the macrocosm) and positive values C emissions. Soil C budget was calculated in two steps: first, the net ecosystem balance was estimated by calculating the difference between incoming (CO₂–C balance, CH₄–C balance, rainwater-C) and outgoing (leachate-C, sampling-C) C fluxes. Note that the CO₂–C balance already accounts for the difference between photosynthesis and respiration. The net C balance of the soil was then calculated as the difference between plant biomass (barley, estimated based on stem density and average weight per stem; and weeds, estimated as the difference in lysimeter weight before and after weeding, corrected by water content of 10 %, found on a representative sample of weeds, by the surface area of the lysimeter to get values in g/m², and for both barley and weeds, given a C content of 40 %) and the net C balance of the ecosystem.