Biogenic silicon in agricultural landscapes (BiSiAL): Quantification, qualitative characterization, and importance for Si balances of agricultural biogeosystems

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Despite the fact that silicon (Si) is generally considered as non-essential for plants, many benefits of Si-accumulation in plants are known, e.g., increased plant growth and resistance against abiotic (e.g., water deficiency) as well as biotic stresses (e.g., fungal infections). However, several factors limit the plant available Si fraction in soils. In this context, it is of fundamental importance to analyze the size of the plant available Si fraction and corresponding influences in soils of agricultural biogeosystems in detail. Several organisms use dissolved Si (Si(OH)4) for synthesis (= biosilicification) of biogenic siliceous (BSi) structures (SiO2 x nH2O). Due to its relatively high solubility compared to minerogenic Si BSi is an important source of plant available Si in soils. Based on a combination of modern microscopic and spectroscopic methods (confocal laser scanning microscopy, micro-FTIR-spectroscopy) the quantification of single BSi pools and analyses of physicochemical surface properties of BSi structures will be realized in the requested project, objectives that cannot be obtained with established alkaline extraction methods.In general, humankind actively influences Si cycling due to intensified land use. Induced mainly by Si exports through harvesting and increased erosion the amount of plant available Si can decrease in agricultural soils (= anthropogenic desilicification). Caused by harvesting approximately up to 100 kg Si ha-1 are exported from agricultural biogeosystems every year. However, despite this knowledge, there are only fragmentary empirical findings on the subject of Si balances (status quo, Si inputs, Si outputs) of agricultural biogeosystems. Thus, the objectives of the requested project are as follows:i) Comprehensive Si balancing of agricultural biogeosystems.ii) Identification of factors that influence Si balances (degree of erosion, BSi pools, etc.).iii) Analyses of temporal developments of the plant available Si fraction and BSi pools in soils of agricultural biogeosystems.iv) Quantification of BSi pools and qualitative characterization of BSi structures in agricultural biogeosystems.The Centre for Agricultural Landscape Research (ZALF) provides worldwide unique requirements regarding the experimental infrastructure (instrumented field experiment CarboZALF-D and long-term field experiment V140) to achieve these objectives. The results of the requested project are supposed to contribute to a fundamental understanding of anthropogenic desilicification and its impacts on agricultural biogeosystems. Furthermore, practice-oriented recommendations for restriction or prevention of anthropogenic desilicification can be derived from these results.