Abstract
Magnesium (Mg) is an essential element for plant growth and human health. Its availability and spatial distribution in soils depends on a wide variety of intrinsic and extrinsic factors. Understanding how Mg availability changes in space and time is crucial for preventing potential deficiencies. In 1987, a soil-monitoring network (FRIBO) was launched in the canton of Fribourg, Switzerland. It was based on 250 sites distributed evenly throughout the canton so as to include a large variety of soil types (Cambisols, Gleysols, Rendzinas, Regosols, Lithosols, Luvisols and Fluvisols) under three different land use types (croplands, permanent grasslands and mountain pastures). The aim of this research was to characterize the spatial and temporal variation of total and available forms of Mg in the agricultural soils of the canton of Fribourg and to discuss potential implications for Mg fertilization management. Total Mg concentration (MgT) averaged 5.5 g kg−1, with small differences between land use types. Spatial distribution of MgT showed higher values on the southern part of the study area, mostly on Rendzinas and Cambisols. Average concentrations of available Mg forms were significantly different according to extraction methods, with water extraction (MgH2O) having the lowest value (14.2 mg kg−1) followed by calcium extraction (MgCaCl2, 109.4 mg kg−1) and ammonium acetate + EDTA extraction (MgAAE, 148.7 mg kg−1). On average, permanent grasslands had significantly higher values for all Mg forms compared to croplands and mountain pastures, a result further corroborated by the analysis of spatial distribution. Intrinsic factors, such as soil type and terrain attributes, appeared to have a major influence on total Mg content, whereas available Mg forms depended mostly on extrinsic factors, such as land use type. Temporal analysis of soil available Mg forms revealed an overall increase between 1987 and 2016, especially after a land use change from croplands to permanent grasslands. In the light of the essential role of Mg for plant growth and development, as well as its critical role in animal health, the status of Mg should continue to be monitored in the FRIBO network and plant analysis should be implemented.
Highlights
IntroductionMagnesium (Mg) is a vital element for plant growth being involved in various critical metabolic and physiological functions, such as chlorophyll and protein synthesis, enzyme activation, phosphorylation, photosynthesis and carbohydrate partitioning (Cakmak and Yazici, 2010; Farhat et al, 2016; Hawkesford et al, 2012; Marschner, 2012)
Except for the base saturation cation-exchange capacity (SatCEC), all general physicochemical properties were significantly different for the different categories of land use (Table 1)
Total Mg was more abundant in the lower mountainous portion of the canton, while the available forms of Mg were more abundant in the central region dominated by permanent grasslands
Summary
Magnesium (Mg) is a vital element for plant growth being involved in various critical metabolic and physiological functions, such as chlorophyll and protein synthesis, enzyme activation, phosphorylation, photosynthesis and carbohydrate partitioning (Cakmak and Yazici, 2010; Farhat et al, 2016; Hawkesford et al, 2012; Marschner, 2012). Mg has come into the spotlight as a limiting factor in crop productions subjected to continuous fertilization solely based on nitrogen (N), phosphorus (P) and potassium (K) (Cakmak and Yazici, 2010; Jayaganesh et al, 2011) This issue has become critical especially in more developed countries due to associated human health concerns (Guo et al, 2016; Long and Romani, 2014). The availability of Mg for plants depends on the type of parent material as well as on weathering, fixation, erosion, leaching beyond the root zone, soil moisture and soil pH, high use of NPK fertilizers, and other anthropogenic activities (Guo et al, 2015, 2016; Gransee and Führs, 2013; Metson, 1974). Mg toxicity in plants can be problematic, it is quite uncommon and its effects are often negligible (Venkatesan and Jayaganesh, 2010)
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