Regional K buffer in organic and mineral soils and their associations with estimated cation exchange capacity, pH, groundwater silicon and some environmental factors in continental Finland 1986-90 with discussion on inorganic carbon

Cation exchange capacity (CEC) is the total capacity of a soil to hold exchangeable cations. It influences the soil’s ability to hold onto essential nutrients and provides a buffer against soil acidification. Organic matter has a very high CEC. Anyhow potassium buffer power is known to be weak in other than clayey and silt soils, especially in peat, why fertilization can cause excessive variation in plant mineral composition. Finnish soil samples are collected mainly in autumns. That’s why they obviously reflect K buffer power of organic soils, too. The aim of this study is to clarify regional associations of cropland K, (estimate) CEC (Ca+Mg+K) and pH, in organic (org) and mineral soils (min), groundwater (gw) silicon (Si) and geographic factors Latitude (Lat) and Longitude (Long). The data are from old sources.


Introduction
Cation exchange capacity (CEC) is the total capacity of a soil to hold exchangeable cations [1]. The main ions associated with CEC in soils are the exchangeable cations calcium (Ca 2+ ), magnesium (Mg 2+ ), sodium (Na + ) and potassium (K + ) [2]. Because the number of other ions than Ca, Mg and K is small, the equivalent sum of (Ca+Mg+K) can be used as a practical estimate for CEC in Finland [3]. In general, organic matter increases CEC [1,4]. Anyhow in Finland potassium buffer power is known to be weak in other than clayey and silt soils, especially in peat, why fertilization can cause excessive variation in plant mineral composition [5]. Soil samples included in this study have been collected mainly in autumns [6].
So, the autumnal K values are thought to reflect the K buffer power of the regional soils. The aim of this study is to clarify regional associations of cropland K, (estimate) CEC (Ca+Mg+K) and pH from organic (org) and mineral (min) with each other and groundwater (gw) silicon (Si) as well as with combined geographic factors Latitude (Lat) and Longitude (Long).

Materials and Methods
Data on Si.gw are from Groundwater database © Geological Survey of Finland 2017 [7]. Soil values per Rural Centers (RC)earlier ' Agricultural Advisory Centers' -from period 1986-90 are provided by Viljavuuspalvelu Eurofins Oy [8], as in [9]. Data on area of arable land (under cultivation) and borders of RC's are from Official Statistics of Finland [10] as in [9] (N.B. in [9] Si est3 is erroneous).
Values for (combined) Uusimaa and "combined" Varsinais-Suomi are attained by weighting parameter values with arable land areas.

Discussion
In 1986-90 regional K, CEC and pH values in organic and mineral agricultural soils and K.(org/min) from continental Finland were significantly associated with each other and regional Si.gw (Table 3), and so obviously with regional weathering rate. This is in concordance with old texts: CEC is an inherent soil characteristic and is difficult to alter significantly [1,12]. Ostrobothnia " (16).
Österbottens Svenska" RC was excluded because of statistical deviation. (This deviation was obviously not earlier reported). This increased Si.gw associations with other parameters including CEC (can be calculated by data in Table 1). Anyhow even median of Si.gw in " (16). Österbottens Svenska" (1.10) was higher than Finnish provincial mean (0.94) ( Table 2).
Microbiological procedures are obviously important for silicate weathering, e.g. [17,18]. Silicate fertilizers (big amounts) in dry soil can work anyhow as cationic adsorbents [19]. It has been suggested that systems draining soils (streams) with greater cation exchange capacity release more CO 2 to atmosphere than those draining poor soils based on observation that silty stream was more supersaturated than sandy stream, at approximately an order of magnitude more saturated than atmospheric equilibrium [20]. Possibly this is only sign of higher C sequestration [15] in silty stream, which obviously contained more Si.
In general, most gramineous plants (e.g. ryegrass, wheat, triticale, sorghum, rye, corn and barley) are known as Siaccumulating species [21]. Possibly mainly for this reason plowing (after some years of grass cultivation) seemed to increase plant silicon content [9], when the accumulated Si is liberating from debris to soil and plants.
In the Figures of [22] it seems impossible in Finland to reach the target pH-level 6.1 in coarse mineral soils of Lapland. Maximal yields have been obtained e.g. by winter wheat even at pH-level 5.7 [23] Possibly oligomers of condense Si(OH) 4 , with pK 6.8 of its silanol (Si-O-H) groups on the outside of oligomers is [23], can work as a buffering agent in agricultural soils. Studies on silicates as liming agents are suggested: Maximal yields can be attained by different fertilization ratios and in different pH levels in Si supplemented than in Si exhausted soils.
By improving water control via reduction of transpiration [25] Si could even rejuvenate eroded soils. Soil CEC associations with Si (Table 3), i.e. nutrient and retention, could possibly be explained by Si(OH) 4 polymers [26], which can support the water control, too. Old studies have suggested on the role of silicates as fertilizers [27]. In the future they can have an increased role as liming agets (by reducing the carbon loss via carbonate liming agents) and as carbon scavengers in general.
PS. In calculations CEC values included one decimal, but in Table 1 values are given without decimals because of scanty space.

Conclusion
In continental Finland regional Si.gw -obviously associated with weathering rate -explained significantly variation in K.org, K.min, K buffer, CEC.org, CEC.min, pH.org, pH.min, K.(org/min) and CEC.(org/min). Association of Si.gw with soil inorganic carbon is discussed.