Regional pH in Five Agricultural Soil-Types – Associations with Temperature and Groundwater Si in Continental Finland

Abbreviations: Clay: Clays (Several Subtypes); Coms: Coarse Mineral Soils (incl. mor + sand soils); Gw – Groundwater; Incl: Including; Miner: Mineral Soils (incl. coms + silt + clays); Mor: Moraines (Several Subtypes); Mull: A Single, Main, Organic Soil-Type; Prp: Proportion; RC: Rural Center (earlier Agricultural Advisory Center); Sand: Sands (Several Subtypes), Silt: Silt (No Subtypes), Si: Silicon; Soil: Agricultural Soil ARTICLE INFO


Introduction
Dissolved silica (SiO 2 ) is known as a product carbonate silicate cycle ( )  [1]. Weathering is associated with temperature (Temp) [2], soiltype [3] and soil ageing [3,4]. Silicate slags [5] and granite powder [6] can be used for pH elevation of acid soils. Inter-regional relative pH stability during three decades (1961 -1990) and pH asso ciation with Temp and Si.gw is suggesting on pH association with soil weathering [7]. Association of pH.tot with Si.gw is interestingly mirror-like when the regions were arranged by Temp [8]. Inter-relations between soil-type pH´s, Temp and Si.gw after [7,8] need somewhat clarification. The aim of this survey is to clarify whether where the soil pH regulation (and Si availability) seems not to be associated with Si.gw [15]. . Prp variation (SD/mean, %) when coms and miner excluded was lowest in sands and mull (39 %) and highest in clays (143 %).

Associations with pH.tot
Pearson and Spearman correlations of pH.tot with pH´s of other soil-types were significantly positive (Tables 2-4).    Table 5 and Figure 1 Associations with Si.gw

Discussion
Because the main aim of this article was to assess pH variation inside mor, sand, silt, clay and mull soil-types, (Figures 1 & 6) are without proportions of peat, gyttja and mud soil-types. Practically the part between 100 and Prp. mull colums is peat (Figures 1 & 6).
pH´s of mineral soils were 0.34 -0.49 units higher than pH.mull (Table 2) (N.B. pH.peat was lower than that pH.mull, why the difference between pH.org and pH of mineral soil-types is higher).
All analyzed soil-type pH´s associated significantly with pH.tot.
( Table 3), pH.clays with lowest association. Remarkable is that pH.tot is not a golden standard, because it is a sample weighted pH mean of different soil-types, in which proportion of mineral soil-types increased (and acid organic soil-types decreased) with increasing Temp (Figure 1).

Temp and pH:
Temp associated significantly positively with pH´s, Si.gw and Prp.miner ( Figure 1) and ( . Associations with pH.mull were borderline significant (p < 0.06) and with pH.mor non-significant (Table 6). pH.mor was most "resistant" to Si.gw variation, next sensitive were pH.mull, pH.silt and pH.sands, most sensitive was pH.clays (Figures 3-5). Because of scanty number of clay soil samples and possible several sampling error in conclusion selected interpretation: "association with Si.gw seemed to increase towards finer mineral soils". Soil-type pH's (e.g. pH.mor, (Figure 2)) deviate mirror-like from trend-line with Si.gw when the regions were arranged by Temp (similarly as pH.tot in [8]).
In Fig. 3  and so increasing pH [5,6]. Dissolved silica SiO 2 or Si(OH) 4 [19] can condense and form dimers and oligomers [20]. Oligomers of Si(OH) 4 can have buffering abilities around pH 6.8 [20] (possibly in micro-milieu, too). pKa1 for carbonic acid (H 2 CO 3 ) including CO 2 (aq) is 6.3, so macroscopic pH regulation above 6.3 could be mainly regulated by carbonic acid [21]. Regional pH´s in different soil-types were associated with different measures of soil juvenility (e.g. Prp.miner -an inverse measure of humus formation [4]) and pH as such [4], as well as with regional Temp. The carbonate silicate cycle [1] could be benefited for fertilizing and liming of agricultural soils by juvenile silicates [3,5,6,22], like the mother earth has benefited during her long life.

Conclusion
Regional pH.mor, pH.sands, pH.silt and pH.clays associated significantly with pH.tot and Temp, as well as obviously with soil weathering status. pH associations with Si.gw seemed to increase towards finer mineral soils. This phenomenon is possibly related with carbon silicate cycle.