A well maintained soil pH will maintain the value of the soil resource.

Thanks. I was looking for any way the Ca readings may be affected. As only Ca and pH was checked within the material it's hard to find out what is actually responsible for yearly fluctuations there. Would you advise adding any more checks? I will suggest that P, N, C, Na are a must.

Seasonal fluctuations in soil chemistry commonly reflect changes in soil moisture content and associated water flux. Concentration of salts during periods of high ET and subsequent dilution during periods of low ET and rainfall infiltration. If you are close to the sea the flux of marine aerosols derived Na will drive desorption of Ca and other ions from exchange sites. Having measured temporal variation in soil water drainage the variance in conductivity and composition of soil waters can be large. Land use is important but secondary to the soil makeup and climatic drivers.

Thanks! That's what I expected. Samples in most cases were collected alongside the strandline and within a transect cutting through coastal habitats from strandline, via different dune habitats to heathland. I would adivse that further survey should also include several other factors as Ca/pH is not enough to make more accurate assumptions.

You didn't indicate how Ca was extracted, e.g. 'exchangeable' or total.  The dunes may well contain shells or shell fragments.  In the lab this CaCO3 will supply Ca into salt solutions such as NH4Cl, unless the pH is 8.5 and the solution is alcoholic.  

I think , stoichiometric  relationship  between Na and Ca in soil will very well translate into their concentration in plants , either on dry weight basis or on fresh weight basis. But again, it will depend upon the Na -exclusion or Na-accumulation property of roots of the crop.

I do believe it was total Ca. I took into account that shell fragments may contribute to previous results. I will double check with the lab how they approached this analysis. It's the first time I didn't have to do everything by myself, from collecting to analysing so I'm quite wary about possible errors. 

Luckily, Ca contant did not contribute to increase of pH in most fragile habitats within area of study - acid heathlands. In that case, I do believe that was caused due to availability of organic acids (humic, fulvic) keeping the acidity more or less constant.

Thanks Waldemar.  I'm interested to know.  If appreciable shell is present then total Ca is unlikely to vary seasonally.  If no shell, then total Ca and 'exchangeable' Ca  may be very similar and could vary seasonally in relation to the deposition of sea spray and leaching.