Dear Portia

Your soil pH is 8.0. At this pH mostly basic cations will be there but here both acidic and basic cations are there. Try to give the details of parent material and type of soil for further interpretation of your data. If possible try to analyse once again for all the cations including acidic and basic cations. Definitely the availability of P will be reduced with the presence of Ca and Al in soil. pH 8.0 and above, P will be fixed as  Ca-P. Under acidic pH Fe and Al-P fixation will be there. I agree with your Ca data at this pH. However i have doubt on your Al value at this pH. Kindly check the Al value once again for better interpretation.  Later will give the details of reclamation

Thank Doc,

I have sent the samples to be re-analysed I was also skeptical about the samples because some of them were 13000mg/kg Al. We will also be digging a profile just to get an idea of what the root growth and distribution looks like and also to get an idea of what soil form we are dealing with. I will update you of the result.

Thanks,

Kind regards,

Portia

Der Portia, I assume that maintaining and improving plant nutrition and productivity is main objective of your work. Therefore, it would good to know what results the laboratory has been provided: total or available concentrations of Ca and Al? Further, did you elucidate any effect on plant performance, e.g. reduced plant productivity, nutrient imbalances? The latter may of importance to evaluate any strategy to improve soil quality, e.g. adding fertilizer, soil amendments etc. Best Nils 

Dear Portia, 

As Nils indicated, total concentrations of elements are not very useful predictors of agronomic characteristics.  A pH of ~8 is typical of soils containing Ca/ Mg carbonate and such soils can be very fertile.  P is not typically particularly unavailable in such soils because the elevated pH depresses the sorption properties of any oxides of Fe and Al that may be present.

 At this pH the Olsen P test would be useful.

Regards,  Paul.

Portia I was wondering as were Nils and Paul the purpose of the study - it seems to be agronomic. If the lab is analyzing the soil samples as  'total' as Paul said there is limited value. For example here is the USA USGS samples 4800+ samples across the US - high pH and low pH - the Al in the  % range with a mean of 4.59%. Al is one of the building blocks of clay  so it is common through out. Ca had a mean of 0.34% and Fe was 2.19%.  See http://pubs.usgs.gov/ds/801/  I would review analytical method that attempt to look at 'Available' nutrients (e.g. AB-DTPA, DTPA, Mehlich3, and as Paul suggested Olsen - P works for Phosphorus and higher pH. I your interest is to lower the pH for Phosphorus availability the do not lower below 6. (pH ~ 6.5 is optimum ). Al toxicity from Solution Al happens at a much lower pH. A good soil fertility text should help here.

Bob

Hi Portia, The values you present look like the results of a "Total" extraction and can be very misleading. What you need is to use a common agricultural extraction method such as the Mehlich III, which will give you plant available calcium and Aluminium (the fraction that is associated with organic matter and mineral surfaces, but not the structural parts of the clay minerals), The to assess the harmful soluble aluminium you need the KCl extract. Once you have that data then we shall be able to understand the situation better. With a soil pH of 8 I would expect the KCl extractable aluminium to be nil, therefore if you have phosphate lock-up then the cause will be calcium as Tri-Calcium Phosphate.

Good point Philip , you ahve added , i agree with you . Such extractions for total , but the astonising part is the presence of Al at such a high pH , and likewise much lower Ca compared to Al , contradicting each other, still pH runs at 8.0..

This is the problem with total extracts Anoop. The Earth's crust has Al as the second highest abundance of the elements after Oxygen and this is regardless of the soil pH. In reality both aluminium and pH only have reliance to plant growth when the extraction process is gentle, simulating the natural solubility characteristics of  the root environment.

Hi Portia

After Silica, Aluminium is the most abundant element in soils. At the higher pH's > 6-7, there cannot be soluble Al. This is a frequent mistake when total Al (XRF)  or on the typical Mehlich 3 extract, soluble Al is reported. On ICP when Mehlich 3 soil extracts are analysed, the extract is not centrifuged, this allows colloidal Si to reach the torch of the ICP instrument. As the temperature is very high, the colloidal Al is ionised. This erroneous result is then reported as soluble Al by laboratories. 

Dear Portia,

I do not know in what part of the world your work is being carried out. Humid tropics or temperate region? From the pH value you are probably in the temperate or arid environment, but the Al value indicates otherwise. As indicated by some of the reviewers above the Al and Ca values seem to be at odds for the given soil. It would be expected that in the temperate regions exchangeable Al would be nil for soils with pH H2O > 5.5.. Exchangeable Al would most likely only be present in Ultisols, but in the humid tropics Ultisols and Oxisols would have high concentrations of Exchangeable Al if the pH values are less than 5.5 because of its greater solubility at that pH range. As indicated above the values of Ca and Al are probably total values. By carrying out Ammonium acetic exchangeable cations and KCl extractable Al, a clearer picture of your problem can be got. Equally, the organic matter content (1.5%) is low. Higher amounts of Organic matter would fix the exchangeable Al and render P more available.