A simplified extraction schema to for the analytical characterization of apple orchard soils

Purpose

Standardized procedures for agricultural soil analysis use different extractant solutions, to determine one or just a few elements, which needs a lot of time and manpower. Within this work, it was tried to substitute traditional methods by the use of multi-element determination techniques, like inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) applied to a few solutions.

Material and methods

ICP-OES and ICP-MS have been applied to a sequence of extracts obtained with 0.16 M acetic acid and 0.1 M oxalate buffer pH 3, which are more suitable for the plasma than traditional salt extractant solutions. Dilute acetic acid should characterize exchangeables plus carbonates, and oxalate buffer the pedogenic oxides. Aqua regia extractions in glass have been replaced by pressure digestion with KClO₃ in dilute nitric acid, which yields results equivalent to aqua regia, and additionally permits the determination of total sulfur, as well as acid-leachable boron and silicon. Total digestion was done in PTFE beakers by fuming with HNO₃/HClO₄, subsequently with HF, and final uptake in 1?+?1 HCl.

Results and discussion

The method was applied to 44 soils from apple orchards of different soil types and climatic zones. P and K obtained from standard acetate-lactate extract as well as B obtained from the Baron extract correlated with the results from the acetic acid extract better than 0.9. Just Mg from the CaCl₂ extract (Schachtschabel) was independent from all other Mg fractions. The results of the total digests could be verified by XRF analysis of the solid, Ti recovery was the most critical item. The results for Ca, Cu, Mg, Mn, Sr, Pb, and Zn obtained from KClO₃ digest and from totals, were strongly correlated. Factor analysis showed that the fraction mobilized by dilute acetic acid contained Ca-Mg-carbonates as well as Al-Ba-Na in the first factor, K-P-S in a second, whereas Mn-La-Li formed a group of its own. The pedogenic oxides, obtained from Al-Fe-Mn-Ti released in oxalate, carry most of the cationic trace elements, whereas the anions P-S-B-Si and the essentials Cu-Mo form different groups. Among the main elements, the quasi-total data were much less intercorrelated than the totals. The rare earth elements formed a strongly intercorrelated group as well after total digestion as in the oxalate leach.

Conclusions

The proposed method permits to obtain information about common cations including trace elements, and the nonmetals phosphorus, silicon, sulfur, boron, and iodine simultaneously, which could be a gate to find new relations among them. The two-step procedure permits to predict availabilities in shorter and longer periods of time. Data from the extract in dilute acetic acid for K, P, and B can substitute traditional methods of soil analysis.