Strontium chloride‐citric acid extraction procedure for agricultural and environmental purposes

Abstract

The 0.02 M SrCl₂‐0.05 M citric acid solution (Sr‐citrate) has been developed to provide information about the fate of N and of other elements for agricultural and environmental soil‐testing purposes. The objective of this study was to relate the amounts of NO₃ ⁻ NH₄ ⁺, K, Ca, Mg, SO_4, B, Zn, and Mn extracted by the Sr‐citrate procedure to amounts of these elements extracted by standard procedures used in soil testing programs. The amounts of NO₃ ⁻ and NH₄ ⁺ extracted by the Sr‐citrate solution were closely related to the amounts of these ions extracted by 2 M KCl. Sr‐citrate extracted more K, Ca and Mg than 1 M NH₄OAc or Mehlich 3 in soils with CEC of less than 15 cmol_c kg⁻¹ and desorbed less K and Mg in higher CEC soils. However, the amounts of K, Ca and Mg extracted by the three procedures were very closely related to one another (r >0.93**).

The Sr‐citrate solution extracted a much larger average amount of SO₄ than 0.1 M Ca(H₂PO₄)₂. Close relationships were found between the amount of Zn (r = 0.89**) and Mn (r = 0.91**) extracted by Sr‐citrate and Mehlich 3. The amount of Sr‐extractable B was larger than but not significantly related to hot water‐extractable B. The highly significant linear relationships between the amounts of N, K, Mg, Ca, Zn and Mn extracted by Sr‐citrate and amounts extracted by standard procedures indicate that Sr‐citrate could easily be adapted to establish the fertlizer requirements of crops and identify soils with excess residual N for environmental purposes.