Influence of elemental sulfur, micronutrients, phosphorus, calcium, magnesium and potassium on growth of Prosopis alba on high pH soils in Argentina

A field trial on 3-year-old Prosopis alba growing on pH 8.5 soils in Argentina was conducted to identify mineral nutrients that were most limiting growth and to determine correlations among these nutrients. As applications of nutrients such as Zn, Cu and P would be soon rendered unavailable due to the high pH, combinations of elemental S to decrease the pH were examined along with macro and micronutrient soil additions. Thirty trees were selected with stem diameters ranging from 2.8 to 4.5 cm and divided into five treatments in a completely randomized design with 1 tree per replicate. The treatments were: (1) control, (2) addition of elemental S to lower the pH, (3) addition of S and triple superphosphate (P), (4) addition of S, P and a complete blend of micronutrients and (5) addition of S, P, micronutrients and K and Mg. Biomass increases were estimated using regression equations on stem diameter increases. A small non-significant decrease in pH of about 0.3 pH was obtained in the treatments with S, except for treatment which contained micronutrients in the form of strong base oxides. There was a significant increase in electrical conductivity due to the oxidation of the S. The best treatment containing S, P and micronutrients had a 42% increase significant biomass increase over the control. Growth was positively correlated with leaf levels (decreasing order of significance) of K, S, P, and Zn and negatively correlated with leaf Na and Ca. The leaf K, which had the highest positive correlation with growth, was highly significantly positively correlated with leaf S, P, N, and Zn and highly significantly but negatively correlated with leaf Ca, Mg and Mn. Leaf N was very highly correlated with leaf Zn, S and P concentrations. Indian workers have found that 20 years after establishment Prosopis juliflora changed the soil pH from 10.4 to 8.0. Since trees on 10 m×10 m spacings are suggested to be ultimate climax density for these ecosystems, apparently it will only necessary to add inexpensive small quantities of elemental S, Zn and K directly around 100 small trees ha⁻¹ to effect a major soil reclamation over the entire ha.