| Abstract: | Basic effect of phosphorus fertilizers To test the basic effects of Thomas slag (Basic slag), Rhenaniaphosphate, Superphosphate, Hyperphos (soft rockphosphate) and Novaphos (partly water soluble phosphate), model, pot and longterm field trials were carried out. Changes in soil pH and base saturation served as a measure of the basic effect. The basic effect results from chemical reaction (oxides, hydroxides, carbonates and silicates of alkali- and earth alkali components as well as Ca-phosphates) and physiological reaction (different uptake of P and Ca by plant roots in exchange with HCO and H+). In contrast to Thomas slag and Rhenaniaphosphate the basic effect of Hyperphos due to chemical reaction is small; Superphosphate and Novaphos both have a chemically acidic reaction. Plant growth increased the basic effect of all fertilizers, especially of Hyperphos. On acid and weakly acid soils (field and pot trials), Hyperphos achieved about the half effect of Thomas slag expressed on a total phosphate basis whereas the effects of Superphosphate and Novaphos were only poor. The basic effect of P-fertilizers is directly associated with their solubility and P-effectiveness depending on particular soil conditions (pH). In a pot trial using loamy soils with a requirement for lime and small requirement for phosphorus, Thomas slag, Rhenaniaphosphate and Hyperphos showed nearly the same basic effect (50kg CaO per 100kg fertilizer). This value contrasts with the much lower figures for Novaphos (10–20kg) and Superphosphate (0–10kg). |
