A Comparative Study on the Effect of Water and Citrate Soluble Phosphatic Fertilizers on Yield and P-Uptake on Tropical and Subtropical Soils

In Germany as well as in other Western European countries very early the question about the efficiency of the various forms of phosphate fertilizers was investigated, The investigations have proved that not only fertilizers containing water soluble phosphates show a good response to the yields of the plants, other forms of phosphate which are soluble in citrate or citric acid (i. e, DCP) may have adequate results too. Moreover, the investigations have shown that Rhenaniaphosphate soluble in ammonium citrate acid has a better fertilizing effect than superphosphate on acid soils as well as on calcareous and alkaline soils.

During the last years, similar investigations on tropical soils were conducted especially in India. Results from other tropical countries are only sporadically available. On various lateritic soils in Kenia and Liberia etc., the citrate soluble phosphate had better effects than the water soluble forms. This was the case especially on soils with a low pH value. Pot experiments with two alluvial soils from the western region of Turkey (pH more than 7) and two from Ethiopia (pH 5.1 & 4.1) showed similar results. The effects on the yield of the two forms-water soluble and citrate soluble phosphates-were adequate on all soils. On Ethiopian soils the P-uptake from the citrate soluble phosphate was higher than that from water soluble phosphate.