Influence of phosphorus and sulfur nutrition on composition ofClitoria ternatea L.

Summary A greenhouse experiment on a silt loam surface soil (Typic Hapludult) was done to investigate effects of P and S on yield, quality aspects and sugar reserves in the tropical forage legumeClitoria ternatea L. Four levels of P and two N treatments (NH₄NO₃ vs symbiotic) were arranged in a factorial design with four replications. After the first cutting two levels of S were imposed on this design.Phosphorus enhanced dry matter yield in the first cutting. Its effect was smaller in the second cutting. Amount of P required to produce maximum plant yield dropped from 200 mg/kg soil (or more) at the first cutting to 50–100 mg/kg at the second. Added S improved growth at suboptimal levels of P. At optimal P and S, symbiotic and +N plants yielded alike.Phosphorus and S fertilization caused several changes in plant composition. Nitrogen concentration was raised by S treatment and lowered by P. Combined addition of P and S lowered plant nitrate content. In symbiotic plants, soluble sugar concentrations were higher than in N-treated plants, and were increased by P and S treatment. In N-treated plants, neither P nor S increased reducing sugar concentration, but they increased total sugar.