The influence of phosphorus and calcium application rates on the mineral composition of the perennial legume Macrotyloma axillare

The response of legumes to the supply of either phosphorus (P) or calcium (Ca) alone has been extensively investigated but no prior studies have evaluated their combinations in the perennial legume Macrotyloma axillare (Macrotyloma legume). This study assessed the mineral composition of Macrotyloma legume in response to the combined application of P and Ca in an Ultisol. The experiment was conducted in a greenhouse in Nova Odessa city, Sao Paulo, Brazil. Five rates of P and Ca, respectively, were combined in a 5(2) incomplete fractional factorial design. Thus, the treatments consisted of 13 P and Ca combination rates (respectively, in mg dm(-3)): 0-0, 0-40, 0-80, 15-20, 15-60, 30-0, 30-40, 30-80, 45-20, 45-60, 60-0, 60-40 and 60-80 arranged in a randomised block design with four replications. Mineral composition was evaluated after two harvests (53 d after sowing and 34 d after the first harvest). During the initial growth of the Macrotyloma legume, P x Ca interactions occurred. The P supply antagonistically influenced the nitrogen content. The excess P supply reduced nitrogen accumulation in the shoots and caused a lack of nitrogen in the leaves. The Ca supply synergistically impacted the magnesium content and caused a 'Viets effect' in potassium content.