Effectiveness of calcined rock phosphate and leucaena prunings as a source of nutrients for maize in a tropical soil

Cost reduction and an increased efficiency in the utilization of nutrients are essential for establishing agricultural systems in the tropics. The combined effects of calcined Al phosphate (ALP) and leucaena prunings (L) on the agronomic efficiency and on the efficiency of physiological use of nitrogen (N) and phosphorus (P) in maize were assessed. The treatments consisted of 160 kg ha⁻ ¹ of P₂O₅ from ALP and 100 kg ha⁻ ¹ of N from urea (ALP+U); 160 kg ha⁻ ¹ of P₂O₅ from ALP and 6 Mg ha⁻ ¹ of L (ALP+L); 160 kg ha⁻ ¹ of P₂O₅ from single superphosphate (SSP) and 100 kg ha⁻ ¹ of N from U (SSP+U); 160 kg ha⁻ ¹ of P₂O₅ from SSP and 6 Mg ha⁻ ¹of L (SSP+L); and a control without fertilization. The decreasing order of effectiveness among treatments was SSP+L > ALP+L > SSP+U > ALP+U > control. Both leucaena–phosphate combinations had beneficial effects on the growth of the maize, the N and P recovery, and the agronomic efficiencies. Both ear weight and grain weight were higher under the SSP+L treatment than under the SSP+U treatment and higher under the ALP+L treatment than under the ALP+U treatment. The low N and P agronomic efficiency in maize grown under the ALP+U treatment made the combined use of these fertilizers undesirable. The satisfactory efficiency of grain production shown by the maize grown under ALP+L indicated that this treatment could replace processed fertilizers for use in agrosystems management in the tropics.