The nutrition of Leucaena leucocephala de Wit cv. Cunningham seedlings. 1. External requirements and critical concentrations in index leaves of Nirtogen, Phosphorus, Potassium, Calcium, Sulfur and Manganese

Abstract

A series of nutrient rate experiments was conducted in pots at the University of Queensland, St. Lucia, to determine the critical concentrations of N, P, K, Ca, and S for deficiency, and of Mn for toxicity, in youngest fully expanded leaves of Leucaena leucocephala cv. Cunnningham. The P, Ca and Mn experiments were conducted using both NH4NO3 and Rhizobium inoculation as the source of nitrogen, while the K experiment was studied with both NaH2PO4 and Ca(H2PO4)2 as the source of basal P. Least squares derived response functions were fitted to data from each experiment to link growth and nodulation with the critical concentrations in youngest fully expanded leaves and with the rate of nutrient application required to produce 90% of maximum yield. These were: N, 4.1% and 645 kg ha-1; P, 0.25% and 225 kg ha-' for inoculated plants, 0.2 1% and 250 kg ha-1 for N-supplied plants; K, 2.0¦/0 and 35 kg ha-1 for Ca(H2PO4)2-supplied plants, 2.0% and 180 kg ha-1 for NaH2PO4-supplied plants; Ca, 0.49% and 225 kg ha-1 for inoculated plants, 0.38% and 160 kg ha-1 for N-supplied plants; S, 0.24% and 40 kg ha-1; Mn, 325 mg kg-1 and 35 kg ha-1 for inoculated plants, 325 mg kg-1 and 55 kg ha-1 for N-supplied plants.