MICRONUTRIENT, MAGNESIUM AND PHOSPHORUS EFFECTS ON BIOMASS AND LEAF TISSUE NUTRIENT CONCENTRATIONS OF FIELD-GROWN LEUCAENA-LEUCOCEPHALA

To optimize biomass and crude protein (CP) production for leucaena (Le ucaena leucocephala) in southern Texas, field trials were conducted wi th treatment combinations of three levels of phosphorus (P), two level s of Mg and two levels of soluble trace element mixture (STEM). The P was banded in the soil while the Mg and micronutrient blend were appli ed to the foliage. A combination of P (22 kg ha(-1)), Mg and STEM fert ilizers significantly increased biomass from 2555 kg ha(-1) to 3028 kg ha(-1). This treatment was associated with an increase in leaf CP fro m 27.9% to 31.0%. P fertilizer had no significant effect on leaf P, bu t significantly increased leaf nitrogen (N) and leaf copper (Cu). A fo liar spray of Mg significantly increased leaf N, P, and Cu. A foliar s pray of a complete micronutrient blend increased leaf Cu. Biomass prod uction was correlated positively (decreasing order) with leaf Cu, N, a nd Mg and negatively with Zn. Leaf N was positively correlated with le af P and calcium. The critical tissue concentrations (CTC) (where 90% of predicted maximum leaf protein was obtained) were 0.18% and 4.49 mg kg(-1) for leaf P and Cu, respectively.