Effects of Zn and P in Coffee Seedlings Grown in a Brazilian Latossol.

The antagonistic interaction between P and Zn in plants is an important issue mainly in tropical soils which have low P availability and demand high inputs of P fertilizer. It was studied the effects of soil applied P and Zn on seedlings of coffee (Coffea Arabica L. cv. Catuai) cultivared in a sandy loam Brazilian Red-Yellow Latossol at greenhouse conditions. Seedlings with four pairs of leaves were grown for 122 days in 2 dm³ pot containing soil that received Zn (0, 5, 15, and 45 mg dm^-3) and P treatments (0, 200, 600 and 1800 mg dm^-3) arranged in a 4 × 4 factorial with 3 replications in an entirely random block design. Zinc was added as Zn sulfate and P as triple superphosphate. After liming, the soil received (mg dm^-3) 100 N, 100 K, 40 S, 0.8 B, 1.5 Cu, 4 Fe, 3.6 Mn and 0,15 Mo. Water soluble Zn was determined in extracts obtained from the fresh matter of the 2^nd pair of leaves (3 g fresh tissue + 9 ml 1mmol L^-1 MES, pH 6,0; 10000 g centrifugation for 15 min) by using ICP-OES for dosage. Leaf total Zn, P and Fe were determined in the dry matter after nitric perchloric digestion. The superoxide dismutase (SOD) activity in leaves was determined. Increased P doses added to soil did not affect total Zn in leaves but higher doses of P added to soil decreased leaf soluble Zn indicating antagonistic effect of P with the Zn soluble form which is supposed to be physiologically active. With the increase of P added to soil there was increase in SOD activity, however, increased Zn doses had opposite effect lowering SOD activity. Additionally, the increase of P added to soil resulted in symptoms of Fe deficiency in the coffee young leaves.