Leaf Phosphorus Diagnosis of Sugarcane on Organic Soils

Most of the sugarcane (interspecific hybrids of Saccharum sp.) production in Florida is on organic soils. Supplemental phosphorus (P) fertilizer is often applied for optimum yields, but producers are required to reduce P levels in farm drainage waters. The objectives of this study were to relate optimum leaf P tissue concentration with yield in organic soil, and to determine optimum leaf sampling dates during the summer. Eight genotypes were planted at two locations, eight additional genotypes were planted at a third location, and eight more genotypes were planted at a fourth location. Crops were grown for three years. Measurements of leaf P concentration were repeated during growth seasons and over crop years for a total of six sampling dates at each location. Three fertilizer P treatments (0, 24, and 48 kg ha−1 yr−1) were applied to all genotypes at each location. Leaf samples were partitioned into early-, mid-, and late-summer dates. Early-leaf samples had the widest range in leaf P concentrations compared with midand late-season leaf samples. Correlation analyses of yield vs. leaf P concentration across all treatments in earlyand mid-summer were statistically significant (P < 0.05), but coefficients were low (r = 0.14 and 0.26, respectively). No consistent relationship across locations described the effect of leaf P tissue concentration on yield. Leaf P concentrations could not provide accurate P fertilization rates that will give maximum sugarcane yields and prevent overfertilization of P. The highest potential for relating leaf P concentrations with yield appears to be from early leaf samples.