SOIL TESTING, FOLIAR ANALYSIS, AND DRIS AS GUIDES FOR SUGARCANE FERTILIZATION

Foliar analysis has been practiced widely in sugarcane (a complex trispecies hybrid of Saccharum) for planning and evaluation of fertilizer programs and harvest schedules. On the mainland of the USA, sugarcane farmers have traditionally relied on soil testing to plan fertilizer programs. Soil testing remains an excellent preplant practice but its reliability for the successive ratoon crops has been questioned. Results of foliar analyses are usually interpreted on the basis of the Critical Nutrient Level (CNL) approach. Recently, the Diagnosis and Recommendation Integrated System (DRIS) was introduced as an alternative approach for foliar diagnosis. The present study was conducted to evaluate the effectiveness of soil testing and foliar analysis interpreted by the CNL approach and by the DRIS as guides for sugarcane fertilization. Standard nutrient levels and DRIS norms were established for N, P, K, Ca, Mg, Fe, Mn, Zn and Cu in the top visible dewlap leaf laminae of sugarcane. Comparison of the 3 methods was conducted in 8 fields of ratoon sugarcane representing the major sugarcane soils in southern Florida [USA]. Soil samples were collected in May and leaf samples in May, July and Sept. Fertilizers were applied in May and July as indicated by each method. Foliar analysis interpreted by either method revealed a need for applying one or more micronutrient(s) to all ratoon sugarcane in Florida. Application of N was also recommended for the 1st time on Torry muck soil (euic, hyperthermic Typic Medisaprist) by foliar analysis using both methods. Fertilization according to the DRIS significantly increased both cane and sugar yields compared with those obtained when fertilization was guided by foliar analysis using the CNL approach or soil testing. Differences were not significant between foliar analysis using the CNL approach or soil testing. The high cane and sugar yields obtained by DRIS-guided fertilization were attributed to the better nutrient balance as revealed by DRIS indices late in the season. Foliar analysis using the DRIS proved to be a better guide for fertilization of sugarcane than the soil testing method currently in use.