Comparison of Different Nutritional Diagnostic Methods for Peach Trees Treated with Iron Chelates

Synthetic chelates such as ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid) (EDDHA) have shown their efficacy in correcting iron (Fe) chlorosis on crops grown on calcareous soils. Several parameters, such as Fe concentration, soil and plant analyzer development (SPAD) index, yield, and fruit size, have been previously described to evaluate their efficacy. However, the relationships among them and the method variability are little known. The aim of this study was to examine both relative standard deviations and coefficients of correlation when several nutritional status indexes are compared. Three Fe chelates plus additional treatment without any exogenous Fe source were applied on a commercial nectarine grove during two consecutive growing cycles. Data from 12 nutritional status indexes were compared (related to Fe concentrations in leaf and flower, SPAD index, Fe / manganese (Mn) ratio, yield, and size of fruit). Relative standard deviations (RSD) (as dimensionless parameter) were statistically compared. Additionally, Pearson's correlation coefficient was analyzed by comparing mean values from all pairs of nutritional status indexes. Statistical analyses, analysis of variance, and Pearson's correlation coefficient were performed. Because several methods are used for nutritional status assessment, statistical methodology is necessary to know their dispersion and the relationships between these methodologies. In this experiment, relative standard deviations of all nutritional status indexes were less than 30%, which is associated with acceptable experimental variability. In conclusion, SPAD index in fruit-bearing branches seems to be one of the most adequate nutritional evaluation method because low RSD and no variation throughout sampling time and growing cycle were found. However, Fe content in leaves at 77 DAFB (days after full bloom) was correlated with yield and quality fruit parameters having relevant significance as prognosis parameters. In addition, Fe contents in leaves show low relative standard deviations.