PREDICTION OF REFERENCE VALUES FOR EARLY LEAF ANALYSIS FOR PEACH-TREES

Leaf analysis of peach (Prunus persica, L. Batsch) trees is restricted to midsummer (120 days after full bloom), which is the standard time for leaf sampling of fruit trees. In order to carry out foliar diagnosis in this plant at nonstandard times, reference values based on maximum yield exist for specific areas. When a diagnosis is applied with different objetives other reference values are needed. It may prove useful to bring forward the time when samples are taken. Samples taken 60 and 120 days after full bloom for two seasons, 1987 (using the late ripening cultivar ''Calanda'' grafted on seedling) and 1992 (irrespective of cultivar or rootstock), were used to calculate the correlation between concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) present in leaves. The high significance gave rise to the following linear regression equations, which show the relationship between nutrients at the above mentioned times: N60days = 0.705N120 days + 1.557; P60days 0.181P120days + 0.244; K60days = 0.444K120days + 1.303; Ca60days = 0.386Ca120days + 0.639; Mg60days = 0.386Mg120days + 0.233. If we take these equations as a basis and knowing the standard mineral content at 120 days, it should be possible to obtain reference values needed to interprete the analysis of peach leaf samples taken 60 days after full bloom. If we compare the interpretation of several samples, by means of the DOP index, we find a remarkable similarity between the experimental and calculated reference values. This could lead to a new method of early diagnosis of nutritional status.