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 diagnos is in this plant at nonstandard times, reference values based on maxim um yield exist for specific areas. When a diagnosis is applied with di fferent objetives other reference values are needed. It may prove usef ul 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 ri pening cultivar ''Calanda'' grafted on seedling) and 1992 (irrespectiv e of cultivar or rootstock), were used to calculate the correlation be tween concentrations of nitrogen (N), phosphorus (P), potassium (K), c alcium (Ca), and magnesium (Mg) present in leaves. The high significan ce gave rise to the following linear regression equations, which show the relationship between nutrients at the above mentioned times: N60da ys = 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 knowi ng the standard mineral content at 120 days, it should be possible to obtain reference values needed to interprete the analysis of peach lea f samples taken 60 days after full bloom. If we compare the interpreta tion of several samples, by means of the DOP index, we find a remarkab le similarity between the experimental and calculated reference values . This could lead to a new method of early diagnosis of nutritional st atus.