Effect of nitrogen and magnesium application on yield and leaf-N and Mg concentrations of olive trees cv. picual

A field experiment was installed in an unirrigated olive grove of cultivar Picual, planted in 1987 on a calcaric regosol in the Portuguese Region of Ribatejo. The study was performed in order to evaluate the influence of nitrogen and magnesium fertilization on the fruit-yield, some fruit quality parameters and nitrogen and magnesium concentrations of the leaves. Three levels of nitrogen (0, 60 and 120 kg.ha(-1) N) and magnesium (0, 30 and 60 kg.ha(-1) MgO) were used, arranged into a factorial experiment with three replications. Nitrogen and magnesium were applied annually to the soil since 1995, as ammonium sulphate and magnesium sulphate, respectively. Leaf-samples were collected from the middle of the current season's terminal shoots, in July and the following January. The present paper reports the first set of experimental results, referring to the period from 1995 to 1997. Experimental results show that fruit-yield, fruit-mean weight and fruit-fat content were not significantly (p>0.05) affected by nitrogen and magnesium fertilization. A significant mean effect (pless than or equal to0.01) of the interaction between nitrogen and magnesium fertilizers on leaf-N concentration in January of 1996 was found. Increasing application rates of nitrogen led to greater leaf-N concentration, except in July 1996, although not affecting leaf-Mg concentration. The latter was not affected by magnesium supply.