Olive & Oil 01/10/2012

Correct management of nitrogen and other olive nutrients

Fertirrigation requires timely interventions and the right doses. Fertilization formulas vary during the season. Attention should be paid to the residual fertility too. An excess affects oil quality

Nitrogen is one of the main nutritional factors affecting plant growth and it is normally the element which is mostly needed because it gets lost through leaching, volatilization, and other processes.

Normally, doses between 80 and 200 kg per field are used yearly. A Spanish study, though, reported that at the end of the vegetative period, nitrogen quantities of the magnitude of 160 kg/ha remain in the soil, thus suggesting an excessive fertilization, which may negatively affect both productivity and oil quality. It is actually well known that an excess of nitrogen brings along an excessive vegetative stimulus, penalizing productivity.

Moreover, excess of nitrogen is negative for the environment, especially if mineral elements are distributed for fertirrigation. An experimental study verified that doses of 600 g/tree, definitely excessive, cause losses in leaching at 80-90 cm of depth only.

In addition, oil quality deteriorates, especially in terms of total content of polyphenols, bitterness degree, oxidative stability and ratio between monounsaturated fatty acids and polyunsaturated fatty acids.

Last, in the Northern regions of the Mediterranean basin, olive trees can be more easily stressed during the summer, or during a cold winter, if nitrogen fertilization was excessive during the winter and spring.

Therefore, to increase the growth, to exploit the productivity potential, and to better prepare young plants for the winter, in order to avoid a growth during the late weeks of the fall, more correct fertilization modalities should be defined.

An experimentation in Central Italy by Dr. Lodolini and Università delle Marche has identified the better fertilization formulas in function of the season of growth and phenology phases.

The nutrient ratio varied from 50:1:10 at budding, to 2.5:1:10 at veraison. Nitrogen doses applied to four year old trees varied from 60 to 120 grams. Thus, it was demonstrated that fertilization at the maximum indicated dose increased the average production of fruit per tree, without reducing the unit weight of olives.

Nonetheless, fertirrigation improves the nutritional status of plants, by increasing the availability of N, P and K during the critical phenology phases (full blossoming and fruit-set), thus avoiding an excess of nutrients in leaves, which bears the risk of nutritional unbalances. If fertirrigation is well planned, the acclimatization of plants before the winter is favored.

di Alberto Grimelli