PETIOLAR SAP NITRATE AS A GUIDE IN THE FERTILIZATION OF STRAWBERRY

Rational fertilisation management must be founded on an objective evaluation of needs, in real time. In this context, we have stressed the value, as a diagnostic tool, of nitrate tests applied to the petiolar sap of young adult leaves. This study was carried out in a controlled environment on a double-fruiting cultivar (‘Selva’). In comparison with the traditional leaf blade analysis, the petiolar test has proved to be a more sensitive and faster indicator of the nitrogen status of the crop. It is a complement to nitrate tests (directly assimilated nitrogen) carried out on the soil (water-extracted) to evaluate the nutritive potential of the plot. It is a near instant indicator of the plant's nutritional balance, a reflection of soil supply and a physiological demand of plants which is related to the climate. Unlike blade analysis which requires the use of a laboratory, the petiolar test can be carried out on the farm at a lower cost.

The survey conducted in the field for 2 years is aimed at validating the test and developing an interpretation guide for double-fruiting cultivars (‘Selva’ and ‘Seascape’). By exploiting the petiolar test in plots representative of pedoclimatic and agronomic situations of the zone of production, we have obtained the first references presented in this article, which place the nitrogen deficiency zone between 500 and 700 mg NO₃. The nitrogen status of the plant is considered favourable for nitrate levels in the petiolar sap between 1,000 and 1,500 mg/L.

The practical conditions of application are also described.