Optimization the fertilization of olive orchards in Tunisia

The project started in 2014 with the objective to increase the revenues of farmers by increasing olive production through the adoption of best fertilization management. The first activity of the project was initiated in 2014 with the development of the initial nutrient status of olive orchards in irrigated and rainfed areas of Tunisia. Leaf samples were collected in January and July 2015. Results showed that N remained at the same range in rainfed orchards. For P, a little decrease was observed from 2014 to 2015 and K concentration decreased by 50% from July 2014 to July 2015. In intensive olive orchards, 25% of the orchards were deficient in N and P; however, K was deficient in 50% of the orchards. In the super intensive system, 30% of olive orchards were deficient in N and K and 20% were deficient in P.

The second activity for the project was the assessment of the effect of foliar fertilization under saline soil conditions. This study was carried out in an olive orchard located in Northern Tunisia. The electrical conductivity of the irrigation water was 4.6 mS/cm [moderately high]. The experiment consisted of foliar fertilization with different sources of N, P, K, Ca, and B combined with two irrigation treatments: magnetic-treated saline water, and saline water. Two types of water were used for foliar fertilization: tap water and saline water.

Results showed that the use of magnetic water for irrigation did not affect either the nutritional status or the growth of olive trees. Indeed, no significant difference was observed when comparing irrigation with saline water and irrigation with magnetic saline water. Foliar fertilization significantly increased vegetative growth and fruit set as compared to the farmer fertilizer practice (FFP). The water quality used for foliar fertilization (tap water or saline water) had no significant effect on growth parameters. Foliar fertilization mainly by using tap water leads to a decrease in leaf sodium content, under the critical concentration for this toxic element (2000 ppm) as compared to foliar fertilization using saline water and FFP.

The third activity of the project was to study the nutritional balance of four super high-density olive orchards in Tunisia by the use of three methods: the critical concentration, the DOP (Deviation from the optimum percentage) and the binary relationship. To develop the DOP and the binary relationship methods, foliar diagnosis was undertaken in four SHD olive orchards located at Mornag (North), Sminja (Center), Sfax (South-East) and Gafsa (South-West). Results of this activity are in progress.