Optimization the fertilization of olive orchards in Tunisia

This project aims to increase the revenues of olive farmers by increasing production through the adoption of best fertilization management. The first phase was initiated in 2014 with the determination of the initial status of olive orchards in irrigated and rainfed areas of Tunisia. Several olive orchards were selected in different regions and foliage were sampled in July. Results showed that N, P and K leaf contents were in the optimal range, except four samples from a rainfed olive orchard in which N and K leaf contents were lower than the threshold (adequate) value. Furthermore, leaf K concentrations were usually above the required value, in most cases greater than 1% and in some cases above 1.5%. The highest leaf K concentrations may be due to excess K fertilization or an inadequate period of sampling for K. In July, fruits still need K in preparation for fruit development during autumn. Therefore it will be more appropriate to carry out this analysis in January after the harvest.

The second phase of the project was initiated to assess the effect of foliar fertilization on olive trees under saline conditions. In Tunisia, several intensive and super-intensive orchards are located in the semiarid and arid regions where farmers tend to use saline water for irrigation. Moreover, the arbitrary use of fertilizers such ammonium nitrate will increase the electrical conductivity of fertilizer solutions. The use of foliar fertilization as an alternative to conventional fertilization may be considered to avoid the negative effect of the application of fertilizers to soil. An experiment was carried out in 2014 to study the effect of the ammonium nitrate on olive plants grown under salinity conditions (0, 50, 100, and 150 mM NaCl). Two rates of ammonium nitrate were used (i.e., 50 and 100 g). The application of ammonium nitrate to plants grown under saline conditions increased the electrical conductivity for all treatments. Fresh weight and leaf surface area were decreased by increased salinity. The beneficial effect of the application of ammonium nitrate was only found in the case of control plants (0 mM NaCl) receiving 50 g of ammonium nitrate, where fresh weight of root, shoots and leaves increased respectively by 15%, 95% and 59% compared to the control (0 mM NaCl and without ammonium nitrate application).