الملخص الإنجليزي
Lime (Citrus aurantifolia) is an economically valuable crop for farmers in the Sultanate of Oman. In recent years, its production has declined sharply. The causes of decline are varied. A nutritional survey was conducted for the purpose of investigating the decline of bearing lime trees in the Wilayah of Barka at the Batinah coast, in the Sultanate of Oman. Leaf (363) and soil (66) samples were analyzed for seven elements. In addition, soil pH, salinity, calcium carbonate content, and texture were determined.
Leaves of lime trees were sampled from 33 orchards. Samples were analyzed for N through the Kjeldahl method and for leaf P, K, Cu, Zn, Mn, and Fe through the dry ash method. Soil samples were analyzed for N using Kjeldahl and analyzed for P, K, Cu, Zn, Mn, and Fe using the AB-DTPA method. Data were analyzed using SPSS statistical software,
The leaf element contents results showed variable deficiencies, beginning with the most deficient: Zn >N> Mn>K>P> Cu > Fe. Elemental soil analysis showed deficiencies, beginning with the most deficient: N >Mn >P > Fe >K>Cu >Zn. Most elements were low in leaf samples, but Zn with 96.7 % of samples having a mean of 9.05 ppm and N with 81% of samples having a mean of 1.74% appeared to be the most deficient.
Soils were generally low in all elements, but N with 75.8% of samples having a mean of 0.055% seemed to be the most deficient element. Total Fe in leaf did not appear to reflect the actual Fe in lime tree when related to soil data. The deficiency of elements in trees were either due to low quantity in soil or low availability due to the effect of the high soil pH and the high CaCO3 content or because of some obscure relationship with the disease (Witches' Broom Disease of Lime). A fertilizer application strategy needs to be formulated to correct the nutrient deficiencies.
Elemental compositions of soil and leaf samples were correlated for the purpose of identifying important nutritional constraints to tree performance. Correlation analysis was performed to determine the significance of relationships between elemental leaf to soil, leaf to leaf, and soil properties to elemental leaf and soil concentrations.
Generally in leaves, concentrations of major nutrients were significantly correlated to minor elements. Leaf Fe was negatively correlated to leaf K and Zn, Soil N, Cu, and Zn were positively correlated to corresponding leaf elements. Most soil elements were interrelated except P. Soil pH was negatively correlated to leaf N and K. Soil calcium carbonate content was negatively correlated to leaf P. Soil texture was, in general, correlated to leaf P, Fe, Zn and Mn, Many major and minor elements in leaf samples appeared to be interrelated to each other, and also related to available nutrients in soil. In particular, the relationship between N and Zn in leaf and soil samples suggested that orchard management should be aimed at simultaneous correction of deficiencies of these two elements.
This study provides empirical evidence that nutritional deficiencies play a major role in the decline of lime groves in the Barka region. Whether these deficiencies are related to the Witches' Broom Disease problem is still an open question. However, it is necessary to correct the nutritional deficiencies to enable both the diseased and healthy trees to produce economical yields. Therefore initiation of a corrective study is recommended.
