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District Swabi of Khyber Pakhtunkhwa province is well known for growing sweet oranges. Without inorganic fertilizer, the yield and quality of oranges have been declining over time. Keeping in mind the importance of micronutrients in citrus, survey of 20 sweet orange orchards in the area was planned. Composite soil (0-30 cm) and relevant leaf tissue (4th leaf from top) samples of non-fruiting branches (10-15 years) were collected during July-August, 2015. Majority of the soils were light, having sandy loam (60%) as a dominant texture with remaining as silt loam and loam. All the soils were non-saline (<2 dS m-1) and medium alkaline (7.5-8.3) in reaction with overall adequate (>1.29%) organic matter content. Majority of the samples were adequate in available B (95%), Cu (95%), Fe (65%), Mn (60%) and Zn (55%). In contrast to soil, leaf tissue analysis illustrated that all 100% samples (B, Cu, Mn and Zn) and 70% (Fe) were below the critical limit of each nutrient for citrus. The association between organic matter content and each B (0.53), Fe (0.67) and Zn (0.80) was linear and significant showing contribution of this pool in available nutrients. The regression coefficient (R2) explained a poor and non-significant relationship with only 26% (B), 3% (Cu), 21% (Fe), and 18% (Mn) contribution to leaf tissue nutrients from soil available pool. From this study it is inferred that orchards of district Swabi require application of B, Cu, Fe, Mn, and Zn, with emphasis to regular monitoring and soil testing for specific fertilizer recommendations.
Keywords: B; citrus; Cu; Fe; Leaf tissue; Mn; Zn