Effects of Boron Fertilization on Sunflower Grown on Low Boron Sandy Soil

Agronomists evaluate soil boron fertility with the threshold of around 0.5 mg kg^-1(hot water extraction). The nonappearance of boron deficiency on sunflower, when grown on low boron sandy soil, was investigated to test the validity of this boron guideline fertility. The soil boron content was around 0.19mg kg^-1. Pot experiments were conducted during 2015 season and repeated during 2016 season. Six boron levels were applied to soil: (0, 0.2, 0.5, 1, 5, and 10mg kg^-1) in 2015 and (0, 2, 5, 10, 15, and 20mg kg^-1) in 2016. Boron was applied as Solubor-C (Na₂B₈O₁₃.4H₂O, 21% of boron). The results revealed that soil boron application did not enhance kernels weight and kernels oil and protein contents. However, boronsupplyhigher than or equal to 1mg kg^-1 resulted in visible leaf damage. Also, a significant decrease in kernels weight was recorded at high boron levels (15 and 20 mg kg^-1). The kernels boron content did not increase with a successive increase in dose of boron supply. It was sufficient, around 16mg kg^-1, for all boron tested amounts. Also, plant content on other nutrients was not affected by boron application. The soil residual boron enrichment was around 0.3 mg kg^-1 for each boron application of 2 mg kg^-1.