Internal Boron Requirement of Young Sunflower Plants: Proposed Diagnostic Criteria

Abstract

In a greenhouse study, a significant increase in sunflower (Helianthus annuus L., cv. Hysun 33) dry matter yield was observed with boron (B) application to a B-deficient (hot water-extractable, 0.23 mg B kg⁻¹) calcareous soil of Missa series (Typic Ustochrept). Six rates of B, ranging from 0 to 8 mg B kg⁻¹ soil, were applied as H₃BO₃ along with adequate basal fertilization of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn). Four plants of sunflower were grown in each pot; two were harvested after 4 weeks of germination and the other two after 8 weeks. Maximum crop biomass was produced with 1.0 mg B kg ⁻¹, and application of ≥2.0 mg B kg⁻¹ proved toxic, resulting in drastic yield suppressions. Critical B concentration range for deficiency diagnosis in 4‐week‐old sunflower whole shoots appears to be 46–63 mg B kg⁻¹. However, critical concentration in 8‐week‐old plants was much less (i.e., 36 mg B kg^−l), presumably due to a dilution effect. As plant's internal B requirement can vary, in fact manifold, depending on the species, plant part, and plant age, only a relevant criterion can help in diagnosing the deficiency effectively.

Keywords:

• Hot water‐extractable B
• Helianthus annuus
• plant analysis
• critical concentration
• deficiency diagnosis
• calcareous soil

Acknowledgments

We thank Mr. M. Jawad for assistance in word processing of the manuscript.