Response of Pigeonpea to Applied Zinc in Ustifluvent Soils of Western Uttar Pradesh

Pigeonpea (Cajanus cajan L. Millsp.) when raised in pot-culture on an adequately fertilized loamy sand. Gangetic upland semi-arid alluvial soil (Ustifluvent) of Putti village, Bulandshahar district in western Uttar Pradesh showed positive responses to graded (1 to 25 mg kg⁻¹ soil) Zn amendment. The increase in height, branching, production of pods and harvest index of pigeonpea was highest at 5 mg kg⁻¹ Zn added soil which raised DTPA extractable soil Zn from 0.41 to 1.23 mg kg⁻¹. The optimal growth of pigeonpea was at 1.23 mg kg⁻¹ available soil Zn and in middle leaves the concentration of Zn was 42.2 mg kg⁻¹ (d 67). Critical values helpful in predicting 50 per cent crop responses to Zn amendment were 0.52 mg kg⁻¹ DTPA soil Zn and 25 mg Zn kg⁻¹ in middle leaves, 0.90 mg kg⁻¹ DTPA-Zn and 16.8 mg kg⁻¹ leaf Zn for top yield. The threshold of deficiency values were 0.70 mg kg⁻¹ for DTPA soil Zn and 23.6 mg kg⁻¹ for leaf Zn. DTPA soil Zn valnes of 5.8 mg kg⁻¹ and tissue Zn 43.4 mg kg⁻¹ in middle leaves indicated marked toxicity of Zn for top yield. The corresponding values representing threshold of toxicity were 3.0 mg kg⁻¹ DTPA extractable Zn and 36.8 mg kg⁻¹ Zn in middle leaves. These values will be helpful in predicting Zn status of soils as well as for crop plants growing on them.