Phosphorus requirement of wheat under chloride and sulphate dominated salinities

In a greenhouse study conducted on a Typic Torripsamment, wheat was grown up to maturity at three salinity levels (ECe 6, 8 and 10 dS m⁻¹), predominated by either chloride (Cl:SO₄=7:3) or sulphate (Cl:SO₄=3:7) salts. Each ECe treatment including a non-saline control (ECe 1.2 dS m⁻¹) was established at four levels of added P (0, 30, 60 and 90 mg P kg⁻¹ soil). At salinity level of 6 dS m⁻¹ wheat growth at the boot stage was reduced significantly under all P treatments, but grain yield was reduced only in the low P treatments (0 and 30 mg P kg⁻¹ soil). At comparable ECe levels, the external requirement of P was about 50% less under SO⁴ than under Cl-dominated salinity, as grain yield as well as P and S uptake at 60 mg P kg⁻¹ soil under SO⁴ and 90 mg P kg⁻¹ soil under Cl-salinity were equal. The external P requirement of wheat also increased with increase in the ECe of soil, as grain yield at 30 mg P kg⁻¹ soil at ECe 6 and 60 mg P kg⁻¹ soil at ECe 8 under Cl- and 30 mg P kg⁻¹ soil at ECe 8 and 60 mg P kg⁻¹ soil at ECe 10 dS m⁻¹ under SO⁴-salinity were comparable. The magnitude of the grain yield response to application of 90 mg P per kg soil relative to zero P increased from 1.8 times in non-saline to 5–7 times under SO⁴-salinity and 7–9 times under Cl-dominated salinity.