Effect of copper and phosphorus application on nutrition and dry matter yield of soybean (Glycine max L.)

An experiment was conducted with a loamy sand soil having ph 7.42, EC 0.16 dS m⁻¹, organic carbon 0.28 per cent, available P 18.6 kg ha⁻¹, and DTPA-extractable Cu 0.25 mg kg⁻¹ soil to study the efect of phosphorus (0, 25, 50, 100 and 200 mg P kg⁻¹ soil as Kh₂PO₄) and Cu (0, 2.5, 5.0, 10 and 20 mg Cu kg⁻¹ soil as copper sulphate) application on dry matter yield and nutrition of soybean. A quadratic response of DTPA extractable Cu in soil after harvest to relative dry matter yield indicated that 90 per cent of the maximum dry matter yield was observed at a level of 1.0 mg Cu kg⁻¹ soil. The dry matter yield registered a declining trend when DTPA-Cu in soil exceeded a level of 4 mg kg⁻¹ soil. Maximum dry matter yield of crop was produced at shoot phosphorus concentration of 0.3 per cent and it declined thereafter. A shoot Cu concentration of 7.0 µg g⁻¹, which is well below the threshold value of 20 µg g⁻¹ that may cause toxicity in plants, produced 90 per cent of the maximum yield.