The effect of soil nitrate on the growth, nodulation and nitrogen fixation of chickpeas (Cicer arietinum)

Summary

A controlled environment experiment was used to examine the growth and nodulation response of chickpea to a range of soil nitrate (NO ⁻₃ ) levels (0, 0.75, 1.5, 3.0, 6.0 mM). Dry matter production, nodule mass and number, dinitrogen (N₂) fixation via the acetylene (C₂H₂) reduction method, total nitrogen content and NO ⁻₃ concentration were measured at 56 and 90 days from inoculated and uninoculated plants. It was found that chickpeas were less sensitive to the inhibitory effects of NO ⁻₃ than soybeans. High NO ⁻₃ appeared to inhibit the production of nodules early in growth, however, by the second harvest nodulation was stimulated by high NO ⁻₃ levels. Increasing NO ⁻₃ levels gave positive responses in tops and roots dry weight production but, proportionally, these effects were greatest with uninoculated plants. 3 and 6 mM NO ⁻₃ gave similar root and tops dry weight in inoculated plants after 90 days. Nodule dry weight production per pot was maximised at 3.0 mM NO ⁻₃ at both plant harvests. Whilst NO ⁻₃ at 6 mM still gave a strong stimulation of acetylene reduction compared to 0 and 0.75 mM NO ⁻₃ , there appeared to be a trend suggesting an inhibitory effect of 6 mM NO ⁻₃ on C₂H₂ reduction compared to 1.5 and 3.0 mM NO ⁻₃ .