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

TLDR: It was found that chickpeas were less sensitive to the inhibitory effects of NO3− than soybeans, and there appeared to be a trend suggesting an inhibitory effect of 6 mMNO3− on C2H2 reduction compared to 1.5 and 3.0 mM NO3 −.

Abstract: 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 − .