Plant Yield and Nitrogen Content of a Digitgrass in Response to Azospirillum Inoculation

Abstract

Two Australian soils, a vertisol (pH 6.8, 0.299% N) and a sandy yellow podzol (pH 6.2, 0.042% N), were used with digitgrass, Digitaria sp. X46-2 (PI 421785), in a growth room experiment. Comparisons were made between plants inoculated with live and autoclaved bacterial suspensions of Australian and Brazilian isolates of Azospirillum brasilense . Seedlings were inoculated on days 10 and 35. Acetylene-reducing activity was measured five times during the experiment. Dry matter yields of the digitgrass on the podzol (low N) inoculated with live bacteria were 23% higher than those of the controls. On the vertisol (high N), yield increases from inoculation with live bacteria were 8.5%. The higher-yielding plants had significantly lower percent nitrogen, but when total nitrogen of the tops was calculated, the inoculated plants had a higher total N than did the controls ( P =0.04). Acetylene-reducing activity was variable in the experiment, ranging from 0.5 to 11.9 μmol of C 2 H 4 core −1 day −1 . Live bacterial treatment induced a proliferation of roots, possible earlier maturity, higher percent dry matter, and a higher total N in the tops.