An assessment of non-symbiotic nitrogen fixation in some Nigerian soils by the acetylene reduction technique

Short-term incubation studies of non-symbiotic nitrogen fixation using acetylene as the substrate for nitrogenase were carried out on six soil samples collected from various locations in the Western State of Nigeria, and on one soil sample collected from Wisconsin, U.S.A. Unamended soils reduced a very small amount of acetylene but with added organic materials (5% organic matter, 2% glucose or sucrose) acetylene reduction became substantial and in one case was more than 30,000 times that in the unamended soil. In general, more acetylene was reduced in anaerobic than in aerobic soils. Two of the soils were tested for suppression of acetylene reduction by NH₄⁺-N. With the addition of up to 100 ppm nitrogen as (NH₄)₂SO₄ to the soils incubated with sucrose, no depression of acetylene reduction was observed in one soil while it was reduced by about half in the other.