Slow release sources of acetylene to inhibit nitrification in soil

Acetylene at partial pressures of 0.1 to 10 Pa blocks nitrification, but because it is a gas, it is difficult to apply and maintain at the required concentration in soil to inhibit the oxidation of ammonium. This problem may be overcome by coating calcium carbide with wax, or by forming a matrix with an insoluble material, to slow its reaction with water, and produce acetylene in situ in soil. This paper reports research which was conducted to develop and evaluate the effectiveness of polyethylene and polypropylene matrices, containing small particles of calcium carbide (1-200 mu m dia.) and various additives, to act as slow release sources of acetylene to inhibit nitrification in soil. The additives were used to provide microbridging in the matrix and hence controlled water penetration and acetylene generation and release. The matrices and wax coated calcium carbide (2 mm dia.), which has been used successfully for this purpose, were evaluated by following the oxidation of ammonium to nitrate in a fine textured grey clay. All matrices were at least as good as wax coated calcium carbide, at the same rates of active ingredient, as inhibitors of nitrification and some were considerably better. A matrix containing 21% calcium carbide proved to be a better inhibitor than the other materials. This matrix inhibited nitrification until day 90, and considerably slowed the oxidation to day 178. As wax coated calcium carbide has been shown to inhibit nitrification in fields of irrigated wheat, maize, cotton, and flooded rice, the results suggest that this matrix would be effective in preventing nitrification of fertilizer and soil nitrogen.