Slow release sources of acetylene to inhibit nitrification in soil

Acetylene at partial pressures of 0.1 to 10 Pa blocks nitrification, but be cause it is a gas, it is difficult to apply and maintain at the required co ncentration in soil to inhibit the oxidation of ammonium. This problem may be overcome by coating calcium carbide with wax, or by forming a matrix wit h an insoluble material, to slow its reaction with water, and produce acety lene in situ in soil. This paper reports research which was conducted to de velop and evaluate the effectiveness of polyethylene and polypropylene matr ices, containing small particles of calcium carbide (1-200 mu m dia.) and v arious additives, to act as slow release sources of acetylene to inhibit ni trification in soil. The additives were used to provide microbridging in th e matrix and hence controlled water penetration and acetylene generation an d release. The matrices and wax coated calcium carbide (2 mm dia.), which h as been used successfully for this purpose, were evaluated by following the oxidation of ammonium to nitrate in a fine textured grey clay. All matrice s were at least as good as wax coated calcium carbide, at the same rates of active ingredient, as inhibitors of nitrification and some were considerab ly better. A matrix containing 21% calcium carbide proved to be a better in hibitor than the other materials. This matrix inhibited nitrification until day 90, and considerably slowed the oxidation to day 178. As wax coated ca lcium carbide has been shown to inhibit nitrification in fields of irrigate d wheat, maize, cotton, and flooded rice, the results suggest that this mat rix would be effective in preventing nitrification of fertilizer and soil n itrogen.