SUBSTITUTION OF AMMONIUM AND POTASSIUM FOR ADDED CALCIUM IN REDUCTION OF AMMONIA LOSS FROM SURFACE-APPLIED UREA

Ammonia (NH3) volatilization loss from surface application of urea must be reduced if urea is to gain further acceptance for use in pastures and on other non- or low-tillage systems which do not permit soil incorporation. The method used to reduce NH3 loss should not increase costs of the N fertilizer significantly. Preferably, the material used should itself be a fertilizer nutrient. The nitrate salts of the monovalent cations NH+4, K+, and Na+ were tested as substitutes for chloride or nitrate salts of Ca2+ to depress NH3 losses when mixed with surface-applied urea. Ammonia losses were measured from soils with different cation exchange capacities (CEC) in the laboratory, with residual N quantified by growing sudangrass on the variously treated soils under greenhouse conditions. Laboratory and/or greenhouse data indicate that NH3 loss from surface-applied urea was most effectively reduced by Ca salts. Substitution of K, Na, and NH4 salts for Ca salts was increasingly effective as soil CEC increased. Monovalent salts were effective in reducing NH3 losses if the soil had exchangeable Ca2+ + Mg2+. In sand, however, monovalent salts did not reduce NH3 losses. The order of effectiveness on nonsandy soils was Na+ = K+ > NH+4 in reducing NH3 loss. Potassium as KNO3 or KCl can be used effectively to partially replace (Ca + Mg) nitrate or chloride salts with urea to reduce NH3 losses. Ammonium nitrate was ineffective in reducing NH3 losses except where high N application rates were used or where little or no soil CEC existed. The efficacy of NH4NO3 seemed to be due to its acidic nature more than displacement of exchangeable Ca2+ + Mg2+. © 1982 Soil Science Society of America.