Mineralization of guanidine derivatives in soils

Abstract

Mineralization of eleven guanidine derivatives was studied in three soils of varying levels of microbial biomass C to evaluate their potential as fertilizer N sources. The guanidines mineralized slowly. Their mineralization generally started after a lag phase which increased with concentration. Mineralization of dimethylguanidine sulphate was the fastest (7–63 days) and tetramethyl guanidine slowest (>98 days) in all soils and at concentrations equivalent to 100 and 500 μg N g-1 soil. The mineralization rates increased with concentration except for guanidine hydrochloride, guanidine thiocyanate, nitroguanidine, and tetramethyl guanidine. They mineralized faster in soils with higher microbial biomass C. The mineralization of guanidines may be classified into four groups: rapidly mineralized (dimethyl guanidine sulphate); mineralized after a lag phase (guanidine sulphate, guanidine carbonate, guanidine acetate, guanidine hydrochloride and guanidine thiocyanate); a fraction of applied N rapidly mineralized with the gradual mineralization of the remaining N (guanidine nitrate, aminoguanidine nitrate, aminoguanidine carbonate); and very slowly mineralized (nitroguanidine, tetramethyl guanidine). None of the guanidines inhibited germination of wheat and excepting guanidine hydrochloride which reduced growth or guanidine thiocyanate that killed seedling, other guanidines increased the dry matter production.