Effects Of Dicyandiamide On Ammonia Volatilization And Eco-toxicology Of Soybean In Soils

Laboratory experiments were conducted to investigate the influence of different varieties of nitrification inhibitors, different concentrations of nitrification inhibitors and different temperature on soil pH changes, ammonia volatilization and ammonium variety, furthermore, the effects of dicyandiamide on the germination and seedlings growth of soybean were also discussed. The results are summarized as follows:Soil pH quickly increased in the initial stage and then decreased slowly in all treatments, and showed higher values in dicyandiamide (DCD) and thiourea (TU) treatments than in potassium thiosulfate (PT) and control (CK) treatments during the whole experiment. Ammonia volatilization intensity followed the changes of soil's pH. Ammonia volatilization contents were higher in nitrification inhibitors treatments than in CK, and showed the following tendency: DCD> TU> PT. The variety of soil ammonium content and soil pH have the similar trend. Transformation of ammonium to nitrate was prolonged about three days by adding nitrification inhibitors.As experimental temperature increased, the peak value of soil pH, ammonia volatilization and soil ammonium were also increased and appeared in advance when DCD applied with urea. The application of DCD increased soil pH peak and slowed th decline of soil pH value, and these effects were greater as DCD concentrations increased. The application of DCD also increased ammonia volatilization peak, prolonged the period of ammonia volatilization, enhanced ammonia volatilization content. All of these effects were more significantly obtained in treatments with higher concentrations of DCD, and more clear in garden soils of Jincheng in Shanxi Province. Ammonium existed in soils for a longer time when DCD used, and the ammonium peak raised when DCD concentration increased.DCD inhibited soybean germination, and the inhibition were stronger with higher concentrations of DCD. Following DCD concentration increased, the root length and weight of soybean increased first and then reduced, while the stem root and weight of soybean increased at all concentrations of DCD. In garden soils of Hunan Agricultural University, DCD promoted the synthesis of chlorophyll a and b in soybean seedlings. In garden soils of Jincheng in Shanxi Province, the synthesis of chlorophyll a and b in soybean seedlings stimulated first and then inhibited following DCD concentration increased. DCD in low concentrations promoted the seedling roots of soybean on Cu and Mn absorption in both soils and on Fe and Zn absorption in garden soils of Hunan Agricultural University, whereas Fe and Zn absorption were inhibited in garden soils of Jincheng in Shanxi Province. DCD in high concentrations restrained the seedling roots of soybean on these four elements adsorption in both soils. In garden soils of Hunan Agricultural University, DCD promoted the seedling stems of soybean on Cu and Mn absorption, and with respect to Fe and Zn absorption DCD promoted in the initial stage and then inhibited in the later stage. In garden soils of Jincheng in Shanxi Province, DCD inhibited the seedling stems of soybean on all four elements absorption. Among all treatments, the accumulation of these four trace elements were higher in seedling roots than in stems of soybean.The emission of NH3 in plastic greenhouse was more dramatically in treatments with urea than without urea, and compared with the urea treatments, DCD application significantly enhanced ammonia volatilization, and induced accumulation of NH3 in plastic greenhouse.