Priming effect of ammonium nitrogen fertilizer on soil nitrogen in typical soils of Loess Plateau

Typical soils collected from north to south on loess plateau were chosen to study the priming effect of ammonium nitrogen fertilizer on soil nitrogen by the Bremner incubation method. The results showed that the sequestration of clay to NH4+-N must be considered in order to get reliable results when measuring the priming effect of NH4+-N on soil nitrogen. The priming effects of NH4+-N on soil nitrogen in different soils were significantly different on 20 d and 60 d (P≤0.01 and 0.05), respectively. On 40 d, priming effect of different soil types was different, but not significant. NH4+-N had positive priming effect on soil nitrogen of Eum-Orthic Anthrosols and Los-Orthic Entisols, but negative effect on that of Ust-Sandiic Entisols, NH4+-N had no priming effect on soil nitrogen of Hap-Ustic Isohumisols on 20 d and 40 d, but had significant negative priming effect on 60 d. Generally speaking, on 20 d and 40 d NH4+-N had negative priming effect on farmland, positive effect on forest and bare land and positive effect on grassland soil, whereas no priming effect on 60 d. The influence of organic material on priming effect was not significant on 20 d (P=0.0872) and 40 d (P=0.1641), but significant on 60 d (P=0.0490). NH4+-N had positive priming effect when alfalfa was added on 40 d, and nopriming effect on 20 d and 60 d, negative piming effect existed when Stipa bungeana was added on 20 d, 40 d and 60 d, while it did not have any priming effect when no organic material was added on 20 d, 40 d, and 60 d.