中文摘要：

以苏北沿海地区杨树林、杨农复合、草地和农田等4种不同土地利用方式为研究对象，采用原位封顶法测定了其土壤矿质氮含量及其季节动态。结果表明：土壤氮矿化速率季节变化显著，最大值出现在春季。不同土地利用方式土壤净矿化速率表现为杨树林〉杨农复合〉农田〉草地。不同土地利用方式土壤NH4＋-N、NO3--N含量均表现出显著的季节变化，土壤NH4＋-N、NO3--N含量最大值均出现在春季。土壤氮矿化随土层深度的增加而降低，土壤矿质氮含量随季节与土层深度变化。在10～25cm土层，杨树林土壤矿质氮含量与杨农复合之间差异显著（P〈0．05）；杨树林和草地土壤矿质氮含量在25—40cm土层与0～10、10～25cm土层之间差异显著（P〈0．05）。在春季表层土壤中，杨树林土壤矿质氮含量与农田、草地的差异较为显著，杨树林显著高于农田、草地（P〈0．05）。

英文摘要：

The variations of soil mineral N under four different land use types （ i. e. poplar plan- tation, crop-poplar integrated system, grassland, and cropland ） in a coastal area of northern Jiangsu were investigated by a close-top incubation method. The net N mineralization rate under each of the four land use types was higher in spring than in autumn, winter and summer. The net N mineralization rate decreased in order of poplar plantation, crop-poplar integrated system, cropland and grassland. Ammonium N and nitrate N showed obvious seasonal variations under the four land use types. The concentrations of ammonium N and nitrate N were generally higher in spring than in other three seasons. The soil mineral N decreased with increasing soil depth. In 10-25 cm soil layer, the soil mineral N concentration was significantly different between poplar plantation and crop-poplar integrated system. In poplar plantation and grassland, the soil mineral N concentration was significantly different between 25-40 and 0-10, 10-25 cm soil layers. The concentration of soil mineral N was significantly higher in poplar plantation than in cropland and grassland in 0-10 cm soil layer.