黄土高原丘陵沟壑区植被恢复过程对土壤剖面矿质氮累积影响——以纸坊沟流域试验区为例

Influence of Vegetation Restoration Process on Mineral Nitrogen Accumulation in Soil Profile in Hilly and Gully Region of Loess Plateau ——Sample with Zhifanggou watershed experimental area

根据不同植被类型和不同植被恢复年限,在位于半干旱黄土高原丘陵沟壑区延安安塞纸坊沟流域采集68个剖面样品,探讨植被恢复过程土壤剖面中残留矿质态氮的变化;同时采取该流域连续14年施用不同肥料处理的坡地长期定位试验剖面土样,研究连续施肥对农田土壤剖面残留NO3--N累积的影响。结果表明,NH4+-N在土壤剖面中的分布和累积基本不受植被恢复及植类型的影响,但NO3--N在土壤剖面中的累积量随植被恢复而下降。林地、草地和农田0～50cm土层平均累积的NO3--N分别为17 4kg/hm2,14 9kg/hm2和39 9kg/hm2;林地和草地剖面中NO3--N累积量所占矿质氮总累积量比例远小于NH4+-N,而对农田土壤,剖面中NO3--N累积量所占比例与NH4+-N所占比例基本相当;农田土壤剖面中NO3--N累积量所占比例显著大于林地和草地。长期定位试验结果进一步证明了在农田连续施用氮肥会显著增加土壤剖面中残留NO3--N累积,当农田退耕还林还草后,累积的这一部分NO3--N因植物吸收利用、土壤生物固定和损失等途径而下降,最终达到低而稳定的水平。

According to different type of vegetation and their restored years, 68 soil profile sample were collected from Zhifanggou watershed in Ansai county located in hilly and gully region of the Loess Plateau to discuss the change of residual mineral nitrogen in soil profile; At the same time, soil samples collected from a long-term experiment situated the slope land in this area for 14 years were to study the effects of different fertilization treatments on the residual mineral nitrogen in profiles. The result indicated that the distribution and accumulation of ammonium nitrogen in soil profile were not influence by vegetation restoration, but nitrate nitrogen decreased in vegetation process. As for average nitrate accumulated in 0～50 cm soil layer was 14.4 kg/hm^2, 14.9 kg/hm^2 and 39.9 kg/hm^2 in forestland, grassland, farmland respectively. The ratio of nitrate nitrogen accumulation to total mineral nitrogen in forestland and grassland were obvious lower than ammonium nitrogen. However, it was basic same for the ratio of nitrate nitrogen accumulation to total mineral nitrogen and ammonium nitrogen accumulation to total mineral nitrogen in farmland. The ratio of nitrate nitrogen accumulation to total mineral nitrogen in forestland was higher than it was in forestland and grassland significantly.The results of long-time experiment further proved that this could cause a significant accumulation of nitrate nitrogen in soil profile by employing continuously with nitrogen fertilization in farmland. This part of nitrate nitrogen will decrease when farmland return to be forestland or grassland by plant absorption, microbial fixation in soil and loss, at last it will be in a low and steady level.