紫色土坡耕地硝酸盐淋失特征

Characteristics of nitrate leaching from hilly cropland of purple soil

利用具有壤中流测定功能的径流小区的定位观测结合土壤剖面硝酸盐累积的动态分析,研究了紫色土坡地硝酸盐淋失特征.结果表明,紫色土坡地硝酸盐呈旱季累积,雨季淋失的特点,而壤中流是紫色土硝酸盐淋失的主要通道.紫色土为土层浅、土壤下伏透水性极弱的紫色泥页岩,同时夏季降雨丰富,壤中流极为发育,2003～2005年壤中流平均流量为169.7mm,占雨季径流量的52.42%,其中,NO3--N含量持续偏高,2003～2005年平均含量高达14.92mg.L-1.3年平均随壤中流淋失的硝态氮达27.98kg.hm-2,占年施肥量的10.0%,硝酸盐淋失具有季节与年际间差异,淋失负荷主要受壤中流流量影响.紫色土坡地硝酸盐随壤中流大量淋失不仅造成当地浅层地下水硝酸盐污染,而且将加剧长江三峡库区水环境压力.

Nitrate leaching from hilly cropland of purple soil was studied by monitoring and analyses of nitrate accumulation in soil profiles. Experiments were conducted from 2003 to 2005 in artificial small catchments with subsurface flow monitoring. Results showed that nitrate accumulated in dry seasons and diminished in rainy seasons on the hilly cropland. Subsurface flow is the main pathway of nitrate leaching in the rainy season. Nitrate leaching through subsurface flow was influenced by a shallow soil layer （60 cm） , low infiltration parent rock beneath the soil, and heavy rainfall in summer. Average annual discharge of subsurface flow from 2003 to 2005 was 169.7 mm, which amounted to 52.42% of total runoff in the rainy season. The content of NO3^- -N in subsurface flow was persistently high with an average of 14.92 mg·L^ - 1 between 2003 and 2005. Annual average loss of NO3^- -N through subsurface flow was 27.98 kg·hm^ - 2, and accounted for 10.0% of total fertilizer nitrogen applied within a year. NO3^- -N loss rates through subsurface flow showed seasonal patterns. It peaked during maize elongation and stamen stages, which accounted for 69% of the annual NO3^- -N loss flux. Nitrate loss through subsurface flow results in in situ groundwater pollution and downstream pollution. Pollution by long-distance travel of soluble nitrate could become a major threat to the water quality in the region of the Three Gorges Reservoir.