贵州喀斯特山地农业系统不同种植区休耕地土壤水溶性氮素组成及分布特征

选择贵州喀斯特山地农业系统不同种植区休耕地土壤作为研究对象,对其水溶性氮素组成及分布特征进行了研究。结果表明:休耕地土壤SON含量范围为4. 11～14. 34 mg/kg,平均含量为8. 62 mg/kg。不同种植区休耕地土壤SON含量存在较大差异,但差异不显著(p0. 05),SON占TSN的比例差异极显著(p0. 01),传统农业种植区SON的变异较大,其它种植区的较小。水溶性氮素组成以SON和NH_4~+-N为主,不同种植区的NH_4~+-N、NO_3~--N占SIN的比例差异不显著(p0. 05),而两者占TSN及SIN占TSN的比例差异极显著(p0. 01)。传统农业种植区表层和深层土壤SIN的含量都要比其它种植区高,SON则相反,说明不同类型的农业对土壤氮的影响不同。不同种植区表层土NH_4~+-N、NO_3~--N、TSN、SON含量差异极显著(p0. 01)。除了打通种植区,其它种植区NH_4~+-N含量随着土层的增加总体上表现出下降的规律。除了大冲种植区在0～30 cm深度先增加后降低的规律外,其它种植区NO_3~--N含量自土壤表层到30 cm深度,随着土层的增加而增加,自30 cm深度往下,随着土层的增加而下降。TSN和SON中,除了青岩种植区随着土壤表层到20 cm深度处降低外,其它种植区随着土壤表层到20 cm深度处先增加,然后从20 cm深度往下随着土层的增加再降低。SON容易向下淋失,不易在土层深部发生积累,造成氮素的流失和带来环境污染风险,应引起重视。

Distribution and Composition of Water-soluble Nitrogen in Abandoned Cropland Soils from Different Cultivated Areas of Karst Mountain Agricultural System in Guizhou

The abandoned cropland soils in different cultivated areas of karst mountain agricultural system in Guizhou were selected as research object and its composition and distribution characteristics of water-soluble nitrogen were studied. The results showed that the content of SON ranged from 4.11 mg/kg to 14.34 mg/kg, with an average content of 8.62 mg/kg. No significant difference was found for SON contents of abandoned cropland soils in different cultivated areas(p>0.05), while significant difference for the ratios of SON to TSN(p<0.01). The variation of SON in traditional agricultural cultivated areas was larger than that in other areas. SON and NH₄⁺-N were the main form of water-soluble nitrogen in the abandoned cropland soils, the difference of ratio for NH₄⁺-N and NO₃^--N to SIN was not significant(p>0.05), but the ratio of NH₄⁺-N and NO₃^--N to TSN and SIN to TSN was significant(p<0.01), respectively. The content of SIN in surface and deep soil of traditional agricultural cultivated areas were both higher than that of other areas, but the content of SON was contrary, indicating that different types of agriculture have different effects on nitrogen in soil. There was a significant difference for NH₄⁺-N, NO₃^--N, TSN and SON content in surface soils among different cultivated areas(p<0.01). A downward trend with the increase of soil layer for the content of NH₄⁺-N was found in these cultivated areas except for Datong area. The content of NO₃^--N increased with the increase of soil depth from surface to 30 cm, and decreased with the increase of soil depth from 30cm to deeper layer in these cultivated areas but first increased and then decreased with the increase of soil depth from surface to 30 cm in Dachong area. For TSN and SON, showed that their contents first increased with the depth of soil surface to 20 cm, and then decreased with the increase of soil depth from 20 cm to deeper layer in these cultivated areas but decreased with the increase of soil depth from surface to 20cm in Qingyan area. indicating that SON is easy to leach downward and not easy to accumulate in the deep layer of soil, causing nitrogen loss and increasing environmental pollution risk, which should be concerned.