Spatial Distribution of Nitrate in Vineyards Soils in Yongding River Basin, Hebei Province

The relationship between nitrogen input, elevation of vineyards and soil nitrate content and accumulation in Yongding River Basin was studied, in order to provide a theoretical basis for rational fertilization and reduction of environmental pollution risks of vineyards in Yongding River Basin.

52 typical vineyards in Yongding River Basin of Hebei Province were selected as the research objects. The current situation of nutrient input in the vineyard was analyzed through field investigation. Soil nitrate contents of 0-60 cm (20 cm interval) was measured through indoor analysis, and its accumulation and surplus were calculated. Spatial variability of nitrogen input and surplus, soil nitrate content and accumulation were analyzed by ArcGIS geostatistics.

Less than 50% of farmers in Yongding River basin applied organic fertilizer, mainly using inorganic fertilizer. The average nitrogen input in upstream and downstream vineyards was (1 492.79±988.90) and (1 079.31±638.25) kg·hm^-2, respectively. The average nitrogen surplus were (1 430.41±993.01) and (1 027.23±637.37) kg·hm^-2, respectively. There was a significant positive correlation between nitrogen input and surplus (P<0.01), and the spatial distribution showed a decreasing trend from west to east. The variation and spatial distribution of soil nitrate content and accumulation in different soil layers were consistent. The low value area was mainly distributed in the downstream, while the high value area was mainly distributed in the upstream. The average nitrate content of 0-60 cm soil profile in the upper and lower reaches was 34.96 and 18.76 mg·kg^-1, respectively, and the average cumulative amount was 92.44 and 48.12 kg·hm^-2, respectively, which showed significant differences among different soil layers. Soil nitrate content and accumulation in the upper reaches were the lowest in the 20-40 cm soil layer, and increased with the increase of soil layer in the lower reaches. Soil nitrate content and accumulation in the upper reaches were the highest at 600-650 m elevation, which were significantly higher than those at other elevations (P<0.05). However, soil nitrate content and accumulation in the lower reaches were not significantly affected by elevation. Correlation analysis showed that the distribution of nitrate accumulation in the surface layer were mainly affected by elevation, while in the bottom layer were mainly affected by nitrogen input.

In the Yongding River Basin, the nitrogen surplus of vineyards in the study area was serious, and the nitrate in the vertical soil layer accumulated to the deep layer. The soil nitrate content and accumulation at different elevations (except 450-500 m) were higher in the upstream than in the downstream, but the variation trend of vertical distribution was different, which was jointly affected by the elevation and nitrogen input.