Measurements of Nitrate Leaching from a Hillslope Cropland in the Central Sichuan Basin, China

Abstract

Nitrate losses through leaching were studied in a crop field in the central Sichuan Basin, southwestern China, during 2003 to 2006. Nitrate accumulations and losses via leaching were measured using two methods: a simulation with sampled soil profiles and field monitoring in situ at a 7% slope. The results showed that NO3 was accumulated in the dry season and leached in the rainy season. No spatial dependence of soil NO3 distribution could be distinguished along the hillslope due to complex water flow. The soil interflow was the major driver of NO3 leaching losses from the experimental plots. The average annual discharge of the interflows was 148 mm, accounting for 63% of total runoff in the rainy season in 2003 to 2006. The interflow water contained high NO3–N concentrations. The highest NO3–N concentration and loss flux were detected in storm runoff after a long drought in 2006. The NO3–N leaching through interflow showed clear annual and seasonal patterns, and largely occurred in the stages from stamen elongation to maturity of maize (Zea mays L.) with a flux of 2.2 g m−2, about 69% of the total annual loss flux. Annual estimated losses of NO3–N through interflow ranged from 20 to 53, with an average of 36 kg ha−1 yr−1 This study indicates that croplands on hillslopes with regosols are vulnerable to NO3 leaching. The interflow discharge monitoring method together with effluent NO3 content analysis used in this study proved to be useful and effective for quantifying NO3 leaching losses at the field scale in hillslope areas.

Leaching is the dominant route for soil organic carbon lateral transport under crop straw addition on sloping croplands

“…The specific soil used is a silty loam soil with a pH of 8.3, bulk density of 1.3 g/cm 3 , organic carbon content of 5.1 g/kg, total nitrogen content of 0.6 g/kg, total phosphorus content of 0.6 g/kg, field capacity of 27.3%, and saturated hydraulic conductivity of 16.8 mm/h (Zhu et al 2009). …”

“…The experimental lysimeter plots (size: 8 × 4 m 2 , slope: 7%), allowed for the simultaneous measurement of surface runoff, leaching, and soil erosion. These free-draining lysimeters were placed by excavating the soil to the bedrock and constructed the lysimeters for hydrological isolation in 2002 (Zhu et al 2009). Each plot was hydrologically isolated by walls filled with cement that reached the bedrock and extended to a depth of at least 0.6 m to prevent lateral seepage from adjacent plots according to Patent No.…”

“…Regosols, which are characterized by thin soil layers, are easily saturated during precipitation. Leaching is a major phenomenon that occurs primarily during the rainy season (Zhu et al 2009). Hence, surface runoff, leaching, and soil erosion occur simultaneously on hillslope croplands during the rainy season.…”

Effect of long-term fertilization on soil aggregate-associated dissolved organic nitrogen on sloping cropland of purple soil

“…The experiment site is located in the Yanting Agro-Ecological Station of Purple Soil (31°16'N, 105°28'E) at an altitude of 400-600 m in the central Sichuan Basin, Southwest China. The experimental site has a moderate subtropical monsoon climate with an annual mean temperature of 17.3°C and mean precipitation of 826 mm over the past twenty years (Zhu et al 2009). There are 5.9, 65.5, 19.7 and 8.9% rainfall occurred in spring, summer, autumn and winter, respectively, during the total annual precipitation.…”

Modeling nitrogen loading in a small watershed in southwest China using a DNDC model with hydrological enhancements

“…The dominant soil in the watershed is classified as Pup-Orthic Entisol in the Chinese Soil Taxonomy or Entisol in the US Soil Taxonomy and is distributed along the hill slopes (B. Zhu et al, 2009). Because of its purple color, the soil is locally called purple soil.…”