4.2. Spatial pattern difference at vertical direction
Conversion of natural land into farmland affects soil properties, especially the surface layer (De Alba et al., 2004). The spatial relationships of the eight soil parameters in the two layers are different as a consequence of the land use conversion. The four scenarios analysis of two land uses indicate that the eight soil properties are not the dominant factor affecting the diffuse N pollution. The findings show that diffuse N loading is complex under different land uses. In this agricultural area, the two types of farmlands both originated from wetlands. Their vertical differ- ences of correlation with soil properties mean that the tillage practice in the surface changes the soil property and also intensify the diffuse N loading. The mineral fertilizer load in the top soil layer is the dominant factor and can be assessed by TN in rice paddies. The field investigations show that the heavy metal contents are controlled by the tillage practices, an outcome that has been reported by others (Camelo et al., 1997). Furthermore, the hydrological differences of the soil at the two depths also affect the N transport, and this is recognized in the SWAT uncertainty analysis (Bossa et al., 2012).
4.2. Spatial pattern difference at vertical direction Conversion of natural land into farmland affects soil properties, especially the surface layer (De Alba et al., 2004). The spatial relationships of the eight soil parameters in the two layers are different as a consequence of the land use conversion. The four scenarios analysis of two land uses indicate that the eight soil properties are not the dominant factor affecting the diffuse N pollution. The findings show that diffuse N loading is complex under different land uses. In this agricultural area, the two types of farmlands both originated from wetlands. Their vertical differ- ences of correlation with soil properties mean that the tillage practice in the surface changes the soil property and also intensify the diffuse N loading. The mineral fertilizer load in the top soil layer is the dominant factor and can be assessed by TN in rice paddies. The field investigations show that the heavy metal contents are controlled by the tillage practices, an outcome that has been reported by others (Camelo et al., 1997). Furthermore, the hydrological differences of the soil at the two depths also affect the N transport, and this is recognized in the SWAT uncertainty analysis (Bossa et al., 2012).
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