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Li G.-L.,Northwest University, China | Pang X.-M.,Tianshui Soil and Water Conservation Experiment Station
Land Use Policy | Year: 2010

The purpose of this study was to assess the effect of grassland (GL) conversion to cropland (CL) and cropland conversion to forest (FL) and orchard (OL) on soil C and N distribution in dry aggregate size fractions in Nihegou catchment of the southern Loess Plateau, China. Four main land-use changes were analyzed in different agronomic management systems in 2006. The soil is wind-deposited loessial parent materials with a rather homogeneous silty clay loam texture classified as Calcic Cambosols. The GL was long-term over-used grassland. The CL was changed from GL after 33 years tillage with conventional tillage and fertilizer. The FL and OL originated from long-term CL after 23- and 7-year planted, respectively. Samples were taken at soil depths of 0-20 cm and 20-50 cm and were subjected to a physical fractionation process by way of aggregate size. Soil aggregate size fractions, total C and N contents and distributions were determined on all soil samples. Three dry aggregate fractions of very coarse (2.0-0.2 mm), coarse (0.2-0.05 mm) and fine (<0.05 mm) were obtained by shaking and sieving for 20 min. After 33 years of tillage, CL had 22% lower content of very coarse aggregates (2.0-0.2 mm) and 34% higher contents of fine aggregates (<0.05 mm) than GL. FL and OL soils had increased 9% and 10% contents of very coarse aggregates, and decreased 2% and 8% contents of fine aggregates compared to the CL. C and N losses in whole CL soils were 31% and 26% higher than those in GL. However, conversion of land uses from CL to FL (after 23 years) and OL (after 7 years) has increased C and N stocks by 76% and 40% in FL soils and by 66% and 63% in OL soils, respectively. This accessorial C and N stocks were higher in very coarse aggregate fractions (1.10 kg C m-2 and 0.13 kg N m-2 in FL soils, 1.43 kg C m-2 and 0.17 kg N m-2 in OL soils); moreover, the C and N stocks in fine aggregate fraction increased by 8% and 33% in FL soils and by 58% and 69% in OL soils, respectively. This results showed that C and N turnover and loss in aggregate fractions of this silty clay loam soils was very fast. Conversion of land uses from CL to FL and OL has obviously recovered the soil structure, and improved soil quality. © 2009 Elsevier Ltd. All rights reserved. Source

Li Y.,CAS Institute of Remote Sensing Applications | Li Y.,Chinese Academy of Sciences | Gong J.,CAS Institute of Remote Sensing Applications | Gong J.,Chinese Academy of Sciences | And 3 more authors.
International Journal of Remote Sensing | Year: 2013

The Loess Plateau suffers the most serious soil erosion in China. Sloping cultivated land is one of the most common land types in the region, and it leads to severe soil erosion. Analyses based on fine resolution satellite imagery can play a key role in the surveying of sloping farmland. In this article, a combination of remote-sensing (RS) and geographical information system (GIS) techniques under the hierarchical classification framework is used to investigate the sloping cultivated land in the Xi-He ecological engineering demonstration region of the Loess Plateau. This article synthetically adopts Système Pour l'Observation de la Terre 5 (SPOT-5) high-resolution images, Thematic Mapper (TM) multi-spectral images, and a terrain map at a scale of 1:10,000 to calculate the spectral, textural, and slope attributes of the sloping land type. A Bayesian classification method is employed to distinguish the crop and non-crop areas with a priori knowledge provided by local experts. The Gabor filter and the grey-level co-occurrence matrices (GLCM) method are used in combination under a man-machine interactive interpretation to extract the differences of texture trends and density distributions between sloping cultivated land and terraces, and a window-based method of texture analysis operations is adopted. A classification accuracy assessment by field survey shows that the total interpretation accuracy exceeds 80%. The sloping cultivated land in the research region covers an area of 233.06 km 2, and the sub-watersheds, such as the Yangliu watershed, need key management in the future. © 2013 Copyright Taylor and Francis Group, LLC. Source

Li Y.,CAS Institute of Remote Sensing | Li Y.,Chinese Academy of Sciences | Gong J.,CAS Institute of Remote Sensing | Gong J.,Chinese Academy of Sciences | And 3 more authors.
International Journal of Remote Sensing | Year: 2014

Ecological restoration measures have been undertaken in loess hilly and gully regions since the 1970s to prevent soil loss and to improve the ecological environment in those regions. Orchard construction was the main ecological measure undertaken in the Luo-Yu-Gou watershed, and in this article we propose a coupled maximum a posteriori decision rule and Markov random field (MAP-MRF) framework for orchard identification based on landform and landscape factors. Support vector machine (SVM) classification was first performed to obtain initial classification results for the years 2003 and 2008. A series of factors including landform factor, landscape factor, and the spatial-temporal neighbourhood factor are used to obtain land-cover change information including the change in orchard class. Finally, field experiments were carried out in the case study region of the Luo-Yu-Gou watershed, and based on the experimental results, it was found that the quantity error and the allocation error of the classification results for 2008 were 0.0441 and 0.1037, respectively. © 2014 © 2014 Taylor & Francis. Source

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