Distribution of available soil water capacity in China

The available soil water capacity (ASWC) is important for studying crop production, agro-ecological zoning, irrigation planning, and land cover changes. Laboratory determined data of ASWC are often not available for most of soil profiles and the nationwide ASWC largely remains lacking in relevant soil data in China. This work was to estimate ASWC based on physical and chemical properties and analyze the spatial distribution of ASWC in China. The pedo-transfer functions (PTFs), derived from 220 survey data of ASWC, and the empirical data of ASWC based on soil texture were applied to quantify the ASWC. GIS technology was used to develop a spatial file of ASWC in China and the spatial distribution of ASWC was also analyzed. The results showed the value of ASWC ranges from 15 × 10-2 cm3·cm-3 to 22 × 10-2 cm3·cm-3 for most soil types, and few soil types are lower than 15 × 10-2 cm3·cm-3 or higher than 22 × 10-2 cm3·cm-3. The ASWC is different according to the complex soil types and their distribution. It is higher in the east than that in the west, and the values reduce from south to north except the northeastern part of China. The "high" values of ASWC appear in southeast, northeastern mountain regions and Northeast China Plain. The relatively "high" values of ASWC appear in Sichuan basin, Huang-Huai-Hai plain and the east of Inner Mongolia. The relatively "low" values are distributed in the west and the Loess Plateau of China. The "very low" value regions are the northern Tibetan Plateau and the desertified areas in northern China. In some regions, the ASWC changes according to the complex topography and different types of soils. Though there remains precision limitation, the spatial data of ASWC derived from this study are improved on current data files of soil water retention properties for Chinese soils. This study presents basic data and analysis methods for estimation and evaluation of ASWC in China.

Using a systems modeling approach to improve soil management and soil quality

Soils provide the structural support, water andnutrients for plants in nature and are considered to be thefoundation of agriculture production. Improving soilquality and soil health has been advocated as the goal ofsoil management toward sustainable agricultural intensifi-cation. There have been renewed efforts to define andquantify soil quality and soil health but establishing aconsensus on the key indicators remains difficult. It isargued that such difficulties are due to the former ways ofthinking in soil management which largely focus on soilproperties alone. A systems approach that treats soils as akey component of agricultural production systems ispromoted. It is argued that soil quality must be quantifiedin terms of crop productivity and impacts on ecosystemsservices that are also strongly driven by climate andmanagement interventions. A systems modeling approachcaptures the interactions among climate, soil, crops andmanagement, and their impacts on system performance,thus helping to quantify the value and quality of soils.Here, three examples are presented to demonstrate this. Inthis systems context, soil management must be an integralpart of systems management practices that also includemanaging the crops and cropping systems under specificclimatic conditions, with cognizance of future climatechange.