Wendy Vance

Soil Profile Description Soil profiles were described using a combination of codes and definitions from the Food and Agriculture Organisation and the Department of Agriculture and Food Western Australia (FAO-ISRIC 1990; Purdie 1999; FAO-CSIC 2002). These codes and descriptions were compiled into a booklet entitled ‘Dataset and Code Definitions for the Soil Survey of Cambodia’. A data sheet for recording soil profile information at each site was also produced. Soil profiles were classified using the Cambodian Agronomic Soil Classification (CASC) (White et al. 1997) and World Reference Base for Soil Resources (IUSS 2006). Soil Chemical Analysis Laboratory analysis was completed on all horizons for a selection of the soil profiles. These soil samples were analysed by CSBP laboratories in Western Australia. All soil samples were air-dried, ground and sieved (<2 mm particle diameter). The following tests were used (i) electrical conductivity and pH in 1:5 soil:water suspension and pH in 0.01M CaCl2 (Rayment and Higginson 1992, pp15-23); (ii) organic carbon concentrations, (Walkley and Black 1934); (iii) concentration of exchangeable cations, Gilman and Sumpter method (Rayment and Higginson 1992, pp 164-169); (iv) DPTA trace elements (copper, Cu; zinc, Zn; manganese, Mn; iron, Fe) (Rayment and Higginson 1992, pp 110-114); (v) nitrate and ammonium nitrogen (Searle 1984); (vi) available phosphorus and potassium, Colwell method (Rayment and Higginson 1992, p 64); (vii) extractable sulphur (Blair et al. 1991); (viii) boron (Rayment and Higginson 1992, pp 115-120). The soil chemical data can be found in Tables 1 to 3 at the end of this report. Data Collection and Reporting For each soil profile, location information was collected using a hand held GPS. This has enabled mapping of the data, and will enable users of the data in the field to return to soil profile locations. All soil profile data has been placed into an Access database currently maintained by the Soil and Water Group at CARDI. Other districts included in this study were Ou Reang Ov in the Province of Kampong Cham and Tram Kak in the Province of Takeo. Results of these surveys can be found in soil survey reports for each district. In addition the results of these soil surveys have been used to generate soil-land unit maps of each district (Hin et al. 2005a,b,c) and assist in the assessment of land capability for field crops in each district (Bell et al. 2005a,b).

The acceleration of crop diversification in Cambodia in lowlands and in uplands could be facilitated by a process for the assessment of land capability for non-rice crops. Maize, soybean, mung bean, sesame and peanut appear to be the crops of most interest initially for land capability assessment, together with cassava and sugar cane. Land capability was determined for maize, soybean, mung bean, sesame and peanut in Banan district, Battambang province. Limiting factors for crops were identified, and land qualities rated for the soil types identified previously in a soil survey of the district. The main Soil groups on Banan district are Toul Samroung, Kein Svay and Kompong Siem. The calcareous phase of Kompong Siem soils that occurs on the lower slopes of limestone hills has low capability for non-rice cropping with alkalinity and waterlogging being the most likely limiting factors. By contrast, the Kein Svay soil has high capability for non-rice crops especially on the high levee banks. Toul Samroung soil, where it occurs in slightly elevated land within the rice plains, has fair capability for non-rice crops, but it is not recommended for non-rice crops in the main wet season due to inundation risk.

Soil Profile Description Soil profiles were described using a combination of codes and definitions from the Food and Agriculture Organisation and the Department of Agriculture and Food Western Australia (FAO-ISRIC 1990; Purdie 1999; FAO-CSIC 2002). These codes and descriptions were compiled into a booklet entitled ‘Dataset and Code Definitions for the Soil Survey of Cambodia’. A data sheet for recording soil profile information at each site was also produced. Soil profiles were classified using the Cambodian Agronomic Soil Classification (CASC) (White et al. 1997) and World Reference Base for Soil Resources (IUSS 2006). Soil Chemical Analysis Laboratory analysis was completed on all horizons for a selection of the soil profiles. These soil samples were analysed by CSBP laboratories in Western Australia. All soil samples were air-dried, ground and sieved (<2 mm particle diameter). The following tests were used (i) electrical conductivity and pH in 1:5 soil:water suspension and pH in 0.01M CaCl2 (Rayment and Higginson 1992, pp15-23); (ii) organic carbon concentrations, (Walkley and Black 1934); (iii) concentration of exchangeable cations, Gilman and Sumpter method (Rayment and Higginson 1992, pp 164-169); (iv) DPTA trace elements (copper, Cu; zinc, Zn; manganese, Mn; iron, Fe) (Rayment and Higginson 1992, pp 110-114); (v) nitrate and ammonium nitrogen (Searle 1984); (vi) available phosphorus and potassium, Colwell method (Rayment and Higginson 1992, p 64); (vii) extractable sulphur (Blair et al. 1991); (viii) boron (Rayment and Higginson 1992, pp 115-120). The soil chemical data can be found in Tables 1 to 3 at the end of this report. Data Collection and Reporting For each soil profile, location information was collected using a hand held GPS. This has enabled mapping of the data, and will enable users of the data in the field to return to soil profile locations. All soil profile data has been placed into an Access database currently maintained by the Soil and Water Group at CARDI. Other districts included in this study were Ou Reang Ov in the Province of Kampong Cham and Banan in the Province of Battambang. Results of these surveys can be found in soil survey reports for each district. In addition the results of these soil surveys have been used to generate soil-land unit maps of each district (Hin et al. 2005a,b,c) and assist in the assessment of land capability for field crops in each district (Bell et al. 2005a,b).

From 2003 to 2005 soil surveys were completed in the Kingdom of Cambodia as part of a collaborative project between the Cambodian Agricultural Research and Development Institute (CARDI), Murdoch University and Department of Agriculture and Food Western Australia. The project was funded by the Australian Centre for International Agricultural Research. This report provides the results of soil profile descriptions and soil chemical analysis completed in the Districts of Ou Reang Ov and Chamkar Leu in the Province of Kampong Cham (Figure 1). The locations of soil profiles in this report have been georeferenced and are shown in Figure 2 overlaid on a Landsat mosaic image (collected from 1989 to 1994; Source for this dataset was the Global Land Cover Facility, http://www.landcover.org.).

The expansion of crop diversification in Cambodia in lowlands and in uplands could be facilitated by a process for the assessment of land capability for non-rice crops. Maize, soybean, mung bean, sesame and peanut appear to be the crops of most interest initially for land capability assessment, together with cassava and sugar cane. Land capability was determined for the above field crops in predominantly sandy terrain of Tram Kak district, Takeo province. Limiting factors for crops were identified, and land qualities rated for the soil types identified previously in a soil survey of the district. The main Soil groups on the siliceous uplands are Prey Khmer and Prateah Lang. The deep sandy Prey Khmer soils have fair capability for cropping with low soil water storage and Al toxicity being the most likely limiting factors. By contrast, the Prateah Lang soil has poor capability due to waterlogging and low soil water storage, and the Bakan soil was not recommended for non-rice crops due to waterlogging and inundation risk.

Land capability was determined for non-rice crops (maize, soybean, mung bean, sesame and peanut) for the main soil-landscape mapping units on basaltic terrain in Ou Reang Ov district, Kampong Cham province. Limiting factors were identified, and land qualities rated for the soil types identified previously in a soil survey of the district. The main Soil groups on the basaltic uplands are Labansiek, Ou Reang Ov and Kompong Siem. On the Labansiek soils, most of the land qualities were rated as favourable, and generally non-limiting. Overall land capability was rated as fair to good (Class 2-3), depending mostly on low soil pH and perhaps erosion risk. Overall land capability of the Ou Reang Ov Soil group was rated as fair (Class 3), depending mostly on low soil water storage and perhaps sub-soil pH, poor soil workability and crusting. The poor soil workability could be upgraded with the use of tractor drawn tillage rather than animal draft. Similarly the severity of limited soil water storage in the profile depends on seasonal rainfall and is likely to vary between the early and main wet seasons, and between years. Overall land capability on Kompong Siem soils was rated as good to fair (Class 2-3), depending mostly on waterlogging, which in turn can vary with growing season and among years. Despite a range of different limiting factors, the clayey soils which are commonly found in eastern Cambodia associated with basalt appear to have fair to good capability for cropping.

Opportunities for poverty alleviation in Cambodian agriculture are emerging in diversification from traditional wet season lowland rice (Oryza sativa) production to double-cropped, rice-based production systems and to upland cropping. The potential for double-cropping rice-based production will depend on understanding land capability for a range of non-rice crops in the lowlands of Cambodia. In addition, there are relatively large areas of land available for the expansion of upland cropping especially since the establishment of improved security and roads in rural Cambodia. The process of crop diversification in Cambodia could be facilitated by assessment ofland suitability for field crops in lowlands and in uplands. Land capability needs to be assessed for a range of field crops with realistic prospects for specific agro-ecosystems in Cambodia. Maize, soybean, mung bean, sesame and peanut appear to be the food crops of most interest initially, together with cassava and sugar cane. Usually soil constraints are assessed for land capability classification from published land resource studies. Such information is generally unavailable for uplands in Cambodia at an appropriate scale. Hence further land resource assessment in the upland areas is needed to undertake a more comprehensive land suitability assessment. Whilst a soil map for lowland rice has been published, soil constraints for non-rice crops have not been assessed for these soils. Land suitability is currently being determined for selected field crops that are relevant to landscapes in the study areas in Takeo, Kampong Cham and Battambang provinces. Toposequences in these provinces will be surveyed to characterise soils based on a variety of parent materials. In the lowlands, the focus will be on the identification of land suitability for double cropping (e.g. legume-rice, rice-legume) in rice-based systems. In the uplands, the focus will be on rainfed field crops that can be introduced into or expanded in Cambodia. The highest priority will be assigned to those crops that are already well established in Cambodia, including maize, soybean, and mung bean. Socio-economic input to land suitability assessment will be in the form of a GIS approach that will adjust land capability values spatially according to three key drivers of crop diversification: market access factors, population pressure, and poverty indicators.

Only the rice soils of Cambodia have been described in detail (White et al. 1997). The naming and identification of the Rice Soil groups has become familiar to agronomists, extension officers and farmers in Cambodia due to their common usage and the many training programmes conducted on their identification and properties (Heer et al. 1999). However, the Rice Soil Manual does not describe all the soils of Cambodia (White et al. 1997). The key for identification of rice soils allows for undefined and unclassified soils. Most of the non-rice soils of Cambodia are likely to fall into this category. Increased emphasis on crop diversification and upland farming has created a need for more detailed information on the soils in these upland areas. This is one of a series of Notes describing new Soil groups on upland soils that are proposed for inclusion into the Cambodian Agronomic Soil Classification (CASC). The Ou Reang Ov Soil group has been recognised and described by the CARDI Soil and Water Research program under ACIAR Project, “Assessing land suitability for crop diversification in Cambodia and Australia”. The purpose of this note is to assist agronomists, extension officers and farmers to recognise the Ou Reang Ov Soil group, to outline its main limiting factors, soil management requirements, and potential for land use.

Land capability needs to be assessed for a range of crops in specific agro-ecosystems of Cambodia to support moves to diversify crop production from the present heavy reliance on rice. Maize, soybean, mung bean, sesame and peanut appear to be the food crops of most interest initially. Usually soil constraints would be assessed for land capability classification from published land resource studies. Such information is generally unavailable for uplands in Cambodia at an appropriate scale. Hence further land resource assessment in the upland areas needs to be undertaken as a basis for a land capability assessment. Whilst a soil map and reports on soil constraints for lowland rice have been published, soil constraints for other crops have not yet been assessed for these soils. A framework for land capability classification was developed based on previous systems of land evaluation with modifications for Cambodia and to align the rating of land qualities to the Fertility Capability Classification. Land qualities were selected for tillage, crop germination and emergence, crop growth, and land and resource degradation risk. In subsequent papers, we report on the application of this classification to soils and landscapes of Kampong Cham, Takeo and Battambang provinces.

Only the Rice Soils of Cambodia have been described in detail (White et al. 1997). The naming and identification of the rice soil groups has become familiar to agronomists, extension officers and farmers in Cambodia due to their common usage and many training programmes conducted on their identification and properties (Heer et al. 1999). However, the Rice Soil Manual does not describe all the soils of Cambodia (White et al. 1997). The key for identification of rice soils allows for undefined and unclassified soils. Most of the upland soils of Cambodia are likely to fall into this category. Increased interest in crop diversification and upland farming has created a need for more detailed information on the soils in these areas. This is one of a series of Notes describing new soil groups or new phases of existing groups that are proposed for inclusion into the Cambodian Agronomic Soil Classification (CASC). A new phase of Kompong Siem Soil Group has been recognised and described by the CARDI Soil and Water Research program under the ACIAR Project, “Assessing land suitability for crop diversification in Cambodia and Australia”. The purpose of this note is to assist agronomists, extension officers and farmers to recognise a new calcareous phase of the Kompong Siem Soil group, to outline its main limiting factors, soil management requirements, and potential for land use.