Improvement of Livestock Production in Crop-Animal Systems in ...

Appendix ICambodiaRainfed animal agriculture in nine countriesEnvironment and cropping systemsCambodia is bordered in the north by the Lao PDR and Thailand, in the west by Thailand, in the south by theGulf of Thailand and in the east by Vietnam. The total area of the country is estimated to be about 181,000 km 2 ,about 65% of which is forested. The climate is tropical monsoonal and is characterised by a wet season fromMay to November and a dry season from December to April, which has implications for the availability of feedresources. Most rice areas receive 1250–1750 mm of rainfall annually, but in some coastal areas rainfall may beas high as 4000 mm. Rainfall can vary widely from year to year. Dry season crops must rely entirely on irrigationor retained soil moisture. Relative humidity varies throughout the year from 60–80%. Temperatures are relativelyconstant, with mean monthly values ranging from 25°C in January to about 29°C in April.More than 50% of the rainfed lowland and upland rice crops are grown on soils of low potential. Thesoils are infertile because of continuous cropping and inadequate replacement of lost nutrients. Chemicalproperties vary appreciably, depending on soil type, and the majority of soils have poor internal drainage.The most common soils for the production of lowland rice are the ultisols and alfisols. Approximately 1.0million ha out of 1.87 million ha are ultisols and alfisols. The pH of ultisols ranges from 4.7–5.4, and thesoils contain high levels of aluminium. The pH of alfisols varies more widely from 4.8–9.4. Levels of availablenutrients such as nitrogen and phosphorus are low, and the capacity of the soils to hold and exchange cationsis limited. Physical constraints include poor structure, poor hydraulic properties and surface crusting.Extensive descriptions of Cambodian farming systems have been made by Delvert (1961) and Tichit(1981). Two main types of farming systems exist. One is rice-based and the other based on multiple cropping.Rice-based cropping systems predominate in Cambodia, and occupy 88% of the total cropped land (Nesbitt1996). Rubber and maize are the most important crops after rice. Other secondary crops grown includemungbean, tobacco, soyabean, cassava, sweet potato and sesame. Vegetable production is important alongthe Mekong River.Rice production systems can vary according to the flooding regime, planting season, level of watercontrol, planting pattern, topography and soil type. Five major rice systems exist in Cambodia, but onlyrainfed lowland and upland rice are relevant to this study. The former is planted from June to October andharvested from October to December; the latter is planted from April to June and harvested in December.Rainfed lowland rice is transplanted and grown on flat land where it is easy to construct bunds. Riceproduction is dominated by the lowland crop (85.7%) consisting mostly of medium- to late-maturing varieties.Some 92% of lowland rice is grown in the wet season as a single crop, with yields averaging 1.3 t/ha. Thearea cultivated per household varies from