Cambodia’s climate is determined by the tropical monsoon which triggers the annual flooding of the Mekong / Tonle Sap Basin. The wet season is pronounced, lasting from May to October and the dry season from November to April. The wet season accounts for 80% of the annual rain, which averages between 1000mm to 2500mm, tending to fall irregularly and thus resulting in dry periods even within the wet season. In the central area, covering the Tonle Sap and lower Mekong valley, rainfall averages between 1200mm and 1900mm annually. Hydrological data exists only for Stung Treng, Kratie and Phnom Penh as their rainfall stations are still functioning. No comparisions are possible from data collected in the 1960s, as gauging stations are now in different places. In Siem Reap, the FAO is starting to collect hydrological data from scratch.
There is little spatial variation in temperatures, with a minimum average monthly temperature of 25 C in January and a maximum of 29 C in April. Relative humidity ranges from 65 to 70% in January / February, to 85-90% in August / September. Annual evaporation is in the order of 2000 to 2200mm, being highest in April / March and lowest in September / October.
The Department of Statistics, Ministry of Planning estimated Cambodia’s population at 9.3 million with a population growth of 2.8% in 1993. Other sources estimate the growth rate to be as high as 3.2% (Dennis and Woodsworth,1992). Although population density is low by Asian standards, averaging 52 persons per km, it is spatially highly variable with the central and southern plains experiencing densities ranging between 97 and 173 persons per km2 2 (UNDP 1994), whilst the north and northeastern provinces have densities of 1-5 persons per km2 (See Figure 1). This places Cambodia favourably with abundant natural resources and low population pressure, however this position is being rapidly eroded by high growth rates. A comprehensive national family planning campaign is needed if Cambodia is to achieve food self-sufficiency.
The burden of resource degradation is being particularly felt by women, who in 1990 made up 56% of the adult population with an estimated 35% of rural households headed by women, and 65-70% of the rural workforce being women. It is women who have the primary responsibility for meeting basic needs (collecting water and fuelwood) and thus they who are more dependent upon the natural resource base.
The agricultural sector provides the backbone of the Cambodian economy contributing half of the country’s GDP and employing 80-85% of the labour force in agriculture and its related sub-sectors (fisheries and forestry). The total cultivated area covers 21-22% of the country, with approximately two thirds, or about 2 million hectares of total arable lands flooding annually. It is on these flood plains surrounding the Tonle Sap, Mekong and Bassac rivers that 85% of rice production is grown under a lowland rainfed rice regime, tying the rice system to both the hydrological cycle of inundation and recession of the Mekong / Tonle Sap system and to fisheries. Rice production is dependent on the silt laden flood waters of the Mekong for its fertilizing effect, as are the life cycles of fish in the lower Mekong for their spawning and migration. To reflect the traditional practices of Khmer farmers, agriculture and fisheries must be developed simultaneously as an integrated system.
There are two main types of farming systems: rice based farming systems and multi-cropping systems. Rice based farming systems are estimated to cover 1.9 million hectares, (90% of the currently cropped area) and can be differentiated according to flood regime, planting season, level of water control and the planting pattern. The UNDP have divided rice cropping patterns in Cambodia into five categories, providing average yields for each type as well as developmental potential:
1- Rainfed lowland rice production covering 85% of cultivated area with an average yield of 1.3 tonnes per hectare. Rainfed rice is concentrated on the flat plains surrounding the Tonle Sap, Mekong and Bassac rivers. In the absence of improved water control, the scope for improving this system is limited.
2- Dry Season Flood recession rice covering 8% of cultivated area with an average yield of 2.7 tonnes per hectare. Flood recession rice is mainly grown in Takeo, Prey Veng and Kandal, benefitting from the annual siltation of the Mekong. This cropping pattern presents the highest potential in terms of productivity improvements.
3- Dry Season lowland irrigated rice covering less than 1% of the cultivated area, with an average yield of 1.4 tonnes per hectare. Cropping patterns are similar to flood recession patterns but have lower yields because of poorer soil.
4- Upland rice mainly in slash and burn systems covering less than 1% of cultivated area with an average yield of 1 tonne per hectare.
5- Floating rice covering 6% of the cultivated area with an average yield of 1.2 tonnes per hectare. Floating rice is grown in the delta around the Tonle Sap Lake. This system is subject to high risk of crop loss. Cultivation is extensive and normally provids relatively high returns to labour.
Subsidary food crops and cash crops produced in the country are, by order of importance: cassava, sugar cane, corn, sweet potato, soya bean, mung bean, tobacco, sesame, peanut, jute and black pepper.
The irregular and localized nature of rainfall is identified by IRRI (1993) (quoted in UNDP 1994) as one of the most serious constraints to the intensification of rainfed lowland rice production. Although rainfall is usually of sufficient quantity, it is irregular in its distribution; the excess of water in one period does not compensate for the deficiency of another. The rainy season can be characterized according to three periods which contribute to problems in rice culture:
1- The late arrival of April rains combined with the difficulty of insufficient rains in May/June which often delay land preparation.
2- The small dry season in July/August when rainfall ceases or is irregularly distributed and usually insufficient for optimum growth of rice plants.
3- Heavy rainfall during September and October which can cause extended periods of rice innundation and flooding. The rains are acidic which can contribute to the lowering of soil pH and leaching of the soils. The early cessation of rainfall in November can have an adverse effect during the principal rice flowering dates.
There is a lack of improved local rice plant varieties adapted to Cambodia’s wet season, different agroecological environments, cultural conditions and acceptable to farmers. In general, farmers must rely on low-yielding, strongly photoperiod sensitive varieties which can tolerate the stresses of drought in high fields or deep standing water in low fields and other agronomic problems. In combination with the difficult hydrological regime restricting the production of rice crops to one a year, poor acidic and rather infertile soils generally low in phosphate, a shortage of draft and labour power availability for land preparation, a low proportion of rice lands under efficient irrigation (no more than 15%), low use of chemical and organic fertilizers, with the exception of irrigated dry season rice, and insecurity due to mines and onging unrest keep yields low.4 Most provinces experience food shortages from two to seven months of the year. In 1990 Cambodia had the first year of rice surplus in more than a decade, since then however, production has fallen behind subsistence levels and rice imports have been required. UNDP claim this is due to insecurity, repatriation,5 drought and flooding6 that damaged rice crops. In 1995, the World Food Programme estimated a food deficit of 90,000 tonnes. Dennis and Woodsworth (1992) suggest that food security is unlikely to be achieved while security concerns continue. However, an agricultural specialist with CIDSE, Harry Nesbit, expects 1996 to be a better year with food surpluses in several provinces (Phnom Penh Post, December 1995).