**2. Rice farming systems in Sri Lanka**

Rice is cultivated island-wide except at elevations 2000 m above sea level, and 75% of the rice lands in Sri Lanka are located in inland valley systems. The remaining 25% are in the terraced slopes of uplands, coastal plains, associated floodplains, and alluvial plains [30]. Rice cultivation is practiced following the "northeast" and "southwest" monsoons. The northeast monsoon is from December to February in the following

year, and the southwest is from May to August. The spatial distribution of rainfall brought by the monsoons defines two distinct climatic zones namely the "wet" and "dry" zones. The wet zone is in the southwestern sector of the island, whereas the dry zone is in the north, northeastern, and eastern parts of the country. The marginal areas between the two major zones are in the intermediate zone (**Figure 1**). The wet zone receives rain from the southwest monsoon and the amount varies from about 100 mm to over 3000 mm. In addition, from March to April wet zone receives the "first inter-monsoon" rain due to convectional influence, which can be over 250 mm to >700 mm. The dry zone receives rain from the northeast monsoon and the peak rainy season is from December to February, where the rainfall can be up to 177 mm to 1281 mm. The influence of depression and cyclone weather systems in the Bay of Bengal cause a "second inter-monsoon" starting from late September [33] or October to November [33–35]. The entire island receives in excess of 400 mm of rain from the second inter-monsoon. The two inter-monsoon periods contribute 37% of the total annual rainfall [36] and are critically important for the local crop calendars.

The special variability in rainfall along with soil, elevation, and hydrological regimes identify diverse rice farming environments in the country. However,

#### **Figure 1.**

*Land extends of the different farming systems: Major irrigated, minor irrigated, and rain-fed based on data from 2011 to 2021. Lands affected due to coastal and inland salinity and the border lines of wet, dry, and intermediate zones are indicated (data obtained from [31, 32]).*

### *The Scale and Complexity of Salinity Impacts on Sri Lankan Rice Farming Systems:… DOI: http://dx.doi.org/10.5772/intechopen.112651*

hydrological regimes are the principal determinant of rice production in the country, and three major rice farming systems are identified based on the source, supply, and use of surface water. These include rice lands under major and medium irrigation schemes, minor irrigation schemes, and rain-fed systems (**Figure 1**). Major irrigation systems are those that have a command area of >1000 ha, whereas the command area of medium schemes is between <80 ha and 1000 ha. Small tanks or minor irrigation systems are those having an irrigated command area of 80 ha or less [37]. The different rice production systems are geographically distributed (**Figure 1**). Rice land irrigated by major and medium irrigation schemes extends in the dry zone in an area of 730,000 ha in the north-central and the eastern parts of the island [38], where the water supply is from major tanks, rivers, and major stream diversion systems. Rice farming in major irrigation systems contributes 53% of the total annual rice production. Rice farming systems in the central dry and intermediate zones mostly depend on minor irrigation. Minor irrigation schemes operate under village tanks that are natural or man-made water reservoirs. Out of the total extent of the irrigated lands, 37% is in this category, and the minor irrigated systems contribute 20% to the total annual rice production in the country [39]. In the southwest, southern coastal region of the wet zone, and in the Jaffna peninsula, rice is cultivated under rain-fed systems. Of the total area of rice lands, 34.7% is rain-fed [31], and rain-fed systems contribute only 27% to the total rice production. All three systems, therefore, are critical in providing food supply and livelihoods for the local community.

Rice cultivation in irrigated and rain-fed systems is practiced in two major cropping seasons namely "major cultivation season" and "minor cultivation season," coinciding with the two monsoons (**Figure 2**). The "major cultivation season", which is from September to February coincides with the second inter-monsoon rain followed by the northeast monsoon. In the major season, cultivation starts in late September [33] with the onset of the second inter-monsoon, and the crop is harvested at the end of February. In the minor cultivation season cultivation starts during the end of March to mid-April with the first inter-monsoon rain, and the crop is harvested at the end of August [33]. In the major cultivation season with sufficient rainfall, rice is cultivated throughout the country. However, during the minor cultivation season, 21% of the rice lands are abandoned or used for the cultivation of other field crops due to water scarcity [31]. Rice lands under major irrigated farming systems are cultivated in two seasons, *viz*. major cultivation season and minor cultivation season per year. However, in minor irrigation systems, rice is cultivated in one season, the major cultivation season, with a few exceptions where irrigation is sufficient to cultivate two seasons. Wet zone rain-fed systems in the southwest are cultivated in two seasons depending on water availability, but rainfed systems in Jaffna peninsula are cultivated only during the major cultivation season [31].

Average annual rice production from major cultivation season, major irrigation schemes during the period 2011 to 2022, was 1,592,588 MT accounting for 54% of the total annual rice production. In the minor irrigation and rain-fed rice farming systems, the average rice production from major season over the same period was 702, 953 MT (31%) and 653, 288 MT (29%), respectively [31]. Rice production was significantly reduced in the minor cultivation season due to the limitation of water in the minor irrigation and rain-fed systems whereby the average production from the minor season during the period from 2011 to 2022 was 340,634 MT and 136,014 MT, respectively [40]. Therefore, 72% of the total production from the minor cultivation season is from rice under major irrigation schemes, and the average annual production over the period from 2011 to 2022 was 1,222,106 MT [31]. Accordingly, altogether,

#### **Figure 2.**

*Rainfall patterns and cultivation seasons in rice farming systems in Sri Lanka (adapted from [33–35]).*

#### **Figure 3.**

*Percentage of rice production in different districts in the two cropping seasons. Bar graphs indicate total seasonal rice production from the district as a percentage of the total national production from each season based on data from 2011 to 2021 (data obtained from [31]).*

>70% of the national annual rice production is from major irrigated systems (**Figure 3**). Therefore, major season cultivation in the major irrigated fields is the most productive rice farming environment or the "mega-rice cultivation system" in the country. Although the national contributions are less from rain-fed and minor irrigated systems where smallholder farmers cultivate rice on a semi-subsistence scale, those systems are critically important for national food security.

*The Scale and Complexity of Salinity Impacts on Sri Lankan Rice Farming Systems:… DOI: http://dx.doi.org/10.5772/intechopen.112651*
