Water availability, management practices and grain yield for deepwater rice in Northwest Cambodia

To characterize the annual and spatial variation in grain yield of deepwater rice on the floodplains of Tonle Sap Lake, Cambodia, from 2008 to 2011 we collected information on water availability, farming practices, and rice yield through intensive field monitoring, farmer interviews and yield sampling along a transect line of a water depth gradient. A total of 86 fields covering 91.5 ha were divided into 3 zones: an upper zone where only lowland rice (LR) was grown (referred to as ULR), a middle zone where both LR and floating rice (FR) were grown (MLR and MFR, respectively), and a lower zone closest to the lake where only FR was grown (LFR). The inundation from Tonle Sap Lake was within the normal range in 2008 and 2009, but it was extremely large and caused a complete crop failure in the study area in 2011. Conversely, no inundation occurred in 2010. Continuous standing of water started earlier (i.e., early September) in the lower zone and reached maximum depth in mid-October; water receded earlier (i.e., mid- to late November) in the upper zone than in the lower zone. FR was broadcast earlier (April) and harvested later (January) than LR (May and late November to December, respectively). A total of 6 LR varieties and 4 FR varieties with different heading times were planted during the study period. Maximum and average yields of LR were higher than those of FR, and from 2008 to 2011 the proportion of the LR variety Raing Chey planted steadily increased, whereas that of the late-maturing floating rice variety Veal Veng decreased. Grain yield in the middle zone was the lowest of the three zones. Maintenance of standing water after heading, larger input of N fertilizer, and appropriate weed management were found to contribute to higher yields for both LR and FR. These results should help farmers to cope with unpredictable flooding in areas where deepwater rice is cultivated.

► The inundation in the floodplain of Tonle Sap Lake showed large annual variations.
► Both lowland and floating rice were planted in the middle zone where yield was lowest.
► Lowland rice had larger maximum yield and its adoption increased.
► Maintenance of standing water after heading, larger input of N fertilizer, appropriate weed management contributed to higher yield.