water in their own fields, causing water losses in conveyance and preventi ng downstream farmers from getting water. The rehabilitation of the existi ng irri-gation systems is extremely urgent to improve water use efficiency without much investments.

4.2 Improving on-farm water management for agricultural production.

4.2.1 Irrigated agriculture:Within each perfected irrigation system, further improvement of water use efficiency for crop watering can be obtained by each individual farmer. -securing field levees to prevent water leakage and seepage to oher fiels: -irrigating just sufficient water when the crop needs, instead of letting water running freely all time; -alternate irrigatin: precised volume of water is irrigated to the field at optimum intervals. -drip irrigation: widely used in dry and sandy areas, i.e. Israel. The precised amount of water is dripped onto the root zone of each plant without any wastage.

4.2.2 Non-irrigated agriculture; large arable areas in the world could not be economically served with irrigation system because water sources are ei- ther to far away or too deep. If their fainfall is more than 1,000 mm annually, some rain water harvesting technique may be applied to grow some crops. -Rainwater harvesting techniques: Normally in tropical region, the huge quantity of monsonn rains returns to eht sea after making flash floods and eroding hill tops and hill sides. Several techniques of rain water harvesting were developed:

i) Rainfed fanners now can excavate on-farm water reservoirs to trap rai n wa-ter or fresh flood water for use partially in the following dry seaso n.

ii) Recently the technique of dry seeded rice (DSR) has been developed an d is being practiced widely in rainfed areas of southern Vietnam. This tec h-nique makes use of every drop of rain water to successfully produce an e x-tra, short-duration rice crop before the main rice crop is transplanted.

iii) Small dams on the hilly catchments could store sufficient water for i rrigat-ing downstream crops, such the practice of terracing.

iv) Iow-Iift pumps --traditional or modern-- can bring water in creeks to irri-gate the crops nearby.