Crop Diversification in the Asia-Pacific region - United Nations in ...

3. PATTERNS OF CROP DIVERSIFICATION3.1 Crop Diversification in Rice LandRice is cultivated mainly in the Red River and Mekong River deltas. It is difficult topractice crop diversification in the rainy season in both river basins. From November to Mayor June, upland crop(s) can be grown in rotation with rice if farmers have the capacity toinvest on inputs and can get net returns from such cropping patterns. Upland crops inrotation with 2 rice crops are considered as “sub-crop(s)”, for which farmers need not paytaxes.In the Red River Delta, farmers have experience in growing an upland crop betweentwo rice crops. Spring rice is harvested in June and early ‘Mua’ rice crop is harvested at thebeginning of November. The possible upland crops to follow in this cropping pattern arepotato, vegetables, beans etc., or at the end of October it could be corn, sweet potato orsoybean. They are sown immediately after harvesting rice to avoid low temperature inwinter. Short duration and non-photosensitive rice varieties are chosen for the early Muarice crop. When necessary, crop seedlings for each hill are prepared by sowing seed inseparate boxed seedbeds made of leaves or plastic. Sometimes farmers put seedlings of theupland crop in rice fields about 10 days before harvesting the rice crop. Such croppingsystems (rice-rice-upland crop) are practiced on hundreds of thousands of hectares in theNorth, including the Red River Delta. Farmers can get more cash from the upland crops,especially by growing temperate vegetables such as cabbage, cauliflower and potato whichcan yield 15-20 tonnes/hectare. There is a residual effect from the upland crop for thesubsequent spring rice crop which includes minimizing land preparation and weed controlcosts, and spending less on fertilizer.In the Mekong delta, there is no problem of low temperatures. Farmers have grownmany upland crops in rotation with rice, except crops of temperate origin such ascauliflower. Farmers grow winter-spring rice from November to February, then follow upwith an upland crop before summer-autumn rice. It is interesting to note that in Longxuyenquadrangle, peanut has been grown on heavy soils (60 percent clay) on thousands ofhectares, which can yield 3-4 tonnes/hectare. The soils in this region are perhaps high inorganic matter (5-6 percent) and the difference of diurnal day/night temperature is high (6-10 o C). In terms of residues for the next rice crop, groundnut and vegetable soybean (65days) are considered the best. Generally, no tillage is applied for upland crops. Afterburning rice straw, farmers make planting holes and place the seed. One of the problems ofcrop intensification for crop diversification on rice land is damage from floods in the rainyseason. Floods occur from the middle of August and recede in November. Farmers areattempting to experiment with new technologies to overcome such constraints, for example,by using rice varieties with a duration below 90 days, or to apply a method of water seedingfor the winter-spring rice crop in order to shorten the duration of the crop in the field.In the 1960’s and 1970’s, Azolla was cultivated on a large scale in about 0.5 millionhectares in the north, especially in the Red River Delta. Azolla could replace 30-50 percentof N fertilizer for winter-spring or spring rice crop, but this practice has since beenabandoned. The reason is that Azolla cultivation requires a lot of labour with very preciseconditions in the winter season and farmers had to spray insecticides and apply phosphorousfertilizer every 5 days. They also had to manage water and remove dew to dry Azolla everyday when temperature was low (below 15 o C), if not, Azolla would die. Leguminous crops149