Socio-economic evaluation on how crop rotations on clayey soils affect rice yield and farmers' income in the Mekong Delta, Vietnam

Declining land productivity is a major problem faced by small holder farmers in the Mekong Delta today. Low soil quality is one of the greatest long-term challenges for farmers in rice monocultures on alluvial soil. In order to better understand how farm characteristics and crop rotations affect crop yield and income, a socio-economic evaluation among smallholder farmers were conducted in Cai Lay District, Tien Giang province. During farm household surveys, information on household characteristics, farm cropping activities, farm production practices and performance, and household income was collected. Four types of farming practices were observed, one based on traditional rice monoculture with three rice crops per year (RRR), one based on a crop rotation with two rice and one upland crop (RUR), one based on a crop rotation with one rice and two upland crops (RUU), and a fourth based on upland crop monocultures (UUU). From the results of interviews with the farmers, it was found that rotations with RUR or RUU gave higher rice yields than RRR. The rice yield in the last five years increased when rotations with upland crops were implemented (RUR and RUU), which was strongly in contrast with the rice yield decrease over the last five years for rice monoculture systems (RRR). The benefit-to-cost ratio was the highest for RUR. Interestingly, in RUR and RUU, farmers apply less fertilizer and pesticide for rice production compared to RRR. The survey revealed that many farmers had a tendency to apply too much nitrogen as a way to compensate for the reduced rice growth due to land degradation in RRR. Regarding farm size in the study area, the average size is about 0.62 ha. The size of small farms is 0.36 ha and such small farms are found in UUU systems. The largest farms (0.91 ha) were found in RRR systems. Farms of 0.68 ha and 0.43 ha are found in RUR and RUU systems, respectively. The average profit of RUR and RUU was 2,490 USD/ha/year and 2,686 USD/ha/year, respectively. Those were higher than the profit of RRR farming (1,094 USD/ha/year), but lower than the profit from UUU systems (3,058 USD/ha/year)