Farmer's practices in sweetpotato production in the rice-based cropping system in the Mekong Delta, Vietnam

Sweetpotato is considered a climate adaptation option due to its relative tolerance to heat and salinity. The Mekong Region is the largest sweetpotato producing area in Vietnam with a stable export market demand. CGIAR Asian Mega Deltas Initiative has been exploring the potential of incorporating sweetpotato production in the rice cropping system in this region. A rice-sweetpotato crop rotation has a number of environmental and agronomic advantages for farmers such as pathogen control in the soil, greenhouse gas emission reduction, and the utilization of plots with increasing salinity in the areas where it will be difficult to grow rice in the future. Currently, rice-sweetpotato crop rotation is only implemented in some parts of Vinh Long province where sweetpotato is an important cash crop. Understanding farmers’ agronomic practices is the first step toward developing site-specific strategies and innovations. Therefore, in November 2023, a household survey was conducted of 89 sweetpotato growing households (11 female and 78 male farm managers) in Bình Tân district, Vĩnh Long province, Vietnam. The findings show that sweetpotato production areas per household vary from 0.3 to 8 ha with an average of 1.1 ha. All respondents purchase planting materials from seed producers or other farmers, with Japanese purple (Khoai lang tím Nhật) grown by 84% of the respondents. Sweetpotatoes can be planted year-round, but the majority (39%) starts planting in February, after the Lunar New Year. Maturity is 120-180 days with an average of around 150 days for both varieties. The average yield is 50t/ha for local white (Khoai Sua) and 32.8t/ha for Japanese purple (Khoai lang tím Nhật). 96% of harvested roots are sold to both domestic and global markets. The main rotation crop is rice (80%) followed by watermelon. Planting density is very high with around 180,000 cuttings per ha (162 cuttings per 9 square meters), which is a farmer strategy to meet the market demand for small-sized roots (300-400g). 92% of farmers use N, P2O5, and K2O fertilizers at an average 15.6kg, 15kg and 11kg/ha respectively. However, the total quantity of NPK fertilizer application (including supplemental ingredients) is very high, averaging more than 900kg/ha. Pests and pathogens are a major cause of crop loss. The most affected disease is foot rot (Diaporthe destruens) which 73% of respondents reported. The maximum damage it causes is estimated as 24.8% (5-90%). The most common pest is sweetpotato weevil, reported by 57% of respondents. The estimated maximum damage from the weevil is 28% (1-45%). Most farmers apply synthetic fungicides and insecticides for both prevention and counter actions, typically spraying 10 times or more in one growing season, at an average of 68 liters per ha. The findings from this household survey will be used for on-going sweetpotato breeding experiments in the Mekong Region. Identified constraints will be addressed in collaboration with partners.