The impact of salinity on paddy production and possible varietal portfolio transition: a Vietnamese case study

Increasing soil salinisation is an environmental stressor that causes significant reduction in crop productivity and increases the risk of farming and hence reduces the cultivated land area. For these reasons, soil salinisation is considered to be one of the most serious problems threatening food security. In the north central coastal region of Vietnam, saltwater intrusion in the dry season is a major concern for rice farming. To better understand the adverse impacts of soil salinisation in crops, this study investigates impacts of salinity on mean and variability of rice yields in four communes of Thua Thien Hue Province. In addition, the study looks at possible changes in the portfolio of rice cultivars, which would offer farmers the potential to increase yields and decrease yield variability simultaneously. Results clearly showed that salinity had an impact on yield levels, resulting in an average yield loss of 0.164 tonnes/ha from mean yield levels per unit increase of electrical conductivity. The results did not show that increasing salinity contributes to an increase in variability of yields, but points to the fact that saline water intrusion may lead to consistently lower yields in the study area. Results also indicate that farmers with smaller, scattered plots could be disproportionately affected by salinity and be less capable of managing the saline soils. In addition, saline conditions may also drive the increased use of environmentally damaging inputs, such as pesticides, to offset the decline in yields and thereby potentially lead to a vicious circle. Utilisation of an optimised portfolio of rice varieties that combine profit maximisation and risk reduction reveals that farmers can benefit from revised portfolios of existing varieties at initial salinity levels, but need to include salt-resistant varieties in the portfolio as salinity levels increase.