Paddy in saline water: Analysing variety-specific effects of saline water intrusion on the technical efficiency of rice production in Vietnam

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Abstract
The purpose of our study is to evaluate the impact of saltwater intrusion on the productivity and technical efficiency (TE) of rice farms in Central Vietnam using the stochastic frontier (SF) production function. In contrast to existing studies, this research quantitatively analyses rice variety and season-differentiated impact of soil salinity (as measured by electrical conductivity (EC)) on the TE of rice production. The empirical results indicate that salinity induces significantly varying negative impacts on yield and technical inefficiency of rice farms depending on the salinity class, variety planted and the season. TE begins to sharply decline after reaching salinity class 3 (EC = 4–8 dS/m) and drops to zero under salinity class 4 (EC = 8–16 dS/m) unless salt-tolerant (ST) varieties are planted. A 1% increase in the EC level decreases rice yields by 0.24% in various SF models, while TE shows a cubic relationship with EC, with negative coefficients for linear and quadratic terms. A combination of farm plots consolidation, irrigation, integrated pest management, input optimisation and shifts in varietal selection can potentially offset the yield decline caused by saline intrusion for salinity classes 1 to 4, while adoption of ST varieties seems to be the best option for higher salinity classes over 4. These adaptation measures could also help farmers to avoid maladaptive options such as increased use of pesticide sprays to offset the yield losses due to soil salinity resulting from saline water intrusion. The insights offered by the study is applicable to coastal delta regions cultivating rice in whole of Asia and in other continents.

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