The semi-coastal areas of the Vietnamese Mekong Delta are suited to the rice/shrimp farming system which utilizes the wet season to cultivate rice and the dry season to produce shrimp when fresh water is scarce and the canal systems carry saline water (Leigh et al. 2017). The production system has high inherent risk with both rice and shrimp enterprises failing due to occasional extreme climatic events (Stewart-Koster et al. 2017). Farmers seeking to increase profitability and resilience to losses aim to decrease costs of production. Fertiliser costs are a significant percentage of the cost of rice production whilst shrimp production produces biological waste sludge which settles at the bottom of ditches surrounding and within the rice field. A controlled environment experiment was conducted to determine the nitrogen (N) mineralisation potential of this sludge. The N fertiliser value of this sludge was then evaluated in the field over two seasons on rice/shrimp farms at two locations in Vietnam.